George A. Triantafyllidis

Blocking artifact detection and reduction in compressed data

A novel frequency-domain technique for image blocking artifact detection and reduction is presented. The algorithm first 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 discrete cosine transform (DCT) coefficients are modeled by a Laplacian probability function. Then, for each block affected by blocking artifacts, 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 for every frequency separately. This correction of each DCT coefficient depends on the eight neighboring coefficients in the subband-like representation of the DCT transform and is constrained by the quantization upper and lower bound. Experimental results illustrating the performance of the proposed method are presented and evaluated.

Detection of blocking artifacts of compressed still images

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.

A context based adaptive arithmetic coding technique for lossless image compression

Significant progress has recently been made in lossless image compression using discrete wavelet transforms. The overall performance of these schemes may be further improved by properly designing efficient entropy coders. A new technique is introduced for the implementation of context based adaptive arithmetic entropy coding. This technique is based on the prediction of the value of the current transform coefficient, using a weighted least squares method, in order to achieve appropriate context selection for arithmetic coding. Experimental results illustrate and evaluate the performance of the proposed technique.

Mobile tele-echography: user interface design

Ultrasound imaging allows the evaluation of the degree of emergency of a patient. However, in some instances, a well-trained sonographer is unavailable to perform such echography. To cope with this issue, the Mobile Tele-Echography Using an Ultralight Robot (OTELO) project aims to develop a fully integrated end-to-end mobile tele-echography system using an ultralight remote-controlled robot for population groups that are not served locally by medical experts. This paper focuses on the user interface of the OTELO system, consisting of the following parts: an ultrasound video transmission system providing real-time images of the scanned area, an audio/video conference to communicate with the paramedical assistant and with the patient, and a virtual-reality environment, providing visual and haptic feedback to the expert, while capturing the experts hand movements. These movements are reproduced by the robot at the patient site while holding the ultrasound probe against the patient skin. In addition, the user interface includes an image processing facility for enhancing the received images and the possibility to include them into a database.

Occlusion and visible background and foreground areas in stereo: a Bayesian approach

Efficient techniques are introduced in this paper for the identification of the occlusion and visible background and foreground areas in a noisy stereoscopic image pair. Three different Bayes decision methods are tested for this purpose. The first, and uses three hypotheses for the formulation of the Bayes decision rules, adopting the right image as a reference. After performing a dual-Bayes decision test having each time as a different image of the stereo pair as reference, consistency checking is added to these tests to form the second method. Finally, four compound hypotheses are used in the third method, which is the most accurate but also the more detailed and computationally involved of three. Experimental results illustrating the performance of the techniques are presented and evaluated.

Blocking artifact reduction in frequency domain

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.

Combined frequency and spatial domain algorithm for the removal of blocking artifacts

A novel combined frequency and spatial domain method is presented in this paper for blockiness reduction for low bit rate compressed images. The method consists of two stages: in the first, better estimates of the reconstructed DCT coefficients are obtained based on their observed probability distribution. In the second, an efficient postprocessing scheme consisting of a region classification algorithm and a spatial adaptive filtering is applied for blockiness removal. The type of filtering is decided on the basis of an estimation of the local characteristics of the coded image. The main advantage of the proposed method is the efficient combination and design of these two stages which are acting complementarily for the reduction of blocking artifacts. This approach is shown to produce excellent results in removing blocking artifacts. The efficient performance of the proposed algorithm is due, firstly, to the proposition that the shape and the position of the filter kernel are adjusted according to the characteristics of the local image region and secondly, to the employment of the modified improved DCT coefficients by the postprocessing filter. Experimental results illustrating the performance of the proposed method are presented and evaluated.

Rigid and Non-Rigid 3D Motion Estimation from Multiview Image Sequences

Multiview image sequence processing has been the focus of considerable attention in recent literature. This paper presents an efficient technique for object-based rigid and non-rigid 3D motion estimation, applicable to problems occurring in multiview image sequence coding applications. More specifically, a neural network is formed for the estimation of the rigid 3D motion of each object in the scene, using initially estimated 2D motion vectors corresponding to each camera view. Non-linear error minimization techniques are adopted for neural network weight update. Furthermore, a novel technique is also proposed for the estimation of the local non-rigid deformations, based on the multiview camera geometry. Experimental results using both stereoscopic and trinocular camera setups illustrate and evaluate the proposed scheme.

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 postprocessing scheme 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.

Blockiness detection in compressed data

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.