Antonio Chimienti

Frame concealment for H.264/AVC decoders

The H.264/AVC offers a high video coding efficiency and is the first standard that provides an explicit support for the transmission of multimedia content over a packed switched network, specifying a network abstraction layer (NAL). If we consider the transmission of a low resolution video sequence over a wireless LAN network or a UMTS link, we can usually observe that a coded picture typically fits the packet size, therefore a transmission error produces the loss of a whole frame. In this paper, we propose a novel technique to perform the concealment of a whole frame for H.264/A VC video decoders.

Statistical analysis of the 2D-DCT coefficients of the differential signal for images

Abstract Block-matching motion compensation techniques are widely used in image coding algorithms. A differential signal with different characteristics from the original signal is then generated. It is important to know the statistical properties of the signal source in order to correctly characterize some parameters of the digital image coding scheme. In this paper a statistical study of the 2D-DCT coefficients of the motion-compensated blocks is performed. The results of this study indicate that the statistics of the coefficients are best approximated by a Laplacian pdf (probability density function). The influence of some types of normalization is investigated and the corresponding pdfs are estimated. An analysis indicates that the Laplacian pdf may be used as a good approximation for the statistical properties of the normalized coefficients.

A complexity-bounded motion estimation algorithm

The full search motion estimation algorithm for video coding is a procedure of high computational cost. For this reason, in real-time low-power applications, low-cost motion estimation algorithms are viable solutions. A novel reduced complexity motion estimation algorithm is presented. It conjugates the reduction of computational load with good encoding efficiency. It exploits the past history of the motion field to predict the current motion field. A successive refinement phase gives the final motion field. This approach leads to a sensible reduction in the number of motion vector that have to be tested. The complexity is lower than any other algorithm algorithms known to the authors, in the literature, it is constant as there is no recursivity in the algorithm and independent of any search window area size. Experimental evaluations have shown the robustness of the algorithm when applied on a wide set of video sequences--a good performance compared to other reduced complexity algorithms and negligible loss of efficiency versus the full search algorithm.

A Novel Adaptive Vector Quantization Method For Memory Reduction In Mpeg-2 Hdtv Decoders

A novel method to reduce the external memory needed by an MPEG-2 HDTV decoder architecture is presented and discussed. The total amount of memory is reduced from 96 to 32 Mbits preserving a good picture quality. Furthermore the approach chosen maintains a low hardware complexity and increases less than 5%, in 0.35 /spl mu/m technology, the total decoder silicon area with respect to the standard decoder.

Robust Low-Delay Video Transmission using H.264/AVC Redundant Slices and Flexible Macroblock Ordering

This paper proposes a scheme for low-delay robust transmission of video signals over packet erasure channels. In applications such as video conferencing, the permissible delay between encoding and playback may be too low to allow retransmission or channel coding approaches which require buffering several video packets. For such a scenario, we present a scheme that provides error robustness using redundant video descriptions applied to pertinent portions of the video signal. In the H.264/AVC specification, this can be efficiently implemented using redundant slices and flexible macroblock ordering (FMO). We describe a model that determines the bit rate of the redundant descriptions such that the expected distortion at the decoder is minimized. Across all the video test sequences used, the average video quality delivered by the proposed scheme is 3.7 dB higher than decoder-based error concealment, and 1.2 dB higher than encoder-based loss-aware rate-distortion optimization.

Motion compensation and multiresolution coding

Abstract Multiresolution techniques have become more and more appealing in current image coding. Image multispectral representation produces many important features such as spectral shaping of coding noise according to human eye perception, good image energy compaction, coder tuning with respect to any band characteristics, and allows for multilevel layered transmission that is one of the main targets pursued by the broadcaster. Despite these appealing capabilities, multiresolution techniques have failed to give the expected results. One of the reasons for this failure is the difficulty of exploiting the temporal redudancy present in image sequences. This paper addresses the problem of motion compensation in a multiresolution environment, considering both QMF-SBC and wavelet transform approaches. Different motion compensation schemes are derived and their efficiency is considered with regard to scalability and to the lengths of subband analysis and synthesis filters. Simulation results are used to support relevant conclusions where needed.

A low complexity concealment algorithm for the whole-frame loss in H.264/AVC

The H.264/AVC video coding standard [Joint Video Team, 2003] offers a high coding efficiency and is the first standard that provides an explicit support for the transmission of multimedia content over a packet switched network, specifying a network abstraction layer (NAL). If we consider the transmission of a low resolution video sequence over a wireless LAN network, we can usually observe that a coded frame typically fits the packet size, therefore a transmission error usually produces the loss of a NAL unit and hence of a whole frame. In this paper we propose a low complexity algorithm useful for the concealment of a whole frame, based upon the optical flow concept.

Improving calibration accuracy of structured light systems using plane-based residual error compensation

Abstract. The performance of a structured light system (SLS) highly depends on its calibration especially in applications such as surface metrology and product quality control where high accuracy is required. Motivated by building a real-time highly accurate flatness measurement system, we propose a plane-based residual error compensation algorithm for improving the calibration accuracy of SLSs. Following the highly accurate procedure of geometric calibration using circular control points, the proposed algorithm enforces the planar constraint on the three-dimensional reconstruction of the circular control points, which are projected on a perfect plane, to further reduce the residual calibration error. Our method compensates for the largest proportion of the residual error, in most cases being the model error of the lens distortion in the system. Experimental results show that the compensation elevates the calibration accuracy to a higher level—the planarity error is reduced by 70% and this accuracy is comparable to a well-reputed industrial mechanical measuring machine.

Enhancing whole-frame error concealment with an intra motion vector estimator in H.264/AVC

The novel H.264/AVC video coding specification provides a significant improvement in terms of coding efficiency compared to previous standards. In certain streaming scenarios, the problem of whole-frame loss concealment can arise when using H.264/AVC. Two different algorithms have been proposed to conceal a lost image, based on the optical flow concept. In a real streaming scenario, an encoder usually introduces some kind of intra refresh policy that can insert trouble concealment algorithms leaving gaps in the motion vector field used for reference. We discuss the advantages of introducing a motion vector estimator for such intra coded regions.

Combining DCT and subband coding into an intraframe coder

Abstract The advent of broadband digital networks will make it possible to transmit high quality digital television. Subband coding is a very interesting coding scheme as it accommodates a transmission quality that can flexibly adapt to the available channel capacity. Subband coding (SBC) and block cosine-transform techniques have already been used together, but only to code the low-pass image. Residual spatial correlation present in higher frequencies bands has only partially been taken care of. This paper presents the results obtained with a simulated coder in which DCT is used in all bands where expected spatial correlation is high enough. The use of a pyramid vector quantizer is proposed. Results are good and compare favourably with other results published in the literature.