# Publications

### 2018

 (J) Janet van den Boer, Annemiek van der Lee, Lingchuan Zhou, Vasileios Papapanagiotou, Christos Diou, Anastasios Delopoulos and Monica Mars The SPLENDID Eating Detection Sensor: Development and Feasibility Study, 6, (9), pp. 170, 2018 Sep [Abstract][BibTex]The available methods for monitoring food intake---which for a great part rely on self-report---often provide biased and incomplete data. Currently, no good technological solutions are available. Hence, the SPLENDID eating detection sensor (an ear-worn device with an air microphone and a photoplethysmogram [PPG] sensor) was developed to enable complete and objective measurements of eating events. The technical performance of this device has been described before. To date, literature is lacking a description of how such a device is perceived and experienced by potential users. Objective: The objective of our study was to explore how potential users perceive and experience the SPLENDID eating detection sensor. Methods: Potential users evaluated the eating detection sensor at different stages of its development: (1) At the start, 12 health professionals (eg, dieticians, personal trainers) were interviewed and a focus group was held with 5 potential end users to find out their thoughts on the concept of the eating detection sensor. (2) Then, preliminary prototypes of the eating detection sensor were tested in a laboratory setting where 23 young adults reported their experiences. (3) Next, the first wearable version of the eating detection sensor was tested in a semicontrolled study where 22 young, overweight adults used the sensor on 2 separate days (from lunch till dinner) and reported their experiences. (4) The final version of the sensor was tested in a 4-week feasibility study by 20 young, overweight adults who reported their experiences. Results: Throughout all the development stages, most individuals were enthusiastic about the eating detection sensor. However, it was stressed multiple times that it was critical that the device be discreet and comfortable to wear for a longer period. In the final study, the eating detection sensor received an average grade of 3.7 for wearer comfort on a scale of 1 to 10. Moreover, experienced discomfort was the main reason for wearing the eating detection sensor <2 hours a day. The participants reported having used the eating detection sensor on 19/28 instructed days on average. Conclusions: The SPLENDID eating detection sensor, which uses an air microphone and a PPG sensor, is a promising new device that can facilitate the collection of reliable food intake data, as shown by its technical potential. Potential users are enthusiastic, but to be successful wearer comfort and discreetness of the device need to be improved.@article{2018Boer,author={Janet van den Boer and Annemiek van der Lee and Lingchuan Zhou and Vasileios Papapanagiotou and Christos Diou and Anastasios Delopoulos and Monica Mars},title={The SPLENDID Eating Detection Sensor: Development and Feasibility Study},journal={The SPLENDID Eating Detection Sensor: Development and Feasibility Study},volume={6},number={9},pages={170},year={2018},month={09},date={2018-09-04},doi={https://doi.org/10.2196/mhealth.9781},issn={2291-5222},abstract={The available methods for monitoring food intake---which for a great part rely on self-report---often provide biased and incomplete data. Currently, no good technological solutions are available. Hence, the SPLENDID eating detection sensor (an ear-worn device with an air microphone and a photoplethysmogram [PPG] sensor) was developed to enable complete and objective measurements of eating events. The technical performance of this device has been described before. To date, literature is lacking a description of how such a device is perceived and experienced by potential users. Objective: The objective of our study was to explore how potential users perceive and experience the SPLENDID eating detection sensor. Methods: Potential users evaluated the eating detection sensor at different stages of its development: (1) At the start, 12 health professionals (eg, dieticians, personal trainers) were interviewed and a focus group was held with 5 potential end users to find out their thoughts on the concept of the eating detection sensor. (2) Then, preliminary prototypes of the eating detection sensor were tested in a laboratory setting where 23 young adults reported their experiences. (3) Next, the first wearable version of the eating detection sensor was tested in a semicontrolled study where 22 young, overweight adults used the sensor on 2 separate days (from lunch till dinner) and reported their experiences. (4) The final version of the sensor was tested in a 4-week feasibility study by 20 young, overweight adults who reported their experiences. Results: Throughout all the development stages, most individuals were enthusiastic about the eating detection sensor. However, it was stressed multiple times that it was critical that the device be discreet and comfortable to wear for a longer period. In the final study, the eating detection sensor received an average grade of 3.7 for wearer comfort on a scale of 1 to 10. Moreover, experienced discomfort was the main reason for wearing the eating detection sensor <2 hours a day. The participants reported having used the eating detection sensor on 19/28 instructed days on average. Conclusions: The SPLENDID eating detection sensor, which uses an air microphone and a PPG sensor, is a promising new device that can facilitate the collection of reliable food intake data, as shown by its technical potential. Potential users are enthusiastic, but to be successful wearer comfort and discreetness of the device need to be improved.}} (J) Christos Diou, Pantelis Lelekas and Anastasios Delopoulos Journal of Imaging, 4, (11), pp. 125, 2018 Oct [Abstract][BibTex]Background: Evidence-based policymaking requires data about the local population’s socioeconomic status (SES) at detailed geographical level, however, such information is often not available, or is too expensive to acquire. Researchers have proposed solutions to estimate SES indicators by analyzing Google Street View images, however, these methods are also resource-intensive, since they require large volumes of manually labeled training data. (2) Methods: We propose a methodology for automatically computing surrogate variables of SES indicators using street images of parked cars and deep multiple instance learning. Our approach does not require any manually created labels, apart from data already available by statistical authorities, while the entire pipeline for image acquisition, parked car detection, car classification, and surrogate variable computation is fully automated. The proposed surrogate variables are then used in linear regression models to estimate the target SES indicators. (3) Results: We implement and evaluate a model based on the proposed surrogate variable at 30 municipalities of varying SES in Greece. Our model has R2=0.76 and a correlation coefficient of 0.874 with the true unemployment rate, while it achieves a mean absolute percentage error of 0.089 and mean absolute error of 1.87 on a held-out test set. Similar results are also obtained for other socioeconomic indicators, related to education level and occupational prestige. (4) Conclusions: The proposed methodology can be used to estimate SES indicators at the local level automatically, using images of parked cars detected via Google Street View, without the need for any manual labeling effort@article{Diou2018JI,author={Christos Diou and Pantelis Lelekas and Anastasios Delopoulos},title={Image-Based Surrogates of Socio-Economic Status in Urban Neighborhoods Using Deep Multiple Instance Learning},journal={Journal of Imaging},volume={4},number={11},pages={125},year={2018},month={10},date={2018-10-23},doi={http://10.3390/jimaging4110125},issn={2313-433X},abstract={Background: Evidence-based policymaking requires data about the local population’s socioeconomic status (SES) at detailed geographical level, however, such information is often not available, or is too expensive to acquire. Researchers have proposed solutions to estimate SES indicators by analyzing Google Street View images, however, these methods are also resource-intensive, since they require large volumes of manually labeled training data. (2) Methods: We propose a methodology for automatically computing surrogate variables of SES indicators using street images of parked cars and deep multiple instance learning. Our approach does not require any manually created labels, apart from data already available by statistical authorities, while the entire pipeline for image acquisition, parked car detection, car classification, and surrogate variable computation is fully automated. The proposed surrogate variables are then used in linear regression models to estimate the target SES indicators. (3) Results: We implement and evaluate a model based on the proposed surrogate variable at 30 municipalities of varying SES in Greece. Our model has R2=0.76 and a correlation coefficient of 0.874 with the true unemployment rate, while it achieves a mean absolute percentage error of 0.089 and mean absolute error of 1.87 on a held-out test set. Similar results are also obtained for other socioeconomic indicators, related to education level and occupational prestige. (4) Conclusions: The proposed methodology can be used to estimate SES indicators at the local level automatically, using images of parked cars detected via Google Street View, without the need for any manual labeling effort}} (J) Maryam Esfandiari, Vasilis Papapanagiotou, Christos Diou, Modjtaba Zandian, Jenny Nolstam, Per Södersten and Cecilia Bergh JoVE, (135), 2018 May [Abstract][BibTex]Subjects eat food from a plate that sits on a scale connected to a computer that records the weight loss of the plate during the meal and makes up a curve of food intake, meal duration and rate of eating modeled by a quadratic equation. The purpose of the method is to change eating behavior by providing visual feedback on the computer screen that the subject can adapt to because her/his own rate of eating appears on the screen during the meal. The data generated by the method is automatically analyzed and fitted to the quadratic equation using a custom made algorithm. The method has the advantage of recording eating behavior objectively and offers the possibility of changing eating behavior both in experiments and in clinical practice. A limitation may be that experimental subjects are affected by the method. The same limitation may be an advantage in clinical practice, as eating behavior is more easily stabilized by the method. A treatment that uses this method has normalized body weight and restored the health of several hundred patients with anorexia nervosa and other eating disorders and has reduced the weight and improved the health of severely overweight patients.@article{Esfandiari2018,author={Maryam Esfandiari and Vasilis Papapanagiotou and Christos Diou and Modjtaba Zandian and Jenny Nolstam and Per Södersten and Cecilia Bergh},title={Control of Eating Behavior Using a Novel Feedback System},journal={JoVE},number={135},year={2018},month={05},date={2018-05-08},doi={http://10.3791/57432},abstract={Subjects eat food from a plate that sits on a scale connected to a computer that records the weight loss of the plate during the meal and makes up a curve of food intake, meal duration and rate of eating modeled by a quadratic equation. The purpose of the method is to change eating behavior by providing visual feedback on the computer screen that the subject can adapt to because her/his own rate of eating appears on the screen during the meal. The data generated by the method is automatically analyzed and fitted to the quadratic equation using a custom made algorithm. The method has the advantage of recording eating behavior objectively and offers the possibility of changing eating behavior both in experiments and in clinical practice. A limitation may be that experimental subjects are affected by the method. The same limitation may be an advantage in clinical practice, as eating behavior is more easily stabilized by the method. A treatment that uses this method has normalized body weight and restored the health of several hundred patients with anorexia nervosa and other eating disorders and has reduced the weight and improved the health of severely overweight patients.}} (J) George Mamalakis, Christos Diou, Andreas Symeonidis and Leonidas Georgiadis Neural Computing and Applications, 2018 Jul [Abstract][BibTex]In this work, we propose a methodology for reducing false alarms in file system intrusion detection systems, by taking into account the daemon's file system footprint. More specifically, we experimentally show that sequences of outliers can serve as a distinguishing characteristic between true and false positives, and we show how analysing sequences of outliers can lead to lower false positive rates, while maintaining high detection rates. Based on this analysis, we developed an anomaly detection filter that learns outlier sequences using k-nearest neighbours with normalised longest common subsequence. Outlier sequences are then used as a filter to reduce false positives on the {\$}{\$}FI^2DS{\$}{\$}FI2DSfile system intrusion detection system. This filter is evaluated on both overlapping and non-overlapping sequences of outliers. In both cases, experiments performed on three real-world web servers and a honeynet show that our approach achieves significant false positive reduction rates (up to 50 times), without any degradation of the corresponding true positive detection rates.@article{Mamalakis2018,author={George Mamalakis and Christos Diou and Andreas Symeonidis and Leonidas Georgiadis},title={Of daemons and men: reducing false positive rate in intrusion detection systems with file system footprint analysis},journal={Neural Computing and Applications},year={2018},month={07},date={2018-07-05},doi={http://10.1007/s00521-018-3550-x},issn={1433-3058},abstract={In this work, we propose a methodology for reducing false alarms in file system intrusion detection systems, by taking into account the daemon\'s file system footprint. More specifically, we experimentally show that sequences of outliers can serve as a distinguishing characteristic between true and false positives, and we show how analysing sequences of outliers can lead to lower false positive rates, while maintaining high detection rates. Based on this analysis, we developed an anomaly detection filter that learns outlier sequences using k-nearest neighbours with normalised longest common subsequence. Outlier sequences are then used as a filter to reduce false positives on the {\\$}{\\$}FI^2DS{\\$}{\\$}FI2DSfile system intrusion detection system. This filter is evaluated on both overlapping and non-overlapping sequences of outliers. In both cases, experiments performed on three real-world web servers and a honeynet show that our approach achieves significant false positive reduction rates (up to 50 times), without any degradation of the corresponding true positive detection rates.}} (J) Ioannis Sarafis, Christos Diou and Anastasios Delopoulos CoRR, abs/1809.06124, 2018 Sep [Abstract][BibTex][pdf]Weighted SVM (or fuzzy SVM) is the most widely used SVM variant owning its effectiveness to the use of instance weights. Proper selection of the instance weights can lead to increased generalization performance. In this work, we extend the span error bound theory to weighted SVM and we introduce effective hyperparameter selection methods for the weighted SVM algorithm. The significance of the presented work is that enables the application of span bound and span-rule with weighted SVM. The span bound is an upper bound of the leave-one-out error that can be calculated using a single trained SVM model. This is important since leave-one-out error is an almost unbiased estimator of the test error. Similarly, the span-rule gives the actual value of the leave-one-out error. Thus, one can apply span bound and span-rule as computationally lightweight alternatives of leave-one-out procedure for hyperparameter selection. The main theoretical contributions are: (a) we prove the necessary and sufficient condition for the existence of the span of a support vector in weighted SVM; and (b) we prove the extension of span bound and span-rule to weighted SVM. We experimentally evaluate the span bound and the span-rule for hyperparameter selection and we compare them with other methods that are applicable to weighted SVM: the K-fold cross-validation and the $\xi - \alpha$ bound. Experiments on 14 benchmark data sets and data sets with importance scores for the training instances show that: (a) the condition for the existence of span in weighted SVM is satisfied almost always; (b) the span-rule is the most effective method for weighted SVM hyperparameter selection; (c) the span-rule is the best predictor of the test error in the mean square error sense; and (d) the span-rule is efficient and, for certain problems, it can be calculated faster than K-fold cross-validation.@article{Sarafis2018CoRR,author={Ioannis Sarafis and Christos Diou and Anastasios Delopoulos},title={Span error bound for weighted SVM with applications in hyperparameter selection (preprint)},journal={CoRR},volume={abs/1809.06124},year={2018},month={09},date={2018-09-17},url={https://arxiv.org/pdf/1809.06124.pdf},abstract={Weighted SVM (or fuzzy SVM) is the most widely used SVM variant owning its effectiveness to the use of instance weights. Proper selection of the instance weights can lead to increased generalization performance. In this work, we extend the span error bound theory to weighted SVM and we introduce effective hyperparameter selection methods for the weighted SVM algorithm. The significance of the presented work is that enables the application of span bound and span-rule with weighted SVM. The span bound is an upper bound of the leave-one-out error that can be calculated using a single trained SVM model. This is important since leave-one-out error is an almost unbiased estimator of the test error. Similarly, the span-rule gives the actual value of the leave-one-out error. Thus, one can apply span bound and span-rule as computationally lightweight alternatives of leave-one-out procedure for hyperparameter selection. The main theoretical contributions are: (a) we prove the necessary and sufficient condition for the existence of the span of a support vector in weighted SVM; and (b) we prove the extension of span bound and span-rule to weighted SVM. We experimentally evaluate the span bound and the span-rule for hyperparameter selection and we compare them with other methods that are applicable to weighted SVM: the K-fold cross-validation and the $\\xi - \\alpha$ bound. Experiments on 14 benchmark data sets and data sets with importance scores for the training instances show that: (a) the condition for the existence of span in weighted SVM is satisfied almost always; (b) the span-rule is the most effective method for weighted SVM hyperparameter selection; (c) the span-rule is the best predictor of the test error in the mean square error sense; and (d) the span-rule is efficient and, for certain problems, it can be calculated faster than K-fold cross-validation.}} (J) Vasilis Papapanagiotou, Christos Diou, Ioannis Ioakimidis, Per Sodersten and Anastasios Delopoulos IEEE Journal of Biomedical and Health Informatics, PP, (99), pp. 1-1, 2018 Mar [Abstract][BibTex][pdf]The structure of the cumulative food intake (CFI) curve has been associated with obesity and eating disorders. Scales that record the weight loss of a plate from which a subject eats food are used for capturing this curve; however, their measurements are contaminated by additive noise and are distorted by certain types of artifacts. This paper presents an algorithm for automatically processing continuous in-meal weight measurements in order to extract the clean CFI curve and in-meal eating indicators, such as total food intake and food intake rate. The algorithm relies on the representation of the weight-time series by a string of symbols that correspond to events such as bites or food additions. A context-free grammar is next used to model a meal as a sequence of such events. The selection of the most likely parse tree is finally used to determine the predicted eating sequence. The algorithm is evaluated on a dataset of 113 meals collected using the Mandometer, a scale that continuously samples plate weight during eating. We evaluate the effectiveness for seven indicators, and for bite-instance detection. We compare our approach with three state-of-the-art algorithms, and achieve the lowest error rates for most indicators (24 g for total meal weight). The proposed algorithm extracts the parameters of the CFI curve automatically, eliminating the need for manual data processing, and thus facilitating large-scale studies of eating behavior.@article{Vassilis2018,author={Vasilis Papapanagiotou and Christos Diou and Ioannis Ioakimidis and Per Sodersten and Anastasios Delopoulos},title={Automatic analysis of food intake and meal microstructure based on continuous weight measurements},journal={IEEE Journal of Biomedical and Health Informatics},volume={PP},number={99},pages={1-1},year={2018},month={03},date={2018-03-05},url={http://mug.ee.auth.gr/wp-content/uploads/papapanagiotou2018automated.pdf},doi={http://10.1109/JBHI.2018.2812243},abstract={The structure of the cumulative food intake (CFI) curve has been associated with obesity and eating disorders. Scales that record the weight loss of a plate from which a subject eats food are used for capturing this curve; however, their measurements are contaminated by additive noise and are distorted by certain types of artifacts. This paper presents an algorithm for automatically processing continuous in-meal weight measurements in order to extract the clean CFI curve and in-meal eating indicators, such as total food intake and food intake rate. The algorithm relies on the representation of the weight-time series by a string of symbols that correspond to events such as bites or food additions. A context-free grammar is next used to model a meal as a sequence of such events. The selection of the most likely parse tree is finally used to determine the predicted eating sequence. The algorithm is evaluated on a dataset of 113 meals collected using the Mandometer, a scale that continuously samples plate weight during eating. We evaluate the effectiveness for seven indicators, and for bite-instance detection. We compare our approach with three state-of-the-art algorithms, and achieve the lowest error rates for most indicators (24 g for total meal weight). The proposed algorithm extracts the parameters of the CFI curve automatically, eliminating the need for manual data processing, and thus facilitating large-scale studies of eating behavior.}}

### 2018

 (M) Christos Diou, Ioannis Ioakeimidis, Evangelia Charmandari, Penio Kassaric, Irini Lekka, Monica Mars, Cecilia Bergh, Tahar Kechadi, Gerardine Doyle, Grace O’Malley, Rachel Heimeier, Anna Karin Lindroos, Sofoklis Sotiriou, Evangelia Koukoula, Sergio Guillén, George Lymperopoulos, Nicos Maglaveras and Anastasios Delopoulos Athens, Greece, 2018 Sep [Abstract][BibTex]Background: Childhood obesity is a major global and European public health problem. The need for community-targeted actions has long been recognized, however it has been prevented by the lack of monitoring and evaluation framework, and the methodological inability to objectively quantify the local community characteristics in a reasonable timeframe. Recent technological achievements in mobile and wearable electronics and Big Data infrastructures allow the engagement of European citizens in the data collection process.@misc{Diou2018ESPE,author={Christos Diou and Ioannis Ioakeimidis and Evangelia Charmandari and Penio Kassaric and Irini Lekka and Monica Mars and Cecilia Bergh and Tahar Kechadi and Gerardine Doyle and Grace O’Malley and Rachel Heimeier and Anna Karin Lindroos and Sofoklis Sotiriou and Evangelia Koukoula and Sergio Guillén and George Lymperopoulos and Nicos Maglaveras and Anastasios Delopoulos},title={BigO: Big Data Against Childhood Obesity},howpublished={57th Annual ESPE},address={Athens, Greece},year={2018},month={09},date={2018-09-27},abstract={Background: Childhood obesity is a major global and European public health problem. The need for community-targeted actions has long been recognized, however it has been prevented by the lack of monitoring and evaluation framework, and the methodological inability to objectively quantify the local community characteristics in a reasonable timeframe. Recent technological achievements in mobile and wearable electronics and Big Data infrastructures allow the engagement of European citizens in the data collection process.}}

### 2017

 (J) Billy Langlet, Anna Anvret, Christos Maramis, Ioannis Moulos, Vasileios Papapanagiotou, Christos Diou, Eirini Lekka, Rachel Heimeier, Anastasios Delopoulos and Ioannis Ioakimidis Behaviour & Information Technology, 36, (10), pp. 1005-1013, 2017 May [Abstract][BibTex][pdf]Studying eating behaviours is important in the fields of eating disorders and obesity. However, the current methodologies of quantifying eating behaviour in a real-life setting are lacking, either in reliability (e.g. self-reports) or in scalability. In this descriptive study, we deployed previously evaluated laboratory-based methodologies in a Swedish high school, using the Mandometer®, together with video cameras and a dedicated mobile app in order to record eating behaviours in a sample of 41 students, 16–17 years old. Without disturbing the normal school life, we achieved a 97% data-retention rate, using methods fully accepted by the target population. The overall eating style of the students was similar across genders, with male students eating more than females, during lunches of similar lengths. While both groups took similar number of bites, males took larger bites across the meal. Interestingly, the recorded school lunches were as long as lunches recorded in a laboratory setting, which is characterised by the absence of social interactions and direct access to additional food. In conclusion, a larger scale use of our methods is feasible, but more hypotheses-based studies are needed to fully describe and evaluate the interactions between the school environment and the recorded eating behaviours.@article{Langlet2017,author={Billy Langlet and Anna Anvret and Christos Maramis and Ioannis Moulos and Vasileios Papapanagiotou and Christos Diou and Eirini Lekka and Rachel Heimeier and Anastasios Delopoulos and Ioannis Ioakimidis},title={Objective measures of eating behaviour in a Swedish high school},journal={Behaviour & Information Technology},volume={36},number={10},pages={1005-1013},year={2017},month={05},date={2017-05-06},url={https://doi.org/10.1080/0144929X.2017.1322146},doi={http://10.1080/0144929X.2017.1322146},abstract={Studying eating behaviours is important in the fields of eating disorders and obesity. However, the current methodologies of quantifying eating behaviour in a real-life setting are lacking, either in reliability (e.g. self-reports) or in scalability. In this descriptive study, we deployed previously evaluated laboratory-based methodologies in a Swedish high school, using the Mandometer®, together with video cameras and a dedicated mobile app in order to record eating behaviours in a sample of 41 students, 16–17 years old. Without disturbing the normal school life, we achieved a 97% data-retention rate, using methods fully accepted by the target population. The overall eating style of the students was similar across genders, with male students eating more than females, during lunches of similar lengths. While both groups took similar number of bites, males took larger bites across the meal. Interestingly, the recorded school lunches were as long as lunches recorded in a laboratory setting, which is characterised by the absence of social interactions and direct access to additional food. In conclusion, a larger scale use of our methods is feasible, but more hypotheses-based studies are needed to fully describe and evaluate the interactions between the school environment and the recorded eating behaviours.}}

### 2015

 (J) Ioannis Sarafis, Christos Diou and Anastasios Delopoulos "Building effective SVM concept detectors from clickthrough data for large-scale image retrieval" International Journal of Multimedia Information Retrieval, 4, (2), pp. 129-142, 2015 Jun [Abstract][BibTex][pdf]Clickthrough data is a source of information that can be used for automatically building concept detectors for image retrieval. Previous studies, however, have shown that in many cases the resulting training sets suffer from severe label noise that has a significant impact in the SVM concept detector performance. This paper evaluates and proposes a set of strategies for automatically building effective concept detectors from clickthrough data. These strategies focus on: (1) automatic training set generation; (2) assignment of label confidence weights to the training samples and (3) using these weights at the classifier level to improve concept detector effectiveness. For training set selection and in order to assign weights to individual training samples three Information Retrieval (IR) models are examined: vector space models, BM25 and language models. Three SVM variants that take into account importance at the classifier level are evaluated and compared to the standard SVM: the Fuzzy SVM, the Power SVM, and the Bilateral-weighted Fuzzy SVM. Experiments conducted on the MM Grand Challenge dataset (consisting of 1M images and 82.3M unique clicks) for 40 concepts demonstrate that (1) on average, all weighted SVM variants are more effective than the standard SVM; (2) the vector space model produces the best training sets and best weights; (3) the Bilateral-weighted Fuzzy SVM produces the best results but is very sensitive to weight assignment and (4) the Fuzzy SVM is the most robust training approach for varying levels of label noise.@article{Sarafis2015Building,author={Ioannis Sarafis and Christos Diou and Anastasios Delopoulos},title={Building effective SVM concept detectors from clickthrough data for large-scale image retrieval},journal={International Journal of Multimedia Information Retrieval},volume={4},number={2},pages={129-142},year={2015},month={06},date={2015-06-01},url={http://link.springer.com/article/10.1007/s13735-015-0080-5},doi={http://10.1007/s13735-015-0080-5},abstract={Clickthrough data is a source of information that can be used for automatically building concept detectors for image retrieval. Previous studies, however, have shown that in many cases the resulting training sets suffer from severe label noise that has a significant impact in the SVM concept detector performance. This paper evaluates and proposes a set of strategies for automatically building effective concept detectors from clickthrough data. These strategies focus on: (1) automatic training set generation; (2) assignment of label confidence weights to the training samples and (3) using these weights at the classifier level to improve concept detector effectiveness. For training set selection and in order to assign weights to individual training samples three Information Retrieval (IR) models are examined: vector space models, BM25 and language models. Three SVM variants that take into account importance at the classifier level are evaluated and compared to the standard SVM: the Fuzzy SVM, the Power SVM, and the Bilateral-weighted Fuzzy SVM. Experiments conducted on the MM Grand Challenge dataset (consisting of 1M images and 82.3M unique clicks) for 40 concepts demonstrate that (1) on average, all weighted SVM variants are more effective than the standard SVM; (2) the vector space model produces the best training sets and best weights; (3) the Bilateral-weighted Fuzzy SVM produces the best results but is very sensitive to weight assignment and (4) the Fuzzy SVM is the most robust training approach for varying levels of label noise.}}

### 2014

 (C) Christos Maramis, Christos Diou, Ioannis Ioakeimidis, Irini Lekka, Gabriela Dudnik, Monica Mars, Nikos Maglaveras, Cecilia Bergh and Anastasios Delopoulos "SPLENDID: Preventing Obesity and Eating Disorders through Long-term Behavioural Modifications" MOBIHEALTH 2014, ATHENES, Greece, 2014 Nov [Abstract][BibTex]@inproceedings{Maramis2017SPLENDID,author={Christos Maramis and Christos Diou and Ioannis Ioakeimidis and Irini Lekka and Gabriela Dudnik and Monica Mars and Nikos Maglaveras and Cecilia Bergh and Anastasios Delopoulos},title={SPLENDID: Preventing Obesity and Eating Disorders through Long-term Behavioural Modifications},booktitle={MOBIHEALTH 2014},address={ATHENES, Greece},year={2014},month={11},date={2014-11-01}} (C) Ioannis Sarafis, Christos Diou and Anastasios Delopoulos "Building Robust Concept Detectors from Clickthrough Data: A Study in the MSR-Bing Dataset" 2014 9th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP), pp. 66-71, 2014 Nov [Abstract][BibTex][pdf]In this paper we extend our previous work on strategies for automatically constructing noise resilient SVM detectors from click through data for large scale concept-based image retrieval. First, search log data is used in conjunction with Information Retrieval (IR) models to score images with respect to each concept. The IR models evaluated in this work include Vector Space Models (VSM), BM25 and Language Models (LM). The scored images are then used to create training sets for SVM and appropriate sample weights for two SVM variants: the Fuzzy SVM (FSVM) and the Power SVM (PSVM). These SVM variants incorporate weights for each individual training sample and can therefore be used to model label uncertainty at the classifier level. Experiments on the MSR-Bing Image Retrieval Grand Challenge dataset (consisting of 1M images and 82.3M unique clicks) show that FSVM is the most robust SVM algorithm for handling label noise and that the highest performance is achieved with weights derived from VSM. These results extend our previous findings on the value of FSVM from professional image archives to large-scale general purpose search engines, and furthermore identify VSM as the most appropriate sample weighting model.@inproceedings{Sarafis2014Building,author={Ioannis Sarafis and Christos Diou and Anastasios Delopoulos},title={Building Robust Concept Detectors from Clickthrough Data: A Study in the MSR-Bing Dataset},booktitle={2014 9th International Workshop on Semantic and Social Media Adaptation and Personalization (SMAP)},pages={66-71},year={2014},month={11},date={2014-11-01},url={http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6978955},doi={http://10.1109/SMAP.2014},abstract={In this paper we extend our previous work on strategies for automatically constructing noise resilient SVM detectors from click through data for large scale concept-based image retrieval. First, search log data is used in conjunction with Information Retrieval (IR) models to score images with respect to each concept. The IR models evaluated in this work include Vector Space Models (VSM), BM25 and Language Models (LM). The scored images are then used to create training sets for SVM and appropriate sample weights for two SVM variants: the Fuzzy SVM (FSVM) and the Power SVM (PSVM). These SVM variants incorporate weights for each individual training sample and can therefore be used to model label uncertainty at the classifier level. Experiments on the MSR-Bing Image Retrieval Grand Challenge dataset (consisting of 1M images and 82.3M unique clicks) show that FSVM is the most robust SVM algorithm for handling label noise and that the highest performance is achieved with weights derived from VSM. These results extend our previous findings on the value of FSVM from professional image archives to large-scale general purpose search engines, and furthermore identify VSM as the most appropriate sample weighting model.}} (C) Ioannis Sarafis, Christos Diou, Theodora Tsikrika and Anastasios Delopoulos "Weighted SVM from clickthrough data for image retrieval" 2014 IEEE International Conference on Image Processing (ICIP), pp. 3013-3017, 2014 Aug [Abstract][BibTex][pdf]In this paper we propose a novel approach to training noise-resilient concept detectors from clickthrough data collected by image search engines. We take advantage of the query logs to automatically produce concept detector training sets; these suffer though from label noise, i.e., erroneously assigned labels. We explore two alternative approaches for handling noisy training data at the classifier level by training concept detectors with two SVM variants: the Fuzzy SVM and the Power SVM. Experimental results on images collected from a professional image search engine indicate that 1) Fuzzy SVM outperforms both SVM and Power SVM and is the most effective approach towards handling label noise and 2) the performance gain of Fuzzy SVM compared to SVM increases progressively with the noise level in the training sets.@inproceedings{Sarafis2014Weighted,author={Ioannis Sarafis and Christos Diou and Theodora Tsikrika and Anastasios Delopoulos},title={Weighted SVM from clickthrough data for image retrieval},booktitle={2014 IEEE International Conference on Image Processing (ICIP)},pages={3013-3017},year={2014},month={08},date={2014-08-01},url={http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=7025609},doi={http://10.1109/ICIP.2014.7025609},abstract={In this paper we propose a novel approach to training noise-resilient concept detectors from clickthrough data collected by image search engines. We take advantage of the query logs to automatically produce concept detector training sets; these suffer though from label noise, i.e., erroneously assigned labels. We explore two alternative approaches for handling noisy training data at the classifier level by training concept detectors with two SVM variants: the Fuzzy SVM and the Power SVM. Experimental results on images collected from a professional image search engine indicate that 1) Fuzzy SVM outperforms both SVM and Power SVM and is the most effective approach towards handling label noise and 2) the performance gain of Fuzzy SVM compared to SVM increases progressively with the noise level in the training sets.}} (C) Theodora Tsikrika and Christos Diou "Multi-evidence User Group Discovery in Professional Image Search" Advances in Information Retrieval: 36th European Conference on IR Research, ECIR 2014, Amsterdam, The Netherlands, April 13-16, 2014., pp. 693-699, Springer International Publishing, Cham, 2014 Apr [Abstract][BibTex][pdf]This work evaluates the combination of multiple evidence for discovering groups of users with similar interests. User groups are created by analysing the search logs recorded for a sample of 149 users of a professional image search engine in conjunction with the textual and visual features of the clicked images, and evaluated by exploiting their topical classification. The results indicate that the discovered user groups are meaningful and that combining textual and visual features improves the homogeneity of the user groups compared to each individual feature.@inproceedings{Tsikrika2014Multi,author={Theodora Tsikrika and Christos Diou},title={Multi-evidence User Group Discovery in Professional Image Search},booktitle={Advances in Information Retrieval: 36th European Conference on IR Research, ECIR 2014, Amsterdam, The Netherlands, April 13-16, 2014.},pages={693-699},publisher={Springer International Publishing},address={Cham},year={2014},month={04},date={2014-04-13},url={http://dx.doi.org/10.1007/978-3-319-06028-6_78},doi={http://10.1007/978-3-319-06028-6_78},abstract={This work evaluates the combination of multiple evidence for discovering groups of users with similar interests. User groups are created by analysing the search logs recorded for a sample of 149 users of a professional image search engine in conjunction with the textual and visual features of the clicked images, and evaluated by exploiting their topical classification. The results indicate that the discovered user groups are meaningful and that combining textual and visual features improves the homogeneity of the user groups compared to each individual feature.}}

### 2013

 (J) Nikolaos Dimitriou and Anastasios Delopoulos "Motion-based segmentation of objects using overlapping temporal windows" Image and Vision Computing, 31, (9), pp. 593-602, 2013 Sep [Abstract][BibTex][pdf]Motion segmentation refers to the problem of separating the objects in a video sequence according to their motion. It is a fundamental problem of computer vision, since various systems focusing on the analysis of dynamic scenes include motion segmentation algorithms. In this paper we present a novel approach, where a video shot is temporally divided in successive and overlapping windows and motion segmentation is performed on each window respectively. This attribute renders the algorithm suitable even for long video sequences. In the last stage of the algorithm the segmentation results for every window are aggregated into a final segmentation. The presented algorithm can handle effectively asynchronous trajectories on each window even when they have no temporal intersection. The evaluation of the proposed algorithm on the Berkeley motion segmentation benchmark demonstrates its scalability and accuracy compared to the state of the art.@article{Dimitriou2013Motion,author={Nikolaos Dimitriou and Anastasios Delopoulos},title={Motion-based segmentation of objects using overlapping temporal windows},journal={Image and Vision Computing},volume={31},number={9},pages={593-602},year={2013},month={09},date={2013-09-01},url={http://www.sciencedirect.com/science/article/pii/S0262885613000929},doi={http://10.1016/j.imavis.2013.06.005},abstract={Motion segmentation refers to the problem of separating the objects in a video sequence according to their motion. It is a fundamental problem of computer vision, since various systems focusing on the analysis of dynamic scenes include motion segmentation algorithms. In this paper we present a novel approach, where a video shot is temporally divided in successive and overlapping windows and motion segmentation is performed on each window respectively. This attribute renders the algorithm suitable even for long video sequences. In the last stage of the algorithm the segmentation results for every window are aggregated into a final segmentation. The presented algorithm can handle effectively asynchronous trajectories on each window even when they have no temporal intersection. The evaluation of the proposed algorithm on the Berkeley motion segmentation benchmark demonstrates its scalability and accuracy compared to the state of the art.}} (J) Christos Maramis, Manolis Falelakis, Irini Lekka, Christos Diou, Pericles Mitkas and Anastasios Delopoulos "Applying semantic technologies in cervical cancer research" Data & Knowledge Engineering, 86, pp. 160-178, 2013 Jul [Abstract][BibTex][pdf]In this paper we present a research system that follows a semantic approach to facilitate medical association studies in the area of cervical cancer. Our system, named \\{ASSIST\\ and developed as an \\{EU\\ research project, assists in cervical cancer research by unifying multiple patient record repositories, physically located in different medical centers or hospitals. Semantic modeling of medical data and rules for inferring domain-specific information allow the system to (i) homogenize the information contained in the isolated repositories by translating it into the terms of a unified semantic representation, (ii) extract diagnostic information not explicitly stored in the individual repositories, and (iii) automate the process of evaluating medical hypotheses by performing case–control association studies, which is the ultimate goal of the system.@article{Maramis2013Applying,author={Christos Maramis and Manolis Falelakis and Irini Lekka and Christos Diou and Pericles Mitkas and Anastasios Delopoulos},title={Applying semantic technologies in cervical cancer research},journal={Data & Knowledge Engineering},volume={86},pages={160-178},year={2013},month={07},date={2013-07-01},url={http://www.sciencedirect.com/science/article/pii/S0169023X13000220},doi={http://10.1016/j.datak.2013.02.003},abstract={In this paper we present a research system that follows a semantic approach to facilitate medical association studies in the area of cervical cancer. Our system, named \\\\{ASSIST\\\\ and developed as an \\\\{EU\\\\ research project, assists in cervical cancer research by unifying multiple patient record repositories, physically located in different medical centers or hospitals. Semantic modeling of medical data and rules for inferring domain-specific information allow the system to (i) homogenize the information contained in the isolated repositories by translating it into the terms of a unified semantic representation, (ii) extract diagnostic information not explicitly stored in the individual repositories, and (iii) automate the process of evaluating medical hypotheses by performing case–control association studies, which is the ultimate goal of the system.}}

### 2013

 (C) Antonios Chrysopoulos, Christos Diou, Andreas L. Symeonidis and Pericles A. Mitkas "Agent-Based Small-Scale Energy Consumer Models for Energy Portfolio Management" International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013 IEEE/WIC/ACM, pp. 94-101, IEEE, 2013 Nov [Abstract][BibTex][pdf]In contemporary power systems, residential consumers may account for up to 50% of a country\'s total electrical energy consumption. Even though they constitute a significant portion of the energy market, not much has been achieved towards eliminating the inability for energy suppliers to perform long-term portfolio management, thus maximizing their revenue. The root cause of these problems is the difficulty in modeling consumers\' behavior, based on their everyday activities and personal comfort. If one were able to provide targeted incentives based on consumer profiles, the expected impact and market benefits would be significant. This paper introduces a formal residential consumer modeling methodology, that allows (i) the decomposition of the observed electrical load curves into consumer activities and, (ii) the evaluation of the impact of behavioral changes on the household\'s aggregate load curve. Analyzing electrical consumption measurements from DEHEMS research project enabled the model extraction of real-life consumers. Experiments indicate that the proposed methodology produces accurate small-scale consumer models and verify that small shifts in appliance usage times are sufficient to achieve significant peak power reduction.@inproceedings{Chrysopoulos2013Agent,author={Antonios Chrysopoulos and Christos Diou and Andreas L. Symeonidis and Pericles A. Mitkas},title={Agent-Based Small-Scale Energy Consumer Models for Energy Portfolio Management},booktitle={International Joint Conferences on Web Intelligence (WI) and Intelligent Agent Technologies (IAT), 2013 IEEE/WIC/ACM},pages={94-101},publisher={IEEE},year={2013},month={11},date={2013-11-17},url={http://dx.doi.org/10.1109/WI-IAT.2013.96},doi={http://10.1109/WI-IAT.2013.96},abstract={In contemporary power systems, residential consumers may account for up to 50% of a country\\'s total electrical energy consumption. Even though they constitute a significant portion of the energy market, not much has been achieved towards eliminating the inability for energy suppliers to perform long-term portfolio management, thus maximizing their revenue. The root cause of these problems is the difficulty in modeling consumers\\' behavior, based on their everyday activities and personal comfort. If one were able to provide targeted incentives based on consumer profiles, the expected impact and market benefits would be significant. This paper introduces a formal residential consumer modeling methodology, that allows (i) the decomposition of the observed electrical load curves into consumer activities and, (ii) the evaluation of the impact of behavioral changes on the household\\'s aggregate load curve. Analyzing electrical consumption measurements from DEHEMS research project enabled the model extraction of real-life consumers. Experiments indicate that the proposed methodology produces accurate small-scale consumer models and verify that small shifts in appliance usage times are sufficient to achieve significant peak power reduction.}}

### 2012

 (C) Georgios T. Andreou, Andreas L. Symeonidis, Christos Diou, Pericles A. Mitkas and Dimitrios P. Labridis "A framework for the implementation of large scale Demand Response" 2012 International Conference on Smart Grid Technology, Economics and Policies (SG-TEP), pp. 1-4, IEEE, 2012 Dec [Abstract][BibTex][pdf]The rationalization of electrical energy consumption is a constant goal driving research over the last decades. The pursuit of efficient solutions requires the involvement of electrical energy consumers through Demand Response programs. In this study, a framework is presented that can serve as a tool for designing and simulating Demand Response programs, aiming at energy efficiency through consumer behavioral change. It provides the capability to dynamically model groups of electrical energy consumers with respect to their consumption, as well as their behavior. This framework is currently under development within the scope of the EU funded FP7 project “CASSANDRA - A multivariate platform for assessing the impact of strategic decisions in electrical power systems”.@inproceedings{Andreou2012Framework,author={Georgios T. Andreou and Andreas L. Symeonidis and Christos Diou and Pericles A. Mitkas and Dimitrios P. Labridis},title={A framework for the implementation of large scale Demand Response},booktitle={2012 International Conference on Smart Grid Technology, Economics and Policies (SG-TEP)},pages={1-4},publisher={IEEE},year={2012},month={12},date={2012-12-03},url={http://dx.doi.org/10.1109/SG-TEP.2012.6642380},doi={http://10.1109/SG-TEP.2012.6642380},abstract={The rationalization of electrical energy consumption is a constant goal driving research over the last decades. The pursuit of efficient solutions requires the involvement of electrical energy consumers through Demand Response programs. In this study, a framework is presented that can serve as a tool for designing and simulating Demand Response programs, aiming at energy efficiency through consumer behavioral change. It provides the capability to dynamically model groups of electrical energy consumers with respect to their consumption, as well as their behavior. This framework is currently under development within the scope of the EU funded FP7 project “CASSANDRA - A multivariate platform for assessing the impact of strategic decisions in electrical power systems”.}}

### 2012

 (I) Christos Maramis, Dimitrios Karagiannis and Anastasios Delopoulos "HPVTyper: A Software Application for Automatic HPV Typing via PCR-RFLP Gel Electrophoresis" Charpter:16, 29, pp. 01, InTech, 2012 Jan [Abstract][BibTex][pdf]The quantitative information extraction from PCR-RFLP gel electrophoresis images requires the efficient modeling of the lane intensity profiles. To improve the acquired modeling accuracy, we introduce two novel ideas that can be incorporated in the modeling process. The first one proposes the use of the simplified integrated Weibull function as the basis function of the employed superposition model and the second proposes switching the domain of the intensity profile tobe-modeled to the unexploited fragment length domain.@inbook{Maramis2012HPVTyper,author={Christos Maramis and Dimitrios Karagiannis and Anastasios Delopoulos},title={HPVTyper: A Software Application for Automatic HPV Typing via PCR-RFLP Gel Electrophoresis},chapter={16},volume={29},pages={01},publisher={InTech},year={2012},month={01},date={2012-01-01},url={http://10.5772/28645},doi={http://10.1007/978-3-642-13039-7_169},abstract={The quantitative information extraction from PCR-RFLP gel electrophoresis images requires the efficient modeling of the lane intensity profiles. To improve the acquired modeling accuracy, we introduce two novel ideas that can be incorporated in the modeling process. The first one proposes the use of the simplified integrated Weibull function as the basis function of the employed superposition model and the second proposes switching the domain of the intensity profile tobe-modeled to the unexploited fragment length domain.}}

### 2011

 (J) Christos Maramis, Anastasios Delopoulos and Alexandros Lambropoulos "A Computerized Methodology for Improved Virus Typing by PCR-RFLP Gel Electrophoresis" IEEE Transactions on Biomedical Engineering, 58, (8), pp. 2339-2351, 2011 Aug [Abstract][BibTex][pdf]The analysis of digitized images from polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) gel electrophoresis examinations is a popular method for virus typing, i.e., for identifying the virus type(s) that have infected an investigated biological sample. However, being mostly manual, the conventional virus typing protocol remains laborious, time consuming, and error prone. In order to overcome these shortcomings, we propose a computerized methodology for improving virus typing via PCR-RFLP gel electrophoresis. A novel realistic observation model of the viral DNA motion on the gel matrix is employed to assist in exploiting additional virus-related information in comparison to the conventional approaches. The extracted rich information is fed to a novel typing algorithm, resulting in faster and more accurate decisions. The proposed methodology is evaluated for the case of the human papillomavirus typing on a dataset of 80 real and 1500 simulated samples, producing very satisfactory results.@article{Maramis2011Computerized,author={Christos Maramis and Anastasios Delopoulos and Alexandros Lambropoulos},title={A Computerized Methodology for Improved Virus Typing by PCR-RFLP Gel Electrophoresis},journal={IEEE Transactions on Biomedical Engineering},volume={58},number={8},pages={2339-2351},year={2011},month={08},date={2011-08-01},url={http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5765663},doi={http://10.1109/TBME.2011.2153202},abstract={The analysis of digitized images from polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) gel electrophoresis examinations is a popular method for virus typing, i.e., for identifying the virus type(s) that have infected an investigated biological sample. However, being mostly manual, the conventional virus typing protocol remains laborious, time consuming, and error prone. In order to overcome these shortcomings, we propose a computerized methodology for improving virus typing via PCR-RFLP gel electrophoresis. A novel realistic observation model of the viral DNA motion on the gel matrix is employed to assist in exploiting additional virus-related information in comparison to the conventional approaches. The extracted rich information is fed to a novel typing algorithm, resulting in faster and more accurate decisions. The proposed methodology is evaluated for the case of the human papillomavirus typing on a dataset of 80 real and 1500 simulated samples, producing very satisfactory results.}} (J) Christos Maramis and Anastasios Delopoulos "A Novel Algorithm for Restricting the Complexity of Virus Typing via PCR-RFLP Gel Electrophoresis" Biomedical Engineering Letters, 1, (4), pp. 239-246, 2011 Nov [Abstract][BibTex][pdf]PCR-RFLP gel electrophoresis is a popular method for virus typing (i.e., for identifying the types of a virus that have infected a biological sample), which has been automated recently owing to a computerized typing methodology. However, even with the help of this methodology, the PCRRFLP method suffers from low throughput, when compared to other typing methods. In this paper, we tackle this issue by introducing a novel algorithm for conducting the most computationally demanding phase of the aforementioned typing methodology (testing phase).@article{Maramis2011Novel,author={Christos Maramis and Anastasios Delopoulos},title={A Novel Algorithm for Restricting the Complexity of Virus Typing via PCR-RFLP Gel Electrophoresis},journal={Biomedical Engineering Letters},volume={1},number={4},pages={239-246},year={2011},month={11},date={2011-11-20},url={http://dx.doi.org/10.1007/s13534-011-0038-3},doi={http://10.1007/s13534-011-0038-3},abstract={PCR-RFLP gel electrophoresis is a popular method for virus typing (i.e., for identifying the types of a virus that have infected a biological sample), which has been automated recently owing to a computerized typing methodology. However, even with the help of this methodology, the PCRRFLP method suffers from low throughput, when compared to other typing methods. In this paper, we tackle this issue by introducing a novel algorithm for conducting the most computationally demanding phase of the aforementioned typing methodology (testing phase).}}

### 2011

 (C) Christos F. Maramis, Anastasios N. Delopoulos, Alexandros F. Lambropoulos and Sokratis P. Katafigiotis "A system for automatic HPV typing via PCR-RFLP gel electrophoresis" 2011 IEEE Conference on Automation Science and Engineering (CASE), pp. 549-556, IEEE, 2011 Aug [Abstract][BibTex][pdf]The identification of the types of the human papillomavirus (HPV) that have infected a female patient provides valuable information as regards to her risk for developing cervical cancer. A widely used method for performing the above task (namely HPV typing) is PCR-RFLP gel electrophoresis. However, the conventional HPV typing protocol is error-prone and resource-ineffective due to lack of interaction between the phases involved in it. In order to treat these shortcomings, we introduce a novel HPV typing system that can be built upon widely available laboratory equipment. The proposed workflow of the system automates the task of HPV typing via PCRRFLP gel electrophoresis. The proof-of-concept of the proposed methodology is evaluated via an experiment that emulates the operation of the introduced system on a set of real HPV data.@inproceedings{Maramis2011System,author={Christos F. Maramis and Anastasios N. Delopoulos and Alexandros F. Lambropoulos and Sokratis P. Katafigiotis},title={A system for automatic HPV typing via PCR-RFLP gel electrophoresis},booktitle={2011 IEEE Conference on Automation Science and Engineering (CASE)},pages={549-556},publisher={IEEE},year={2011},month={08},date={2011-08-14},url={http://mug.ee.auth.gr/wp-content/uploads/publications/06042466.pd},doi={http://10.1109/CASE.2011.6042466},abstract={The identification of the types of the human papillomavirus (HPV) that have infected a female patient provides valuable information as regards to her risk for developing cervical cancer. A widely used method for performing the above task (namely HPV typing) is PCR-RFLP gel electrophoresis. However, the conventional HPV typing protocol is error-prone and resource-ineffective due to lack of interaction between the phases involved in it. In order to treat these shortcomings, we introduce a novel HPV typing system that can be built upon widely available laboratory equipment. The proposed workflow of the system automates the task of HPV typing via PCRRFLP gel electrophoresis. The proof-of-concept of the proposed methodology is evaluated via an experiment that emulates the operation of the introduced system on a set of real HPV data.}}

### 2010

 (J) Christos Diou, George Stephanopoulos, Panagiotis Panagiotopoulos, Christos Papachristou, Nikos Dimitriou and Anastasios Delopoulos "Large-Scale Concept Detection in Multimedia Data Using Small Training Sets and Cross-Domain Concept Fusion" IEEE Transactions on Circuits and Systems for Video Technology, 20, (12), pp. 1808 - 1821, 2010 Oct [Abstract][BibTex][pdf]This paper presents the concept detector module developed for the VITALAS multimedia retrieval system. It outlines its architecture and major implementation aspects, including a set of procedures and tools that were used for the development of detectors for more than 500 concepts. The focus is on aspects that increase the system\'s scalability in terms of the number of concepts: collaborative concept definition and disambiguation, selection of small but sufficient training sets and efficient manual annotation. The proposed architecture uses cross-domain concept fusion to improve effectiveness and reduce the number of samples required for concept detector training. Two criteria are proposed for selecting the best predictors to use for fusion and their effectiveness is experimentally evaluated for 221 concepts on the TRECVID-2005 development set and 132 concepts on a set of images provided by the Belga news agency. In these experiments, cross-domain concept fusion performed better than early fusion for most concepts. Experiments with variable training set sizes also indicate that cross-domain concept fusion is more effective than early fusion when the training set size is small.@article{Diou2011Large,author={Christos Diou and George Stephanopoulos and Panagiotis Panagiotopoulos and Christos Papachristou and Nikos Dimitriou and Anastasios Delopoulos},title={Large-Scale Concept Detection in Multimedia Data Using Small Training Sets and Cross-Domain Concept Fusion},journal={IEEE Transactions on Circuits and Systems for Video Technology},volume={20},number={12},pages={1808 - 1821},year={2010},month={10},date={2010-10-18},url={http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=5604666},doi={http://10.1109/TCSVT.2010.2087814},abstract={This paper presents the concept detector module developed for the VITALAS multimedia retrieval system. It outlines its architecture and major implementation aspects, including a set of procedures and tools that were used for the development of detectors for more than 500 concepts. The focus is on aspects that increase the system\\'s scalability in terms of the number of concepts: collaborative concept definition and disambiguation, selection of small but sufficient training sets and efficient manual annotation. The proposed architecture uses cross-domain concept fusion to improve effectiveness and reduce the number of samples required for concept detector training. Two criteria are proposed for selecting the best predictors to use for fusion and their effectiveness is experimentally evaluated for 221 concepts on the TRECVID-2005 development set and 132 concepts on a set of images provided by the Belga news agency. In these experiments, cross-domain concept fusion performed better than early fusion for most concepts. Experiments with variable training set sizes also indicate that cross-domain concept fusion is more effective than early fusion when the training set size is small.}} (J) Theodora Tsikrika, Christos Diou, Arjen P. de Vries and Anastasios Delopoulos "Reliability and effectiveness of clickthrough data for automatic image annotation" Multimedia Tools and Applications, 55, (1), pp. 27-52, 2010 Aug [Abstract][BibTex][pdf]Automatic image annotation using supervised learning is performed by concept classifiers trained on labelled example images. This work proposes the use of clickthrough data collected from search logs as a source for the automatic generation of concept training data, thus avoiding the expensive manual annotation effort. We investigate and evaluate this approach using a collection of 97,628 photographic images. The results indicate that the contribution of search log based training data is positive despite their inherent noise; in particular, the combination of manual and automatically generated training data outperforms the use of manual data alone. It is therefore possible to use clickthrough data to perform large-scale image annotation with little manual annotation effort or, depending on performance, using only the automatically generated training data. An extensive presentation of the experimental results and the accompanying data can be accessed at http://olympus.ee.auth.gr/{\\textasciitildediou/civr2009/.@article{Tsikrika2011Reliability,author={Theodora Tsikrika and Christos Diou and Arjen P. de Vries and Anastasios Delopoulos},title={Reliability and effectiveness of clickthrough data for automatic image annotation},journal={Multimedia Tools and Applications},volume={55},number={1},pages={27-52},year={2010},month={08},date={2010-08-17},url={http://dx.doi.org/10.1007/s11042-010-0584-1},doi={http://10.1007/s11042-010-0584-1},abstract={Automatic image annotation using supervised learning is performed by concept classifiers trained on labelled example images. This work proposes the use of clickthrough data collected from search logs as a source for the automatic generation of concept training data, thus avoiding the expensive manual annotation effort. We investigate and evaluate this approach using a collection of 97,628 photographic images. The results indicate that the contribution of search log based training data is positive despite their inherent noise; in particular, the combination of manual and automatically generated training data outperforms the use of manual data alone. It is therefore possible to use clickthrough data to perform large-scale image annotation with little manual annotation effort or, depending on performance, using only the automatically generated training data. An extensive presentation of the experimental results and the accompanying data can be accessed at http://olympus.ee.auth.gr/{\\\\textasciitildediou/civr2009/.}}

### 2010

 (I) Christos Maramis and Anastasios Delopoulos "Improved Modeling of Lane Intensity Profiles on Gel Electrophoresis Images" Charpter:4, 29, pp. 671-674, Springer Berlin Heidelberg, 2010 May [Abstract][BibTex][pdf]The quantitative information extraction from PCR-RFLP gel electrophoresis images requires the efficient modeling of the lane intensity profiles. To improve the acquired modeling accuracy, we introduce two novel ideas that can be incorporated in the modeling process. The first one proposes the use of the simplified integrated Weibull function as the basis function of the employed superposition model and the second proposes switching the domain of the intensity profile tobe-modeled to the unexploited fragment length domain.@inbook{Maramis2010Improved,author={Christos Maramis and Anastasios Delopoulos},title={Improved Modeling of Lane Intensity Profiles on Gel Electrophoresis Images},chapter={4},volume={29},pages={671-674},publisher={Springer Berlin Heidelberg},year={2010},month={05},date={2010-05-27},url={http://mug.ee.auth.gr/wp-content/uploads/publications/chmaramisgelelec09.pdf},doi={http://10.1007/978-3-642-13039-7_169},abstract={The quantitative information extraction from PCR-RFLP gel electrophoresis images requires the efficient modeling of the lane intensity profiles. To improve the acquired modeling accuracy, we introduce two novel ideas that can be incorporated in the modeling process. The first one proposes the use of the simplified integrated Weibull function as the basis function of the employed superposition model and the second proposes switching the domain of the intensity profile tobe-modeled to the unexploited fragment length domain.}}

### 2009

 (J) Theodoros Agorastos, Vassilis Koutkias, Manolis Falelakis, Irini Lekka, Themistoklis Mikos, Anastasios Delopoulos, Pericles Mitkas, Antonios Tantsis, Steven Weyers, Pascal Coorevits, Andreas Kaufmann, Roberto Kurzeja and Nicos Maglaveras "Semantic Integration of Cervical Cancer Data Repositories to Facilitate Multicenter Association Studies: The ASSIST Approach" Cancer Informatics, 8, pp. 31-31, 2009 Jan [Abstract][BibTex][pdf]The current work addresses the unification of Electronic Health Records related to cervical cancer into a single medical knowledge source, in the context of the EU-funded ASSIST research project. The project aims to facilitate the research for cervical precancer and cancer through a system that virtually unifies multiple patient record repositories, physically located in different medical centers/hospitals, thus, increasing flexibility by allowing the formation of study groups \"on demand\" and by recycling patient records in new studies. To this end, ASSIST uses semantic technologies to translate all medical entities (such as patient examination results, history, habits, genetic profile) and represent them in a common form, encoded in the ASSIST Cervical Cancer Ontology. The current paper presents the knowledge elicitation approach followed, towards the definition and representation of the disease\'s medical concepts and rules that constitute the basis for the ASSIST Cervical Cancer Ontology. The proposed approach constitutes a paradigm for semantic integration of heterogeneous clinical data that may be applicable to other biomedical application domains.@article{Agorastos2009Semantic,author={Theodoros Agorastos and Vassilis Koutkias and Manolis Falelakis and Irini Lekka and Themistoklis Mikos and Anastasios Delopoulos and Pericles Mitkas and Antonios Tantsis and Steven Weyers and Pascal Coorevits and Andreas Kaufmann and Roberto Kurzeja and Nicos Maglaveras},title={Semantic Integration of Cervical Cancer Data Repositories to Facilitate Multicenter Association Studies: The ASSIST Approach},journal={Cancer Informatics},volume={8},pages={31-31},year={2009},month={01},date={2009-01-01},url={http://search.proquest.com/docview/1038326414?accountid=8359},abstract={The current work addresses the unification of Electronic Health Records related to cervical cancer into a single medical knowledge source, in the context of the EU-funded ASSIST research project. The project aims to facilitate the research for cervical precancer and cancer through a system that virtually unifies multiple patient record repositories, physically located in different medical centers/hospitals, thus, increasing flexibility by allowing the formation of study groups \\"on demand\\" and by recycling patient records in new studies. To this end, ASSIST uses semantic technologies to translate all medical entities (such as patient examination results, history, habits, genetic profile) and represent them in a common form, encoded in the ASSIST Cervical Cancer Ontology. The current paper presents the knowledge elicitation approach followed, towards the definition and representation of the disease\\'s medical concepts and rules that constitute the basis for the ASSIST Cervical Cancer Ontology. The proposed approach constitutes a paradigm for semantic integration of heterogeneous clinical data that may be applicable to other biomedical application domains.}}

### 2008

 (J) Manolis Falelakis, Christos Diou and Anastasios Delopoulos "Complexity control in semantic identification" International Journal of Intelligent Systems Technologies and Applications, 1, (3/4), pp. 247-262, 2008 Jan [Abstract][BibTex][pdf]This work introduces an efficient scheme for identifying semantic entities within multimedia data sets, providing mechanisms for modelling the trade-off between the accuracy of the result and the entailed computational cost. Semantic entities are described through formal definitions based on lower-level semantic and/or syntactic features. Based on appropriate metrics, the paper presents a methodology for selecting optimal subsets of syntactic features to extract, so that satisfactory results are obtained, while complexity remains below some required limit.@article{Falelakis2006Complexity,author={Manolis Falelakis and Christos Diou and Anastasios Delopoulos},title={Complexity control in semantic identification},journal={International Journal of Intelligent Systems Technologies and Applications},volume={1},number={3/4},pages={247-262},year={2008},month={01},date={2008-01-04},url={http://dx.doi.org/10.1504/IJISTA.2006.009907},doi={http://10.1504/IJISTA.2006.009907},abstract={This work introduces an efficient scheme for identifying semantic entities within multimedia data sets, providing mechanisms for modelling the trade-off between the accuracy of the result and the entailed computational cost. Semantic entities are described through formal definitions based on lower-level semantic and/or syntactic features. Based on appropriate metrics, the paper presents a methodology for selecting optimal subsets of syntactic features to extract, so that satisfactory results are obtained, while complexity remains below some required limit.}}

### 2008

 (I) Christos Diou, Nikos Batalas and Anastasios Delopoulos "Advances in Semantic Media Adaptation and Personalization" Charpter:Indexing and Browsing of Color Images: Design Considerations, 29, pp. 329-346, Springer, Berlin, Heidelberg, 2008 Jan [Abstract][BibTex][pdf]This chapter deals with the various problems and decisions associated with the design of a content based image retrieval system. Image descriptors and descriptor similarity measures, indexing data structures and navigation approaches are examined through the evaluation of a set representative methods. Insight is provided regarding their e?ciency and applicability. Furthermore the accuracy of using low dimensional FastMap point con?gurations for indexing is extensively evaluated through a set of experiments. While it is out of the scope of this chapter to o?er a review of state of the art techniques in the problems above, the results presented aim at assisting in the design and development of practical, usable and possibly large scale image databases.@inbook{Diou2008Indexing,author={Christos Diou and Nikos Batalas and Anastasios Delopoulos},title={Advances in Semantic Media Adaptation and Personalization},chapter={Indexing and Browsing of Color Images: Design Considerations},volume={29},pages={329-346},publisher={Springer},address={Berlin, Heidelberg},year={2008},month={01},date={2008-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/10.1007_978-3-540-76361_16.pdf},doi={http://10.1007/978-3-540-76361_16},abstract={This chapter deals with the various problems and decisions associated with the design of a content based image retrieval system. Image descriptors and descriptor similarity measures, indexing data structures and navigation approaches are examined through the evaluation of a set representative methods. Insight is provided regarding their e?ciency and applicability. Furthermore the accuracy of using low dimensional FastMap point con?gurations for indexing is extensively evaluated through a set of experiments. While it is out of the scope of this chapter to o?er a review of state of the art techniques in the problems above, the results presented aim at assisting in the design and development of practical, usable and possibly large scale image databases.}}

### 2007

 (J) Anatasios Delopoulos, Levon Sukissian and Stefanos Kollias "An efficient multiresolution texture classification scheme using neural networks" International Journal of Computer Mathematics, 67, (1-2), pp. 155-168, 2007 Mar [Abstract][BibTex][pdf]An efficient multiresolution texture classification method is proposed in this paper, based on 2-D linear prediction, multiresolution decomposition and artificial neural networks. A multiresolution spectral analysis of textured images is first developed, which permits 2-D AR texture modelling to be performed in multiple resolutions. Recursive estimation algorithms combined witth the Itakura distance measure provide sets of AR model parameters representing different textures at various resolutions. Appropriate neural network banks are constructed and trained being then able to effectively perform classification of textures irrespective of their resolution level. Results are presented using real textured images which illustrate the good performance of the proposed approach.@article{Delopoulos2007Efficient,author={Anatasios Delopoulos and Levon Sukissian and Stefanos Kollias},title={An efficient multiresolution texture classification scheme using neural networks},journal={International Journal of Computer Mathematics},volume={67},number={1-2},pages={155-168},year={2007},month={03},date={2007-03-20},url={http://mug.ee.auth.gr/wp-content/uploads/00207169808804657.pdf},doi={http://10.1080/00207169808804657},abstract={An efficient multiresolution texture classification method is proposed in this paper, based on 2-D linear prediction, multiresolution decomposition and artificial neural networks. A multiresolution spectral analysis of textured images is first developed, which permits 2-D AR texture modelling to be performed in multiple resolutions. Recursive estimation algorithms combined witth the Itakura distance measure provide sets of AR model parameters representing different textures at various resolutions. Appropriate neural network banks are constructed and trained being then able to effectively perform classification of textures irrespective of their resolution level. Results are presented using real textured images which illustrate the good performance of the proposed approach.}}

### 2006

 (J) Manolis Falelakis, Christos Diou and Anastasios Delopoulos "Semantic identification: balancing between complexity and validity" EURASIP Journal on Applied Signal Processing, pp. 183-183, 2006 Jan [Abstract][BibTex][pdf]An efficient scheme for identifying semantic entities within data sets such as multimedia documents, scenes, signals, and so forth, is proposed in this work. Expression of semantic entities in terms of syntactic properties is modelled with appropriately defined finite automata, which also model the identification procedure. Based on the structure and properties of these automata, formal definitions of attained validity and certainty and also required complexity are defined as metrics of identification efficiency. The main contribution of the paper relies on organizing the identification and search procedure in a way that maximizes its validity for bounded complexity budgets and reversely minimizes computational complexity for a given required validity threshold. The associated optimization problem is solved by using dynamic programming. Finally, a set of experiments provides insight to the introduced theoretical framework.@article{Falelakis2006Semantic,author={Manolis Falelakis and Christos Diou and Anastasios Delopoulos},title={Semantic identification: balancing between complexity and validity},journal={EURASIP Journal on Applied Signal Processing},pages={183-183},year={2006},month={01},date={2006-01-01},url={http://dx.doi.org/10.1155/ASP/2006/41716},doi={http://10.1155/ASP/2006/41716},abstract={An efficient scheme for identifying semantic entities within data sets such as multimedia documents, scenes, signals, and so forth, is proposed in this work. Expression of semantic entities in terms of syntactic properties is modelled with appropriately defined finite automata, which also model the identification procedure. Based on the structure and properties of these automata, formal definitions of attained validity and certainty and also required complexity are defined as metrics of identification efficiency. The main contribution of the paper relies on organizing the identification and search procedure in a way that maximizes its validity for bounded complexity budgets and reversely minimizes computational complexity for a given required validity threshold. The associated optimization problem is solved by using dynamic programming. Finally, a set of experiments provides insight to the introduced theoretical framework.}} (J) M. Wallace, T. Athanasiadis, Y. Avrithis, A. N. Delopoulos and S. Kollias "Integrating multimedia archives: the architecture and the content layer" IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans, 36, (1), pp. 34-52, 2006 Jan [Abstract][BibTex][pdf]In the last few years, numerous multimedia archives have made extensive use of digitized storage and annotation technologies. Still, the development of single points of access, providing common and uniform access to their data, despite the efforts and accomplishments of standardization organizations, has remained an open issue as it involves the integration of various large-scale heterogeneous and heterolingual systems. This paper describes a mediator system that achieves architectural integration through an extended three-tier architecture and content integration through semantic modeling. The described system has successfully integrated five multimedia archives, quite different in nature and content from each other, while also providing easy and scalable inclusion of more archives in the future.@article{Wallace2006Integrating,author={M. Wallace and T. Athanasiadis and Y. Avrithis and A. N. Delopoulos and S. Kollias},title={Integrating multimedia archives: the architecture and the content layer},journal={IEEE Transactions on Systems, Man, and Cybernetics - Part A: Systems and Humans},volume={36},number={1},pages={34-52},year={2006},month={01},date={2006-01-01},url={http://dx.doi.org/10.1109/TSMCA.2005.859184},doi={http://10.1109/TSMCA.2005.859184},abstract={In the last few years, numerous multimedia archives have made extensive use of digitized storage and annotation technologies. Still, the development of single points of access, providing common and uniform access to their data, despite the efforts and accomplishments of standardization organizations, has remained an open issue as it involves the integration of various large-scale heterogeneous and heterolingual systems. This paper describes a mediator system that achieves architectural integration through an extended three-tier architecture and content integration through semantic modeling. The described system has successfully integrated five multimedia archives, quite different in nature and content from each other, while also providing easy and scalable inclusion of more archives in the future.}}

### 2005

 (C) Niki Aifanti and Anastasios Delopoulos "Fuzzy-logic Based Information Fusion for Image Segmentation" IEEE International Conference on Image Processing 2005, 2005 Sep [Abstract][BibTex][pdf]This work presents an information fusion mechanism for image segmentation using multiple cues. Initially, a fuzzy clustering of each cue space is performed and corresponding membership functions are produced on the image coordinates space. The latter include complementary as well as redundant information. A fuzzy inference mechanism is developed, which exploits these characteristics and fuses the membership functions. The produced aggregate membership functions represent objects, which bear combinations of the properties specified by the cues. The segmented image results after post-processing and defuzzification, which involves majority voting. A fuzzy rule based merging algorithm is finally proposed for reducing possible oversegmentation. Experimental results have been included to illustrate the steps and the efficiency of the algorithm.@inproceedings{Aifanti2005Fuzzy,author={Niki Aifanti and Anastasios Delopoulos},title={Fuzzy-logic Based Information Fusion for Image Segmentation},booktitle={IEEE International Conference on Image Processing 2005},year={2005},month={09},date={2005-09-01},url={http://mug.ee.auth.gr/wp-content/uploads/publications/01530279.pdf},doi={http://10.1109/ICIP.2005.1530279},abstract={This work presents an information fusion mechanism for image segmentation using multiple cues. Initially, a fuzzy clustering of each cue space is performed and corresponding membership functions are produced on the image coordinates space. The latter include complementary as well as redundant information. A fuzzy inference mechanism is developed, which exploits these characteristics and fuses the membership functions. The produced aggregate membership functions represent objects, which bear combinations of the properties specified by the cues. The segmented image results after post-processing and defuzzification, which involves majority voting. A fuzzy rule based merging algorithm is finally proposed for reducing possible oversegmentation. Experimental results have been included to illustrate the steps and the efficiency of the algorithm.}} (C) Christos Diou, Manolis Falelakis and Anastasios Delopoulos "Knowledge Based Unification of Medical Archives" International Networking Conference (INC2005), Samos, Greece, 2005 Jan [Abstract][BibTex]@inproceedings{Diou2005Knowledge,author={Christos Diou and Manolis Falelakis and Anastasios Delopoulos},title={Knowledge Based Unification of Medical Archives},booktitle={International Networking Conference (INC2005)},address={Samos, Greece},year={2005},month={01},date={2005-01-01}} (C) Manolis Falelakis, Christos Diou, Anastasios Valsamidis and Anastasios Delopoulos "Complexity Control in Semantic Identification" IEEE International Conference on Fuzzy Systems (FUZZ-IEEE05), pp. 102-107, Reno, Nevada, USA, 2005 Jan [Abstract][BibTex][pdf]This paper proposes a methodology for modeling the process of semantic identification and controlling its complexity and accuracy of the results. Each semantic entity is defined in terms of lower level semantic entities and low level features that can be automatically extracted, while different membership degrees are assigned to each one of the entities participating in a definition, depending on their importance for the identification. By selecting only a subset of the features that are used to define a semantic entity both complexity and accuracy of the results are reduced. It is possible, however, to design the identification using the metrics introduced, so that satisfactory results are obtained, while complexity remains below some required limit.@inproceedings{Falelakis2005Complexity,author={Manolis Falelakis and Christos Diou and Anastasios Valsamidis and Anastasios Delopoulos},title={Complexity Control in Semantic Identification},booktitle={IEEE International Conference on Fuzzy Systems (FUZZ-IEEE05)},pages={102-107},address={Reno, Nevada, USA},year={2005},month={01},date={2005-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/Falelakis-Diou-Valsamidis-Delopoulos_FUZZIEEE05_paper1.pdf},doi={http://10.1504/IJISTA.2006.009907},abstract={This paper proposes a methodology for modeling the process of semantic identification and controlling its complexity and accuracy of the results. Each semantic entity is defined in terms of lower level semantic entities and low level features that can be automatically extracted, while different membership degrees are assigned to each one of the entities participating in a definition, depending on their importance for the identification. By selecting only a subset of the features that are used to define a semantic entity both complexity and accuracy of the results are reduced. It is possible, however, to design the identification using the metrics introduced, so that satisfactory results are obtained, while complexity remains below some required limit.}} (C) Manolis Falelakis, Christos Diou, Anastasios Valsamidis and Anastasios Delopoulos "Dynamic Semantic Identification with Complexity Constraints as a Knapsack Problem" The 14th IEEE International Conference on Fuzzy Systems, 2005. FUZZ '05., IEEE, 2005 May [Abstract][BibTex][pdf]The process of automatic identification of high level semantic entities (e.g., objects, concepts or events) in multimedia documents requires processing by means of algorithms that are used for feature extraction, i.e. low level information needed for the analysis of these documents at a semantic level. This work copes with the high and often prohibitive computational complexity of this procedure. Emphasis is given to a dynamic scheme that allows for efficient distribution of the available computational resources in application. Scenarios that deal with the identification of multiple high level entities with strict simultaneous restrictions, such as real time applications.@inproceedings{Falelakis2005Dynamic,author={Manolis Falelakis and Christos Diou and Anastasios Valsamidis and Anastasios Delopoulos},title={Dynamic Semantic Identification with Complexity Constraints as a Knapsack Problem},booktitle={The 14th IEEE International Conference on Fuzzy Systems, 2005. FUZZ '05.},publisher={IEEE},year={2005},month={05},date={2005-05-25},url={http://mug.ee.auth.gr/wp-content/uploads/Falelakis-Diou-Valsamidis-Delopoulos_FUZZIEEE05_paper2.pdf},doi={http://10.1109/FUZZY.2005.1452456},abstract={The process of automatic identification of high level semantic entities (e.g., objects, concepts or events) in multimedia documents requires processing by means of algorithms that are used for feature extraction, i.e. low level information needed for the analysis of these documents at a semantic level. This work copes with the high and often prohibitive computational complexity of this procedure. Emphasis is given to a dynamic scheme that allows for efficient distribution of the available computational resources in application. Scenarios that deal with the identification of multiple high level entities with strict simultaneous restrictions, such as real time applications.}} (C) Manolis Falelakis, Christos Diou, Manolis Wallace and Anastasios Delopoulos "Minimizing Uncertainty In Semantic Identification When Computing Resources Are Limited" International Conference on Artificial Neural Networks (ICANN05), pp. 817-822, Springer Berlin Heidelberg, Warsaw, Poland, 2005 Jan [Abstract][BibTex][pdf]In this paper we examine the problem of automatic semantic identi?cation of entities in multimedia documents from a computing point of view. Speci?cally, we identify as main points to consider the storage of the required knowledge and the computational complexity of the handling of the knowledge as well as of the actual identi?cation process. In order to tackle the above we utilize (i) a sparse representation model for storage, (ii) a novel transitive closure algorithm for handling and (iii) a novel approach to identi?cation that allows for the speci?cation of computational boundaries.@inproceedings{Falelakis2005Minimizing,author={Manolis Falelakis and Christos Diou and Manolis Wallace and Anastasios Delopoulos},title={Minimizing Uncertainty In Semantic Identification When Computing Resources Are Limited},booktitle={International Conference on Artificial Neural Networks (ICANN05)},pages={817-822},publisher={Springer Berlin Heidelberg},address={Warsaw, Poland},year={2005},month={01},date={2005-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/10.1007_11550907_129.pdf},doi={http://10.1007/11550907_129},abstract={In this paper we examine the problem of automatic semantic identi?cation of entities in multimedia documents from a computing point of view. Speci?cally, we identify as main points to consider the storage of the required knowledge and the computational complexity of the handling of the knowledge as well as of the actual identi?cation process. In order to tackle the above we utilize (i) a sparse representation model for storage, (ii) a novel transitive closure algorithm for handling and (iii) a novel approach to identi?cation that allows for the speci?cation of computational boundaries.}}

### 2005

 (I) Anastasios Delopoulos "Multimedia Coding Techniques for Wireless Networks" Charpter:2, 29, pp. 15-47, Wiley, 2005 Jan [Abstract][BibTex][pdf]This chapter deals with the various problems and decisions associated with the design of a content based image retrieval system. Image descriptors and descriptor similarity measures, indexing data structures and navigation approaches are examined through the evaluation of a set representative methods. Insight is provided regarding their e?ciency and applicability. Furthermore the accuracy of using low dimensional FastMap point con?gurations for indexing is extensively evaluated through a set of experiments. While it is out of the scope of this chapter to o?er a review of state of the art techniques in the problems above, the results presented aim at assisting in the design and development of practical, usable and possibly large scale image databases.@inbook{Delopoulos2005Multimedia,author={Anastasios Delopoulos},title={Multimedia Coding Techniques for Wireless Networks},chapter={2},volume={29},pages={15-47},publisher={Wiley},year={2005},month={01},date={2005-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/10.1007_978-3-540-76361_16.pdf},doi={http://10.1007/978-3-540-76361_16},abstract={This chapter deals with the various problems and decisions associated with the design of a content based image retrieval system. Image descriptors and descriptor similarity measures, indexing data structures and navigation approaches are examined through the evaluation of a set representative methods. Insight is provided regarding their e?ciency and applicability. Furthermore the accuracy of using low dimensional FastMap point con?gurations for indexing is extensively evaluated through a set of experiments. While it is out of the scope of this chapter to o?er a review of state of the art techniques in the problems above, the results presented aim at assisting in the design and development of practical, usable and possibly large scale image databases.}}

### 2004

 (C) Manolis Falelakis, Christos Diou and Anastasios Delopoulos "Identification of Semantics: Balancing between Complexity and Validity" 2004 IEEE 6th Workshop on Multimedia Signal Processing, pp. 434-437, IEEE, Siena, Italy, 2004 Sep [Abstract][BibTex][pdf]This paper addresses the problem of identifying semantic entities (e.g., events, objects, concepts etc.) in a particular environment (e.g., a multimedia document, a scene, a signal etc.) by means of an appropriately modelled semantic encyclopedia. Each semantic entity in the encyclopedia is defined in terms of other semantic entities as well as low level features, which we call syntactic entities, in a hierarchical scheme. Furthermore, a methodology is introduced, which can be used to evaluate the direct contribution of every syntactic feature of the document to the identification of semantic entities. This information allows us to estimate the quality of the result as well as the required computational cost of the search procedure and to balance between them. Our approach could be particularly important in real time and/or bulky search/indexing applications.@inproceedings{Falelakis2004Identification,author={Manolis Falelakis and Christos Diou and Anastasios Delopoulos},title={Identification of Semantics: Balancing between Complexity and Validity},booktitle={2004 IEEE 6th Workshop on Multimedia Signal Processing},pages={434-437},publisher={IEEE},address={Siena, Italy},year={2004},month={09},date={2004-09-29},url={http://mug.ee.auth.gr/wp-content/uploads/Falelakis-Diou-Delopoulos_MMSP04.pdf},doi={http://10.1109/MMSP.2004.1436588},abstract={This paper addresses the problem of identifying semantic entities (e.g., events, objects, concepts etc.) in a particular environment (e.g., a multimedia document, a scene, a signal etc.) by means of an appropriately modelled semantic encyclopedia. Each semantic entity in the encyclopedia is defined in terms of other semantic entities as well as low level features, which we call syntactic entities, in a hierarchical scheme. Furthermore, a methodology is introduced, which can be used to evaluate the direct contribution of every syntactic feature of the document to the identification of semantic entities. This information allows us to estimate the quality of the result as well as the required computational cost of the search procedure and to balance between them. Our approach could be particularly important in real time and/or bulky search/indexing applications.}} (C) Panagiotis Panagiotopoulos, Manolis Falelakis and Anastasios Delopoulos "Efficient Semantic Search Using Finite Automata" 6th COST 276 Workshop on Information and Knowledge Management for Integrated Media Communication, 2004 Jan [Abstract][BibTex][pdf]An efficient scheme for identifying Semantic Entities within data sets such as multimedia documents, scenes, signals etc. is proposed in this work. Expression of Semantic Entities in terms of Syntactic Properties is proved to be isomorphic to appropriately defined finite automata, which also model the identification procedure. Based on the structure and properties of these automata, formal definitions of attained Validity and Certainty and also required Complexity are defined as metrics of identification efficiency. The main contribution of the paper relies on organizing the identification and search procedure in a way that maximizes its validity for bounded Complexity budgets and reversely minimizes computational Complexity for a given required Validity threshold.@inproceedings{Panagiotopoulos2004Efficient,author={Panagiotis Panagiotopoulos and Manolis Falelakis and Anastasios Delopoulos},title={Efficient Semantic Search Using Finite Automata},booktitle={6th COST 276 Workshop on Information and Knowledge Management for Integrated Media Communication},year={2004},month={01},date={2004-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/panagiotopoulos-falelakis-delopoulos-cost276.pdf},abstract={An efficient scheme for identifying Semantic Entities within data sets such as multimedia documents, scenes, signals etc. is proposed in this work. Expression of Semantic Entities in terms of Syntactic Properties is proved to be isomorphic to appropriately defined finite automata, which also model the identification procedure. Based on the structure and properties of these automata, formal definitions of attained Validity and Certainty and also required Complexity are defined as metrics of identification efficiency. The main contribution of the paper relies on organizing the identification and search procedure in a way that maximizes its validity for bounded Complexity budgets and reversely minimizes computational Complexity for a given required Validity threshold.}}

### 2003

 (J) C. Diou, Karwatka and Jacek "Some methods of identification high clutter regions in radar tracking system" Postepy Radiotechniki, 48, (147), pp. 3-15, 2003 Jan [Abstract][BibTex]@article{Diou2003Some,author={C. Diou and Karwatka and Jacek},title={Some methods of identification high clutter regions in radar tracking system},journal={Postepy Radiotechniki},volume={48},number={147},pages={3-15},year={2003},month={01},date={2003-01-01}}

### 2000

 (J) Yiannis Xirouhakis and Anastasios Delopoulos "A Comparative Study on 3D Motion Estimation under Orthography" Nordic signal processing symposium, 2000 Jun [Abstract][BibTex][pdf]In the present work, the algorithm proposed in [8,10] is tested against existing approaches on 3D motion and structure estimation of rigid objects under orthography. The theoretical relation between the proposed approach and the well-known factorization and epipolar methods is discussed. At the same time, comparative simulated experiments are given, illustrating the performance of the three algorithms (the factorization, the epipolar and the proposed one). The proposed algorithm seems to be more genericthan the existing approaches, and provides superior estimates of 3D motion in most cases.@article{Xirouhakis2000Comparative,author={Yiannis Xirouhakis and Anastasios Delopoulos},title={A Comparative Study on 3D Motion Estimation under Orthography},journal={Nordic signal processing symposium},year={2000},month={06},date={2000-06-01},url={http://mug.ee.auth.gr/wp-content/uploads/publications/page057_id151.pdf},abstract={In the present work, the algorithm proposed in [8,10] is tested against existing approaches on 3D motion and structure estimation of rigid objects under orthography. The theoretical relation between the proposed approach and the well-known factorization and epipolar methods is discussed. At the same time, comparative simulated experiments are given, illustrating the performance of the three algorithms (the factorization, the epipolar and the proposed one). The proposed algorithm seems to be more genericthan the existing approaches, and provides superior estimates of 3D motion in most cases.}} (J) Yiannis Xirouhakis and Anastasios Delopoulos "Least Squares Estimation of 3D Shape and Motion of Rigid Objects from their Orthographic Projections" IEEE Transactions on Pattern Analysis and Machine Intelligence, 22, (4), pp. 393-399, 2000 Apr [Abstract][BibTex][pdf]The extraction of motion and shape information of three-dimensional objects from their two-dimensional projections is a task that emerges in various applications such as computer vision, biomedical engineering, and video coding and mining especially after the recent guidelines of the Motion Pictures Expert Group regarding MPEG-4 and MPEG-7 standards. Present work establishes a novel approach for extracting the motion and shape parameters of a rigid three-dimensional object on the basis of its orthographic projections and the associated motion field. Experimental results have been included to verify the theoretical analysis.@article{Xirouhakis2000Least,author={Yiannis Xirouhakis and Anastasios Delopoulos},title={Least Squares Estimation of 3D Shape and Motion of Rigid Objects from their Orthographic Projections},journal={IEEE Transactions on Pattern Analysis and Machine Intelligence},volume={22},number={4},pages={393-399},year={2000},month={04},date={2000-04-01},url={http://dx.doi.org/10.1109/34.845382},doi={http://10.1109/34.845382},abstract={The extraction of motion and shape information of three-dimensional objects from their two-dimensional projections is a task that emerges in various applications such as computer vision, biomedical engineering, and video coding and mining especially after the recent guidelines of the Motion Pictures Expert Group regarding MPEG-4 and MPEG-7 standards. Present work establishes a novel approach for extracting the motion and shape parameters of a rigid three-dimensional object on the basis of its orthographic projections and the associated motion field. Experimental results have been included to verify the theoretical analysis.}}

### 1999

 (J) Sotirios Pavlopoulos and Anastasios Delopoulos "Designing and implementing the transition to a fully digital hospital" IEEE Transactions on Information Technology in Biomedicine, 3, (1), pp. 6-19, 1999 Mar [Abstract][BibTex][pdf]The increase in the number of examinations performed in modern healthcare institutions in conjunction with the range of imaging modalities available today have resulted in a tremendous increase in the number of medical images generated and has made the need for a dedicated system able to acquire, distribute, and store medical image data very attractive. Within the framework of the Hellenic R&D program, we have designed and implemented a picture archiving and communication system for a high-tech cardiosurgery hospital in Greece. The system is able to handle in a digital form images produced from ultrasound, X-ray angiography, ?-camera, chest X-rays, as well as electrocardiogram signals. Based on the adoption of an open architecture highly relying on the DICOM standard, the system enables the smooth transition from the existing procedures to a fully digital operation mode and the integration of all existing medical equipment to the new central archiving system.@article{Pavlopoulos1999Designing,author={Sotirios Pavlopoulos and Anastasios Delopoulos},title={Designing and implementing the transition to a fully digital hospital},journal={IEEE Transactions on Information Technology in Biomedicine},volume={3},number={1},pages={6-19},year={1999},month={03},date={1999-03-01},url={http://dx.doi.org/10.1109/4233.748971},doi={http://10.1109/4233.748971},abstract={The increase in the number of examinations performed in modern healthcare institutions in conjunction with the range of imaging modalities available today have resulted in a tremendous increase in the number of medical images generated and has made the need for a dedicated system able to acquire, distribute, and store medical image data very attractive. Within the framework of the Hellenic R&D program, we have designed and implemented a picture archiving and communication system for a high-tech cardiosurgery hospital in Greece. The system is able to handle in a digital form images produced from ultrasound, X-ray angiography, ?-camera, chest X-rays, as well as electrocardiogram signals. Based on the adoption of an open architecture highly relying on the DICOM standard, the system enables the smooth transition from the existing procedures to a fully digital operation mode and the integration of all existing medical equipment to the new central archiving system.}}

### 1999

 (C) Yiannis Xirouhakis, George Votsis and Anastasios Delopoulos "Estimation of 3D Motion and Structure of Human Faces" Advances in Intelligent Systems: Concepts, Tools and Applications, pp. 333-344, Springer Netherlands, 1999 Jan [Abstract][BibTex][pdf]The extraction of motion and shape information of three dimensional objects from video sequences emerges in various applications especially within the framework of the MPEG-4 and MPEG-7 standards. Particular attention has been given to this problem within the scope of model-based coding and knowledge-based ZD modeling. In this chapter, a novel algorithm is proposed for the 3D reconstruction of a human face from 2D projections. The obtained results can contribute to several fields with an emphasis on 3D modeling and characterization of human faces.@inproceedings{Xirouhakis1999Estimation,author={Yiannis Xirouhakis and George Votsis and Anastasios Delopoulos},title={Estimation of 3D Motion and Structure of Human Faces},booktitle={Advances in Intelligent Systems: Concepts, Tools and Applications},pages={333-344},publisher={Springer Netherlands},year={1999},month={01},date={1999-01-01},url={http://dx.doi.org/10.1007/978-94-011-4840-5_30},doi={http://10.1007/978-94-011-4840-5_30},abstract={The extraction of motion and shape information of three dimensional objects from video sequences emerges in various applications especially within the framework of the MPEG-4 and MPEG-7 standards. Particular attention has been given to this problem within the scope of model-based coding and knowledge-based ZD modeling. In this chapter, a novel algorithm is proposed for the 3D reconstruction of a human face from 2D projections. The obtained results can contribute to several fields with an emphasis on 3D modeling and characterization of human faces.}} (C) Yiannis Xirouhakis, Gabriel Tsechpenakis and Anastasios Delopoulos "User Choices for Efficient 3D Motion and Shape Extraction from Orthographic Projections" The 6th IEEE International Conference on Electronics, Circuits and Systems, 1999. Proceedings of ICECS '99, pp. 1261- 264, Pafos, 1999 Sep [Abstract][BibTex][pdf]The extraction of structure-from-motion emerges in several research fields such as computer vision, video coding, biomedical engineering and human-computer interaction. The present work focuses on the algorithmic approach of structure-from-motion extraction under orthography providing, at the same time, guidelines in matters of implementation. Relative principles, constraints and stability are discussed. The improvement of the algorithm\'s performance w.r.t. the proposed user-choices is illustrated by means of experimental results.@inproceedings{Xirouhakis1999User,author={Yiannis Xirouhakis and Gabriel Tsechpenakis and Anastasios Delopoulos},title={User Choices for Efficient 3D Motion and Shape Extraction from Orthographic Projections},booktitle={The 6th IEEE International Conference on Electronics, Circuits and Systems, 1999. Proceedings of ICECS '99},pages={1261- 264},address={Pafos},year={1999},month={09},date={1999-09-05},url={http://mug.ee.auth.gr/wp-content/uploads/publications/00814398.pdf},doi={http://10.1109/ICECS.1999.814398},abstract={The extraction of structure-from-motion emerges in several research fields such as computer vision, video coding, biomedical engineering and human-computer interaction. The present work focuses on the algorithmic approach of structure-from-motion extraction under orthography providing, at the same time, guidelines in matters of implementation. Relative principles, constraints and stability are discussed. The improvement of the algorithm\\'s performance w.r.t. the proposed user-choices is illustrated by means of experimental results.}}

### 1998

 (J) Stefanos Kollias and Anastasios Delopoulos "Multiresolution Techniques and their Applications to Image Recognition" Expert Systems Techniques and Applications, 1998 Jan [Abstract][BibTex]@article{Kollias1998Multiresolution,author={Stefanos Kollias and Anastasios Delopoulos},title={Multiresolution Techniques and their Applications to Image Recognition},journal={Expert Systems Techniques and Applications},year={1998},month={01},date={1998-01-01}}

### 1998

 (C) Yannis S. Avrithis, Anastasios N. Delopoulos and Vassilios N. Alexopoulos "Ultrasonic Array Imaging Using CDMA Techniques" 9th European Signal Processing Conference (EUSIPCO 1998), Rhodes, 1998 Sep [Abstract][BibTex][pdf]A new method for designing ultrasonic imaging systems is presented in this paper. The method is based on the use of transducer arrays whose elements transmit wideband signals generated by pseudo-random codes, similarly to code division multiple access (CDMA) systems in communications. The use of code sequences instead of pulses, which are typically used in conventional phased arrays, combined with transmit and receive beamforming for steering different codes at each direction, permits parallel acquisition of a large number of measurements corresponding to different directions. Significantly higher image acquisition rate as well as lateral and contrast resolution are thus obtained, while axial resolution remains close to that of phased arrays operating in pulse-echo mode. Time and frequency division techniques are also studied and a unified theoretical model is derived, which is validated by experimental results.@inproceedings{Avrithis1998Ultrasonic,author={Yannis S. Avrithis and Anastasios N. Delopoulos and Vassilios N. Alexopoulos},title={Ultrasonic Array Imaging Using CDMA Techniques},booktitle={9th European Signal Processing Conference (EUSIPCO 1998)},address={Rhodes},year={1998},month={09},date={1998-09-08},url={http://mug.ee.auth.gr/wp-content/uploads/Ultrasonic-Array-Imaging-Using-CDMA-Techniques-Y.-Avrithis1998.pdf},abstract={A new method for designing ultrasonic imaging systems is presented in this paper. The method is based on the use of transducer arrays whose elements transmit wideband signals generated by pseudo-random codes, similarly to code division multiple access (CDMA) systems in communications. The use of code sequences instead of pulses, which are typically used in conventional phased arrays, combined with transmit and receive beamforming for steering different codes at each direction, permits parallel acquisition of a large number of measurements corresponding to different directions. Significantly higher image acquisition rate as well as lateral and contrast resolution are thus obtained, while axial resolution remains close to that of phased arrays operating in pulse-echo mode. Time and frequency division techniques are also studied and a unified theoretical model is derived, which is validated by experimental results.}} (C) Anastasios Delopoulos, Yiannis XirouhakisRobust Estimation of Motion and Shape based on Orthographic Projections of Rigid Objects "Robust Estimation of Motion and Shape based on Orthographic Projections of Rigid Objects" IEEE Tenth Image and Multidimensional Signal Processing Workshop - IMDSP'98, IEEE, 1998 Jan [Abstract][BibTex]@inproceedings{Delopoulos1998Robust,author={Anastasios Delopoulos and Yiannis XirouhakisRobust Estimation of Motion and Shape based on Orthographic Projections of Rigid Objects},title={Robust Estimation of Motion and Shape based on Orthographic Projections of Rigid Objects},booktitle={IEEE Tenth Image and Multidimensional Signal Processing Workshop - IMDSP'98},publisher={IEEE},year={1998},month={01},date={1998-01-01}} (C) Anastasios Doulamis, Nikolaos Doulamis and Anastasios Delopoulos "Optimal Subband Analysis Filters Compensating for Quantization and Additive Noise" 9th European Signal Processing Conference (EUSIPCO 1998, IEEE, Rhodes, 1998 Sep [Abstract][BibTex][pdf]In this paper, we present an analysis filter design technique which optimally defines the proper decimator so that the quantization noise is compensated. The analysis is based on a distortion criterion minimization using the Lagrange multipliers. The optimal decimation filters are derived through a Ricatti solution which involves both the quantization and the interpolation filters. Experimental results are presented indicating the good performance of the proposed technique versus conventional subband filter banks in the presence of quantization noise.@inproceedings{Doulamis1998Optimal,author={Anastasios Doulamis and Nikolaos Doulamis and Anastasios Delopoulos},title={Optimal Subband Analysis Filters Compensating for Quantization and Additive Noise},booktitle={9th European Signal Processing Conference (EUSIPCO 1998},publisher={IEEE},address={Rhodes},year={1998},month={09},date={1998-09-08},url={http://mug.ee.auth.gr/wp-content/uploads/DOUL638.pdf},abstract={In this paper, we present an analysis filter design technique which optimally defines the proper decimator so that the quantization noise is compensated. The analysis is based on a distortion criterion minimization using the Lagrange multipliers. The optimal decimation filters are derived through a Ricatti solution which involves both the quantization and the interpolation filters. Experimental results are presented indicating the good performance of the proposed technique versus conventional subband filter banks in the presence of quantization noise.}}

### 1997

 (C) Anastasios Delopoulos and Maria Rangoussi "Cumulants of a Multidimensional Process Observed at Rationally Related Resolutions" International Workshop on Sampling Theory and Applications, Aveiro, Protugal, 1997 Jan [Abstract][BibTex]@inproceedings{Delopoulos1997Cumulants,author={Anastasios Delopoulos and Maria Rangoussi},title={Cumulants of a Multidimensional Process Observed at Rationally Related Resolutions},booktitle={International Workshop on Sampling Theory and Applications},address={Aveiro, Protugal},year={1997},month={01},date={1997-01-01}} (C) Anastasios Delopoulos and Maria Rangoussi "The Fractal Behaviour of Unvoiced Plosives: A Means for Classification" 5th European Conference on Speech Communication and Technology (EUROSPEECH'97), Rhodes, Greece, 1997 Jan [Abstract][BibTex]@inproceedings{Delopoulos1997Fractal,author={Anastasios Delopoulos and Maria Rangoussi},title={The Fractal Behaviour of Unvoiced Plosives: A Means for Classification},booktitle={5th European Conference on Speech Communication and Technology (EUROSPEECH'97)},address={Rhodes, Greece},year={1997},month={01},date={1997-01-01}} (C) Anastasios Delopoulos, Maria Rangoussi and Demetrios Kalogeras "Fractional Sampling Rate Conversion in the 3rd Order Cumulant domain and Applications" 1997 13th International Conference on Digital Signal Processing Proceedings, 1997. DSP 97, pp. 157-160, IEEE, Santorini, Greece, 1997 Jul [Abstract][BibTex][pdf]In a variety of problems a random process is observed at different resolutions while knowledge of the corresponding scale conversion ratio usually contains useful information related to problem-specific quantities. A method is proposed which exploits cumulant domain relations of such signals in order to yield fractional estimates of the unknown conversion ratio. The noise insensitivity and shift invariance property of the cumulants offers advantages to the proposed method over signal domain alternatives. These advantages are discussed in two classes of practical problems involving 1-D and 2-D scale converted signals.@inproceedings{Delopoulos1997Fractional,author={Anastasios Delopoulos and Maria Rangoussi and Demetrios Kalogeras},title={Fractional Sampling Rate Conversion in the 3rd Order Cumulant domain and Applications},booktitle={1997 13th International Conference on Digital Signal Processing Proceedings, 1997. DSP 97},pages={157-160},publisher={IEEE},address={Santorini, Greece},year={1997},month={07},date={1997-07-02},url={http://mug.ee.auth.gr/wp-content/uploads/publications/00628001.pdf},doi={http://10.1109/ICDSP.1997.628001},abstract={In a variety of problems a random process is observed at different resolutions while knowledge of the corresponding scale conversion ratio usually contains useful information related to problem-specific quantities. A method is proposed which exploits cumulant domain relations of such signals in order to yield fractional estimates of the unknown conversion ratio. The noise insensitivity and shift invariance property of the cumulants offers advantages to the proposed method over signal domain alternatives. These advantages are discussed in two classes of practical problems involving 1-D and 2-D scale converted signals.}}

### 1996

 (C) Vassilios Alexopoulos, Anastasios Delopoulos and Stefanos Kollias "Towards a Standardization for Medical Video Encoding and Archiving" 14th International EuroPacs Meeting, Heraklion, Crete, Greece, 1996 Jan [Abstract][BibTex]@inproceedings{Alexopoulos1996Towards,author={Vassilios Alexopoulos and Anastasios Delopoulos and Stefanos Kollias},title={Towards a Standardization for Medical Video Encoding and Archiving},booktitle={14th International EuroPacs Meeting},address={Heraklion, Crete, Greece},year={1996},month={01},date={1996-01-01}} (C) Anastasios Delopoulos, Dimitrios Kalogeras, Vassilios Alexopoulos and Stefanos Kollias "Real Time MPEG-1 Video Transmission over Local Area Networks" Multimedia Communications and Video Coding, pp. 47-55, Berlin, Germany, 1996 Oct [Abstract][BibTex][pdf]In this work is presented the architecture of an MPEG-1 stream transmission system appropriate for point-to-point transfer of live video and audio over TCP/IP local area networks. The hardware and software modules of the system are presented as well. Experimental results on the statistical behavior of the generated and transmitted MPEG-1 stream are quoted.@inproceedings{Delopoulos1996Real,author={Anastasios Delopoulos and Dimitrios Kalogeras and Vassilios Alexopoulos and Stefanos Kollias},title={Real Time MPEG-1 Video Transmission over Local Area Networks},booktitle={Multimedia Communications and Video Coding},pages={47-55},address={Berlin, Germany},year={1996},month={10},date={1996-10-07},url={http://dx.doi.org/10.1007/978-1-4613-0403-6_7},doi={http://10.1007/978-1-4613-0403-6_7},abstract={In this work is presented the architecture of an MPEG-1 stream transmission system appropriate for point-to-point transfer of live video and audio over TCP/IP local area networks. The hardware and software modules of the system are presented as well. Experimental results on the statistical behavior of the generated and transmitted MPEG-1 stream are quoted.}} (C) Anastasios Delopoulos, Maria Rangoussi and Janne Andersen "Recognition of voiced speech from the bispectrum" 8th European Signal Processing Conference, 1996. EUSIPCO 1996., IEEE, Trieste, Italy, 1996 Jan [Abstract][BibTex][pdf]Recognition of voiced speech phonemes is addressed in this paper using features extracted from the bispectrum of the speech signal. Voiced speech is modeled as a superposition of coupled harmonics, located at frequencies that are multiples of the pitch and modulated by the vocal tract. For this type of signal, nonzero bispectral values are shown to be guaranteed by the estimation procedure employed. The vocal tract frequency response is reconstructed from the bispectrum on a set of frequency points that are multiples of the pitch. An AR model is next fitted on this transfer function. The AR coefficients are used as the feature vector for the subsequent classification step. Any finite dimension vector classifier can be employed at this point. Experiments using the LVQ neural classifier give satisfactory classification scores on real speech data, extracted from the DARPA/TIMIT speech corpus.@inproceedings{Delopoulos1996Recognition,author={Anastasios Delopoulos and Maria Rangoussi and Janne Andersen},title={Recognition of voiced speech from the bispectrum},booktitle={8th European Signal Processing Conference, 1996. EUSIPCO 1996.},publisher={IEEE},address={Trieste, Italy},year={1996},month={01},date={1996-01-01},url={http://mug.ee.auth.gr/wp-content/uploads/sr_5.pdf},abstract={Recognition of voiced speech phonemes is addressed in this paper using features extracted from the bispectrum of the speech signal. Voiced speech is modeled as a superposition of coupled harmonics, located at frequencies that are multiples of the pitch and modulated by the vocal tract. For this type of signal, nonzero bispectral values are shown to be guaranteed by the estimation procedure employed. The vocal tract frequency response is reconstructed from the bispectrum on a set of frequency points that are multiples of the pitch. An AR model is next fitted on this transfer function. The AR coefficients are used as the feature vector for the subsequent classification step. Any finite dimension vector classifier can be employed at this point. Experiments using the LVQ neural classifier give satisfactory classification scores on real speech data, extracted from the DARPA/TIMIT speech corpus.}}

### 1995

 (J) Georgios B. Giannakis and Anastasios Delopoulos "Cumulant based autocorrelation estimates of non-Gaussian linear processes" Signal Processing, 47, (1), pp. 1-17, 1995 Nov [Abstract][BibTex][pdf]Autocorrelation of linear random processes can be expressed in terms of their cumulants. Theoretical insensitivity of the latter to additive Gaussian noise of unknown covariance, is exploited in this paper to develop (within a scale) autocorrelation estimators of linear non-Gaussian time series using cumulants of order higher than two. Windowed projections of third-order cumulants are shown to yield strongly consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. Asymptotic variance expressions of the proposed estimators are also presented. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.@article{Giannakis2000Cumulant,author={Georgios B. Giannakis and Anastasios Delopoulos},title={Cumulant based autocorrelation estimates of non-Gaussian linear processes},journal={Signal Processing},volume={47},number={1},pages={1-17},year={1995},month={11},date={1995-11-01},url={http://dx.doi.org/10.1016/0165-1684(95)00095-X},doi={http://10.1016/0165-1684(95)00095-X},abstract={Autocorrelation of linear random processes can be expressed in terms of their cumulants. Theoretical insensitivity of the latter to additive Gaussian noise of unknown covariance, is exploited in this paper to develop (within a scale) autocorrelation estimators of linear non-Gaussian time series using cumulants of order higher than two. Windowed projections of third-order cumulants are shown to yield strongly consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. Asymptotic variance expressions of the proposed estimators are also presented. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.}} (J) Andreas Tirakis, Anastasios Delopoulos and Stefanos Kollias "2-D Filter Bank Design for Optimal Reconstruction using Limited Subband Information" IEEE Transanctions on Image Processing, 4, (8), pp. 1160-1165, 1995 Aug [Abstract][BibTex][pdf]In this correspondence, we propose design techniques for analysis and synthesis filters of 2-D perfect reconstruction filter banks (PRFB\'s) that perform optimal reconstruction when a reduced number of subband signals is used. Based on the minimization of the squared error between the original signal and some low-resolution representation of it, the 2-D filters are optimally adjusted to the statistics of the input images so that most of the signal\'s energy is concentrated in the first few subband components. This property makes the optimal PRFB\'s efficient for image compression and pattern representations at lower resolutions for classification purposes. By extending recently introduced ideas from frequency domain principal component analysis to two dimensions, we present results for general 2-D discrete nonstationary and stationary second-order processes, showing that the optimal filters are nonseparable. Particular attention is paid to separable random fields, proving that only the first and last filters of the optimal PRFB are separable in this case. Simulation results that illustrate the theoretical achievements are presented.@article{Tirakis1995Filter,author={Andreas Tirakis and Anastasios Delopoulos and Stefanos Kollias},title={2-D Filter Bank Design for Optimal Reconstruction using Limited Subband Information},journal={IEEE Transanctions on Image Processing},volume={4},number={8},pages={1160-1165},year={1995},month={08},date={1995-08-01},url={http://dx.doi.org/10.1109/83.403423},doi={http://10.1109/83.403423},abstract={In this correspondence, we propose design techniques for analysis and synthesis filters of 2-D perfect reconstruction filter banks (PRFB\\'s) that perform optimal reconstruction when a reduced number of subband signals is used. Based on the minimization of the squared error between the original signal and some low-resolution representation of it, the 2-D filters are optimally adjusted to the statistics of the input images so that most of the signal\\'s energy is concentrated in the first few subband components. This property makes the optimal PRFB\\'s efficient for image compression and pattern representations at lower resolutions for classification purposes. By extending recently introduced ideas from frequency domain principal component analysis to two dimensions, we present results for general 2-D discrete nonstationary and stationary second-order processes, showing that the optimal filters are nonseparable. Particular attention is paid to separable random fields, proving that only the first and last filters of the optimal PRFB are separable in this case. Simulation results that illustrate the theoretical achievements are presented.}}

### 1995

 (C) Maria Rangoussi and Anastasios Delopoulos "Classification of Consonants using Wigner Distribution Features" 12th International Conference on DSP, Limassol, Cyprus, 1995 Jan [Abstract][BibTex]@inproceedings{Rangoussi1995Classification,author={Maria Rangoussi and Anastasios Delopoulos},title={Classification of Consonants using Wigner Distribution Features},booktitle={12th International Conference on DSP},address={Limassol, Cyprus},year={1995},month={01},date={1995-01-01}} (C) Maria Rangoussi and Anastasios Delopoulos "Recognition of Unvoiced Stops from their Time-Frequency Representation" 1995 International Conference on Acoustics, Speech, and Signal Processing, 1995. ICASSP-95., pp. 792-795, IEEE, Detroit, MI, 1995 May [Abstract][BibTex][pdf]The recognition of the unvoiced stop sounds /k/, /p/ and /t/ in a speech signal is an interesting problem, due to the irregular, aperiodic, nonstationary nature of the corresponding signals. Their spotting is much easier, however, thanks to the characteristic silence interval they include. Classification of these three phonemes is proposed, based on the patterns extracted from their time-frequency representation. This is possible because the different articulation points of /k/, /p/ and /t/ are reflected into distinct patterns of evolution of their spectral contents with time. These patterns can be obtained by suitable time-frequency analysis, and then used for classification. The Wigner distribution of the unvoiced stop signals, appropriately smoothed and subsampled, is proposed as the basic classification pattern. Finally, for the classification step, the learning vector quantization (LVQ) classifier of Kohonen (1988) is employed on a set of unvoiced stop signals extracted from the TIMIT speech database, with encouraging results under context- and speaker-independent testing conditions.@inproceedings{Rangoussi1995Recognition,author={Maria Rangoussi and Anastasios Delopoulos},title={Recognition of Unvoiced Stops from their Time-Frequency Representation},booktitle={1995 International Conference on Acoustics, Speech, and Signal Processing, 1995. ICASSP-95.},pages={792-795},publisher={IEEE},address={Detroit, MI},year={1995},month={05},date={1995-05-09},url={http://dx.doi.org/10.1109/ICASSP.1995.479813},doi={http://10.1109/ICASSP.1995.479813},abstract={The recognition of the unvoiced stop sounds /k/, /p/ and /t/ in a speech signal is an interesting problem, due to the irregular, aperiodic, nonstationary nature of the corresponding signals. Their spotting is much easier, however, thanks to the characteristic silence interval they include. Classification of these three phonemes is proposed, based on the patterns extracted from their time-frequency representation. This is possible because the different articulation points of /k/, /p/ and /t/ are reflected into distinct patterns of evolution of their spectral contents with time. These patterns can be obtained by suitable time-frequency analysis, and then used for classification. The Wigner distribution of the unvoiced stop signals, appropriately smoothed and subsampled, is proposed as the basic classification pattern. Finally, for the classification step, the learning vector quantization (LVQ) classifier of Kohonen (1988) is employed on a set of unvoiced stop signals extracted from the TIMIT speech database, with encouraging results under context- and speaker-independent testing conditions.}}

### 1994

 (J) Anastasios Delopoulos and Georgios B. Giannakis "Consistent identification of stochastic linear systems with noisy input-output data" Automatica, 30, (8), pp. 1271-1294, 1994 Aug [Abstract][BibTex][pdf]A novel criterion is introduced for parametric errors-in-variables identification of stochastic linear systems excited by non-Gaussian inputs. The new criterion is (at least theoretically) insensitive to a class of input-output disturbances because it implicitly involves higher- than second-order cumulant statistics. In addition, it is shown to be equivalent to the conventional Mean-Squared Error (MSE) as if the latter was computed in the ideal case of noise-free input-output data. The sampled version of the criterion converges to the novel MSE and guarantees strongly consistent parameter estimators. The asymptotic behavior of the resulting parameter estimators is analyzed and guidelines for minimum variance experiments are discussed briefly. Informative enough input signals and persistent of excitation conditions are specified. Computatonally attractive Recursive-Least-Squares variants are also developed for on-line implementation of ARMA modeling, and their potential is illustrated by applying them to time-delay estimation in low SNR environment. The performance of the proposed algorithms and comparisons with conventional methods are corroborated using simulated data.@article{Delopoulos1994Consistent,author={Anastasios Delopoulos and Georgios B. Giannakis},title={Consistent identification of stochastic linear systems with noisy input-output data},journal={Automatica},volume={30},number={8},pages={1271-1294},year={1994},month={08},date={1994-08-01},url={http://mug.ee.auth.gr/wp-content/uploads/1-s2.0-0005109894901082-main.pdf},doi={http://10.1016/0005-1098(94)90108-2},abstract={A novel criterion is introduced for parametric errors-in-variables identification of stochastic linear systems excited by non-Gaussian inputs. The new criterion is (at least theoretically) insensitive to a class of input-output disturbances because it implicitly involves higher- than second-order cumulant statistics. In addition, it is shown to be equivalent to the conventional Mean-Squared Error (MSE) as if the latter was computed in the ideal case of noise-free input-output data. The sampled version of the criterion converges to the novel MSE and guarantees strongly consistent parameter estimators. The asymptotic behavior of the resulting parameter estimators is analyzed and guidelines for minimum variance experiments are discussed briefly. Informative enough input signals and persistent of excitation conditions are specified. Computatonally attractive Recursive-Least-Squares variants are also developed for on-line implementation of ARMA modeling, and their potential is illustrated by applying them to time-delay estimation in low SNR environment. The performance of the proposed algorithms and comparisons with conventional methods are corroborated using simulated data.}} (J) Anastasios Delopoulos, A. Tirakis and Stephanos Kollias "Invariant image classification using triple-correlation-based neural networks" IEEE Transactions on Neural Networks, 5, (3), pp. 392-408, 1994 May [Abstract][BibTex][pdf]Triple-correlation-based neural networks are introduced and used in this paper for invariant classification of 2D gray scale images. Third-order correlations of an image are appropriately clustered, in spatial or spectral domain, to generate an equivalent image representation that is invariant with respect to translation, rotation, and dilation. An efficient implementation scheme is also proposed, which is robust to distortions, insensitive to additive noise, and classifies the original image using adequate neural network architectures applied directly to 2D image representations. Third-order neural networks are shown to be a specific category of triple-correlation-based networks, applied either to binary or gray-scale images. A simulation study is given, which illustrates the theoretical developments, using synthetic and real image data.@article{Delopoulos1994Invariant,author={Anastasios Delopoulos and A. Tirakis and Stephanos Kollias},title={Invariant image classification using triple-correlation-based neural networks},journal={IEEE Transactions on Neural Networks},volume={5},number={3},pages={392-408},year={1994},month={05},date={1994-05-01},url={http://dx.doi.org/10.1109/72.286911},doi={http://10.1109/72.286911},abstract={Triple-correlation-based neural networks are introduced and used in this paper for invariant classification of 2D gray scale images. Third-order correlations of an image are appropriately clustered, in spatial or spectral domain, to generate an equivalent image representation that is invariant with respect to translation, rotation, and dilation. An efficient implementation scheme is also proposed, which is robust to distortions, insensitive to additive noise, and classifies the original image using adequate neural network architectures applied directly to 2D image representations. Third-order neural networks are shown to be a specific category of triple-correlation-based networks, applied either to binary or gray-scale images. A simulation study is given, which illustrates the theoretical developments, using synthetic and real image data.}}

### 1994

 (C) Anastasios Delopoulos and Stefanos Kollias "Optimal filterbanks for signal reconstruction from noisy subband components" 28th ASILOMAR Conference on Signals, Systems and Computers, Asilomar CA, USA, 1994 Jan [Abstract][BibTex]@inproceedings{Delopoulos1994Optimal,author={Anastasios Delopoulos and Stefanos Kollias},title={Optimal filterbanks for signal reconstruction from noisy subband components},booktitle={28th ASILOMAR Conference on Signals, Systems and Computers},address={Asilomar CA, USA},year={1994},month={01},date={1994-01-01}} (C) Nikolaos G. Panagiotidis, Anastasios Delopoulos and Stefanos D. Kollias "Neural-Network Based Classification of Laser-Doppler Flowmetry Signals" 1994 IEEE Workshop on Neural Networks for Signal Processing, pp. 709-718, Ermioni, 1994 Sep [Abstract][BibTex][pdf]Laser Doppler flowmetry is the most advantageous technique for non-invasive patient monitoring. Based on the Doppler principle, signals corresponding to blood flow are generated, and metrics corresponding to healthy vs. patient samples are extracted. A neural-network based classifier for these metrics is proposed. The signals are initially filtered and transformed into the frequency domain through third-order correlation and bispectrum estimation. The pictorial representation of the correlations is subsequently routed into a neural network based multilayer perceptron classifier, which is described in detail. Finally, experimental results demonstrating the efficiency of the proposed scheme are presented.@inproceedings{Panagiotidis1994Neural,author={Nikolaos G. Panagiotidis and Anastasios Delopoulos and Stefanos D. Kollias},title={Neural-Network Based Classification of Laser-Doppler Flowmetry Signals},booktitle={1994 IEEE Workshop on Neural Networks for Signal Processing},pages={709-718},address={Ermioni},year={1994},month={09},date={1994-09-06},url={http://mug.ee.auth.gr/wp-content/uploads/publications/00365994.pdf},doi={http://10.1109/NNSP.1994.365994},abstract={Laser Doppler flowmetry is the most advantageous technique for non-invasive patient monitoring. Based on the Doppler principle, signals corresponding to blood flow are generated, and metrics corresponding to healthy vs. patient samples are extracted. A neural-network based classifier for these metrics is proposed. The signals are initially filtered and transformed into the frequency domain through third-order correlation and bispectrum estimation. The pictorial representation of the correlations is subsequently routed into a neural network based multilayer perceptron classifier, which is described in detail. Finally, experimental results demonstrating the efficiency of the proposed scheme are presented.}} (C) Andreas Tirakis, Anastasios Delopoulos and Stefanos Kollias "Invariant Image Recognition Using Triple Correlations and Neural Networks" IEEE International Conference on Neural Networks, pp. 4055-4060, Orlando FL, USA, 1994 Jun [Abstract][BibTex]Triple-correlation-based image representations were previously (Delopoulos, Tirakis, and Kollias, 1994) combined with neural network architectures for deriving an invariant, with respect to translation, rotation and dilation, robust classification scheme. Efficient implementations are described in this paper, which reduce the computational complexity of the method. Hierarchical, multiresolution neural networks are proposed as an effective architecture for achieving this purpose.@inproceedings{Tirakis1994Invariant,author={Andreas Tirakis and Anastasios Delopoulos and Stefanos Kollias},title={Invariant Image Recognition Using Triple Correlations and Neural Networks},booktitle={IEEE International Conference on Neural Networks},pages={4055-4060},address={Orlando FL, USA},year={1994},month={06},date={1994-06-27},abstract={Triple-correlation-based image representations were previously (Delopoulos, Tirakis, and Kollias, 1994) combined with neural network architectures for deriving an invariant, with respect to translation, rotation and dilation, robust classification scheme. Efficient implementations are described in this paper, which reduce the computational complexity of the method. Hierarchical, multiresolution neural networks are proposed as an effective architecture for achieving this purpose.}}

### 1992

 (J) Anastasios Delopoulos and Georgios B. Giannakis "Strongly consistent identification algorithms and noise insensitive MSE criteria" IEEE Transactions on Signal Processing, 40, (8), pp. 1955-1970, 1992 Aug [Abstract][BibTex][pdf]Windowed cumulant projections of nonGaussian linear processes yield autocorrelation estimators which are immune to additive Gaussian noise of unknown covariance. By establishing strong consistency of these estimators, strongly consistent and noise insensitive recursive algorithms are developed for parameter estimation. These computationally attractive schemes are shown to be optimal with respect to a modified mean-square-error (MSE) criterion which implicitly exploits the high signal-to-noise ratio domain of cumulant statistics. The novel MSE objective function is expressed in terms of the noisy process, but it is shown to be a scalar multiple of the standard MSE criterion as if the latter was computed in the absence of noise. Simulations illustrate the performance of the proposed algorithms and compare them with the conventional algorithms.@article{Delopoulos1992Strongly,author={Anastasios Delopoulos and Georgios B. Giannakis},title={Strongly consistent identification algorithms and noise insensitive MSE criteria},journal={IEEE Transactions on Signal Processing},volume={40},number={8},pages={1955-1970},year={1992},month={08},date={1992-08-01},url={http://dx.doi.org/10.1109/78.149997},doi={http://10.1109/78.149997},abstract={Windowed cumulant projections of nonGaussian linear processes yield autocorrelation estimators which are immune to additive Gaussian noise of unknown covariance. By establishing strong consistency of these estimators, strongly consistent and noise insensitive recursive algorithms are developed for parameter estimation. These computationally attractive schemes are shown to be optimal with respect to a modified mean-square-error (MSE) criterion which implicitly exploits the high signal-to-noise ratio domain of cumulant statistics. The novel MSE objective function is expressed in terms of the noisy process, but it is shown to be a scalar multiple of the standard MSE criterion as if the latter was computed in the absence of noise. Simulations illustrate the performance of the proposed algorithms and compare them with the conventional algorithms.}}

### 1992

 (C) Anastasios Delopoulos, Andreas Tirakis and Stefanos Kollias "Invariant image recognition using triple correlations" Proc. of EUSIPCO-92, Brussels, Belgium, 1992 Jan [Abstract][BibTex]@inproceedings{Delopoulos1992Invariant,author={Anastasios Delopoulos and Andreas Tirakis and Stefanos Kollias},title={Invariant image recognition using triple correlations},booktitle={Proc. of EUSIPCO-92},address={Brussels, Belgium},year={1992},month={01},date={1992-01-01}} (C) Andreas Tirakis, Anastasios Delopoulos and Stefanos Kollias "Cumulant-based neural network classifiers" Proc. of International Conference on Artificial Neural Networks ICANN92, Brighton, UK, 1992 Jan [Abstract][BibTex]@inproceedings{Tirakis1992Cumulant,author={Andreas Tirakis and Anastasios Delopoulos and Stefanos Kollias},title={Cumulant-based neural network classifiers},booktitle={Proc. of International Conference on Artificial Neural Networks ICANN92},address={Brighton, UK},year={1992},month={01},date={1992-01-01}}

### 1991

 (C) Anastasios Delopoulos and Georgios B. Giannakis "Input Design for Consistent Identification in the Presence of Input/Output Noise" Proc. of Intl. Signal Processing Workshop on Higher-Order Statistics, Chamrousse, France, 1991 Jan [Abstract][BibTex]@inproceedings{Delopoulos1991Input,author={Anastasios Delopoulos and Georgios B. Giannakis},title={Input Design for Consistent Identification in the Presence of Input/Output Noise},booktitle={Proc. of Intl. Signal Processing Workshop on Higher-Order Statistics},address={Chamrousse, France},year={1991},month={01},date={1991-01-01}} (C) Anastasios Delopoulos and Georgios B. Giannakis "Strongly consistent output only and input-ouput identification in the presence of Gaussian noise" Proc. of Intl. Conf. on ASSP,(ICASSP '91), Toronto, Canada, 1991 Jan [Abstract][BibTex]@inproceedings{Delopoulos1991Strongly,author={Anastasios Delopoulos and Georgios B. Giannakis},title={Strongly consistent output only and input-ouput identification in the presence of Gaussian noise},booktitle={Proc. of Intl. Conf. on ASSP,(ICASSP '91)},address={Toronto, Canada},year={1991},month={01},date={1991-01-01}}

### 1990

 (J) Georgios Giannakis and Anastasios Delopoulos "Nonparametric estimation of autocorrelation and spectra using cumulants and polyspectra" Advanced Signal Processing Algorithms, Architectures, and Implementations, 503, 1990 Nov [Abstract][BibTex][pdf]Autocorrelation and specira of linear random processes can be expressed in terms of cumulants and polyspectra respectively. The insensitivity of the latter to additive Gaussian noise of unknown covariance is exploited in this paper to develop spectral estimators of deterministic and linear non-Gaussian signals using polyspectra. In the time-domain windowed projections of third-order cumulants are shown to yield consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. In the frequency-domain a Fourier-slice solution and a least-squares approach are described for performing spectral analysis through windowed bi-periodograms. Asymptotic variance expressions of the time- and frequencydomain estimators are also presented. Two-dimensional extensions are indicated and potential applications are discussed. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.@article{Giannakis1990Nonparametric,author={Georgios Giannakis and Anastasios Delopoulos},title={Nonparametric estimation of autocorrelation and spectra using cumulants and polyspectra},journal={Advanced Signal Processing Algorithms, Architectures, and Implementations},volume={503},year={1990},month={11},date={1990-11-01},url={http://dx.doi.org/10.1117/12.23504},doi={http://10.1117/12.23504},abstract={Autocorrelation and specira of linear random processes can be expressed in terms of cumulants and polyspectra respectively. The insensitivity of the latter to additive Gaussian noise of unknown covariance is exploited in this paper to develop spectral estimators of deterministic and linear non-Gaussian signals using polyspectra. In the time-domain windowed projections of third-order cumulants are shown to yield consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. In the frequency-domain a Fourier-slice solution and a least-squares approach are described for performing spectral analysis through windowed bi-periodograms. Asymptotic variance expressions of the time- and frequencydomain estimators are also presented. Two-dimensional extensions are indicated and potential applications are discussed. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.}}

### 1990

 (C) Anastasios Delopoulos and Georgios B. Giannakis "Strongly consistent identification algorithms and noise insensitive MSE criteria" Proc. of 4th Digital Signal Processing Workshop, New Paltz NY, USA, 1990 Jan [Abstract][BibTex]@inproceedings{Delopoulos1990Strongly,author={Anastasios Delopoulos and Georgios B. Giannakis},title={Strongly consistent identification algorithms and noise insensitive MSE criteria},booktitle={Proc. of 4th Digital Signal Processing Workshop},address={New Paltz NY, USA},year={1990},month={01},date={1990-01-01}} (C) Georgios Giannakis and Anastasios Delopoulos "Nonparametric estimation of autocorrelation and spectra using cumulants and polyspectra" Proc. of Soc. of Photo-Opt. Instr. Eng., Advanced Signal Processing Alg., and Implem.(SPIE '90), 1990 Nov [Abstract][BibTex][pdf]Autocorrelation and specira of linear random processes can be expressed in terms of cumulants and polyspectra respectively. The insensitivity of the latter to additive Gaussian noise of unknown covariance is exploited in this paper to develop spectral estimators of deterministic and linear non-Gaussian signals using polyspectra. In the time-domain windowed projections of third-order cumulants are shown to yield consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. In the frequency-domain a Fourier-slice solution and a least-squares approach are described for performing spectral analysis through windowed bi-periodograms. Asymptotic variance expressions of the time- and frequencydomain estimators are also presented. Two-dimensional extensions are indicated and potential applications are discussed. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.@inproceedings{Giannakis1990,author={Georgios Giannakis and Anastasios Delopoulos},title={Nonparametric estimation of autocorrelation and spectra using cumulants and polyspectra},booktitle={Proc. of Soc. of Photo-Opt. Instr. Eng., Advanced Signal Processing Alg., and Implem.(SPIE '90)},year={1990},month={11},date={1990-11-01},url={http://dx.doi.org/10.1117/12.23504},doi={http://10.1117/12.23504},abstract={Autocorrelation and specira of linear random processes can be expressed in terms of cumulants and polyspectra respectively. The insensitivity of the latter to additive Gaussian noise of unknown covariance is exploited in this paper to develop spectral estimators of deterministic and linear non-Gaussian signals using polyspectra. In the time-domain windowed projections of third-order cumulants are shown to yield consistent estimators of the autocorrelation sequence. Both batch and recursive algorithms are derived. In the frequency-domain a Fourier-slice solution and a least-squares approach are described for performing spectral analysis through windowed bi-periodograms. Asymptotic variance expressions of the time- and frequencydomain estimators are also presented. Two-dimensional extensions are indicated and potential applications are discussed. Simulations are provided to illustrate the performance of the proposed algorithms and compare them with conventional approaches.}}