D. Tzovaras

Bio: D. Tzovaras is an academic researcher. The author has contributed to research in topics: Bayes' theorem & Adaptive filter. The author has an hindex of 2, co-authored 5 publications receiving 11 citations.

Blockiness detection in compressed data

Abstract: A novel frequency domain technique for image blocking artifact detection is presented. The algorithm detects the regions of the image which present visible blocking artifacts. This detection is performed in the frequency domain and uses the estimated relative quantization error calculated when the DCT coefficients are modeled by a Laplacian probability function. Experimental results illustrating the performance of the proposed method are presented and evaluated.

Detection of occlusion and visible background and foreground areas in stereo image pairs

Abstract: An efficient technique based on the Bayes test is introduced in this paper for the identification of the occlusion and visible background and foreground areas in a noisy stereoscopic image pair. Four hypotheses are used for the formulation of a compound Bayes decision rules. Experimental results illustrating the performance of the proposed techniques are presented and evaluated.

A compound Bayes test for detection of occlusion and visible background and foreground areas in stereo

Abstract: An efficient technique based on the Bayes test is introduced in this paper, for the identification of the occlusion and visible background and foreground areas in a noisy stereoscopic image pair. Four hypotheses are used for the formulation of compound Bayes decision rules. Experimental results illustrating the performance of the proposed techniques are presented and evaluated.

Occlusion detection in stereopairs

Abstract: An efficient technique based on the Bayes test is introduced, for detecting occlusions in a noisy stereoscopic image pair. Two hypotheses are used for the formulation of the Bayes decision rules: the first describes the displaced areas while the other describes the occlusion areas. Experimental results illustrating the performance of the proposed techniques are presented and evaluated.

Technical section An efficient algorithm for the enhancement of JPEG-coded images $

Abstract: Despite its growing age, the JPEG is among the most popular choices as a standard compression scheme for continuous-tone still images. In this paper, a novel technique is proposed to alleviate the blocking artifacts that usually occur in JPEG coded images especially at low bit rates. The proposed algorithm consists of two stages: firstly, the AC coefficients are estimated based on their observed probability distribution and secondly, a postprocessingscheme is applied for blockiness removal, consisting of a region classification algorithm and a spatial adaptive filtering. Experimental results demonstrate the efficiency of the proposed method. r 2003 Elsevier Ltd. All rights reserved.

Efficient disparity vector coding for multiview sequences

Abstract: A multiview sequence codec with view scalability was described in a previous paper. To enhance the performance of this codec, an efficient disparity vector coding method for multiview sequences is proposed herein. For higher coding efficiency, we encode the differential vectors acquired by subtracting the original vectors from the predicted ones. To enhance the performance of disparity vector coding, it is essential to predict the disparity vectors accurately. The prediction by this proposed method utilizes the correlation among the multiview images, while conventional methods exploit the correlation among the causal blocks. Experiments were performed for three different 5 view sequences. We were able to confirm that the proposed method predicts disparity vectors accurately by comparing the entropy and the mean absolute values for differential vectors with conventional methods. Its performance is superior to vector coding methods used in MPEG-4 which uses only a spatial correlation. The proposed method increases the coding efficiency by a factor of 30–45% while preserving image quality.

Blocking artifact reduction in frequency domain

Abstract: A novel frequency domain technique for image blocking artifact reduction is presented. For each block, its DC and AC coefficients are recalculated for artifact reduction. To achieve this, a closed form representation of the optimal correction of the DCT coefficients is produced by minimizing a novel enhanced form of the mean squared difference of slope (MSDS), for every frequency separately. This correction of each DCT coefficient depends on the eight neighboring coefficients in the subband-like representation of the DCT and is constrained by the upper and lower bound of the quantized DCT coefficients. Experimental results illustrating the performance of the proposed method are presented and evaluated.

A Bayesian segmentation of stereo pairs

Abstract: A Bayesian scheme is proposed for the identification of the occlusion and visible background and foreground areas in a noisy stereoscopic image pair. Three hypotheses are used for the formulation of Bayes decision rules: the first describes the visible foreground areas, the second describes the visible background areas and the last describes the occlusion areas. Experimental results illustrating the performance of the proposed technique are presented and evaluated.

Mean time between visible artifacts in visual communications

Abstract: To my parents and my sister i ACKNOWLEDGEMENTS I thank my advisor, Dr. Nikil Jayant for teaching me how to be successful in the technological world, and for having complete faith in me right from the start to the finish of my PhD, and beyond. I would like to take the opportunity to thank my committee members, Dr. Constantine Dovrolis for being an integral part of my doctoral degree. I wish to thank Dr. Jayant again, for being an expert at choosing his co-workers. I am grateful to Barbara for setting an excellent example by being highly efficient and organized, and for being the gregarious person that helped me in my subjective experiments and scheduling issues. I am also thankful to Rex for helping in just about every technical aspect of my projects. I would like to thank Tina for organizing all the monetary issues related to my studies and company work. I had quite a bit of travel during my studies, and I am thankful to JoAnna for making sure that my trips were smooth. I would like to thank Pravin for being a keystone player in the development of the technology in the company that our team started up. I am grateful to Roberto and the other people from Venture lab for having faith in our capabilities. I would like to thank all my friends in the GCATT building-Arumugam, Babak, Jeannie, Nicolas, Rafi and Souvik, for being excellent peers. I would like to make a special mention of Parashuram and Yogesh, who have stuck with me since long before coming to Georgia Tech, enough to have made a significant impact on my personal and professional life. Last, but definitely not the least, I thank my family-my parents and my sister for always having believed in me and providing a constant source of encouragement. They made all this effort worth it.

Detection of blocking artifact on satellite image and its new evaluator

Abstract: New algorithms for blocking artifact detection on a compressed satellite image by using a 7×7 block and for analyzing its characteristics are proposed. Blocking artifacts often appear on an image when it has a very high compression rate based on either the loss-compression or lossless compression. Localization of blocking artifact is useful for finding the image's characteristics. This study also proposes methods of image quality metric that will analyze the characteristic of distorted satellite image caused by blocking artifact based on the rate-distortion and the similarity. In addition, we propose a new evaluator, which combines precision and recall, as a more suitable measure than MSE for error measurement in imbalanced data. Experimental evaluations show that our proposal works well for satellite images.