Prediction In Video Coding Research Articles

Statistical motion learning for improved transform domain Wyner–Ziv video coding

Wyner–Ziv (WZ) video coding is a particular case of distributed video coding (DVC), the recent video coding paradigm based on the Slepian–Wolf and Wyner–Ziv theorems which exploits the source temporal correlation at the decoder and not at the encoder as in predictive video coding. Although some progress has been made in the last years, WZ video coding is still far from the compression performance of predictive video coding, especially for high and complex motion contents. The WZ video codec adopted in this study is based on a transform domain WZ video coding architecture with feedback channel-driven rate control, whose modules have been improved with some recent coding tools. This study proposes a novel motion learning approach to successively improve the rate-distortion (RD) performance of the WZ video codec as the decoding proceeds, making use of the already decoded transform bands to improve the decoding process for the remaining transform bands. The results obtained reveal gains up to 2.3 dB in the RD curves against the performance for the same codec without the proposed motion learning approach for high motion sequences and long group of pictures (GOP) sizes.

Adaptive deblocking filter for transform domain Wyner–Ziv video coding

Wyner-Ziv (WZ) video coding is a particular case of distributed video coding, the recent video coding paradigm based on the Slepian-Wolf and Wyner-Ziv theorems that exploits the source correlation at the decoder and not at the encoder as in predictive video coding. Although many improvements have been done over the last years, the performance of the state-of-the-art WZ video codecs still did not reach the performance of state-of-the-art predictive video codecs, especially for high and complex motion video content. This is also true in terms of subjective image quality mainly because of a considerable amount of blocking artefacts present in the decoded WZ video frames. This paper proposes an adaptive deblocking filter to improve both the subjective and objective qualities of the WZ frames in a transform domain WZ video codec. The proposed filter is an adaptation of the advanced deblocking filter defined in the H.264/AVC (advanced video coding) standard to a WZ video codec. The results obtained confirm the subjective quality improvement and objective quality gains that can go up to 0.63-dB in the overall for sequences with high motion content when large group of pictures are used.

Backward channel aware Wyner–Ziv video coding: A study of complexity, rate, and distortion tradeoff

Wyner–Ziv video coding is a coding method that exploits source statistics at the decoder. Many Wyner–Ziv video coding schemes encode a video sequence into two types of frames, key frames and Wyner–Ziv frames, and rely on the frequent use of INTRA frames as key frames such that the decoder can derive sufficiently accurate side information. While the use of INTRA frame as key frames keeps the encoding complexity low, it also leads to much lower coding efficiency compared to state-of-the-art predictive video coding. In this paper we present a Wyner–Ziv video coding scheme that uses backward channel aware motion estimation to encode the key frames, where motion estimation is performed at the decoder and motion information is sent back to the encoder. Two motion vector selection methods are proposed and we present a model to study the complexity–rate–distortion tradeoff in such coding schemes.

Investigation on convergence behaviors of the differential method for 2-D motion parameter estimation

We investigate convergence behaviors of the differential method for estimation of 2-D motion parameters. While the differential method has been widely researched for motion compensated predictive video coding, little attention has been paid to its convergence properties. Based on the nonseparable exponential covariance image model, we derive theoretical estimates of update terms for translational and affine motion models. The effects of noise, spatial correlation, choice of spatial gradient measures, and the size of a region, are quantitatively analyzed in relation to the convergence speed. Some empirical results are presented to verify the analysis.

Using inter-frame dependence history to select intra-refresh blocks

To prevent error propagation in predictive video coding, intra-refresh methods are often employed. Here, a new algorithm for macroblock intra-refresh that is based on pixel level inter-frame dependence history is proposed. This new method keeps track of the coding mode of every pixel and refreshes those macroblocks that contain pixels with a long history record. Simulation results show that the new algorithm performs better than the existing methods while maintaining the same bit rate.

Error resilience of multireference motion compensated prediction in video coding

Standard coded video is vulnerable to transmission errors when transmitted over unreliable channels. The authors propose using multireference motion compensated prediction (MCP) to provide resilience to transmission errors. Both the concealment error and propagation error can be reduced in multireference MCP. First, using the multiple motion vectors associated with each coded block, a concealment scheme of low complexity with small concealment error is proposed. Then the theoretical performance limit of propagation error and coding efficiency in multireference MCP is analysed. Through a numerical solution based on the theoretical performance limit, it is found that a multireference MCP scheme can achieve greater propagation error attenuation than the traditional single-reference MCP scheme. The numerical solution also demonstrates that the performance of the multireference MCP average scheme approaches the theoretical performance limit, with coding efficiency higher than the traditional single-reference MCP scheme. Finally, results of a simulation under the assumed packet loss environment typical of the Internet are given. Simulation results demonstrate that video coding with multireference MCP performs much better than the conventional H.263 coding scheme in a lossy environment.

Optimal intra coding of blocks for robust video communication over the Internet

Abstract Reliable transmission of compressed video in a packet lossy environment cannot be achieved without error recovery mechanisms. We describe an effective method for increasing error resilience of video transmission over packet lossy networks such as the Internet. Intra coding (without reference to a previous picture) is a well-known technique for eliminating temporal error propagation in a predictive video coding system. Randomly intra coding of blocks increases error resilience to packet loss. However, when the error concealment used by the decoder is known, intra encoding following a method that optimizes the tradeoffs between compression efficiency and error resilience is a better alternative. In this paper, we present a rate-distortion optimized mode selection method for packet lossy environments that takes into account the network conditions and the error concealment method used at the decoder. We present results for different packet loss rates and typical packet sizes of the Internet, that illustrate the advantages of the proposed method.

Bidirectional variable size blockmotion compensation

The authors present a new motion compensation technique for bidirectional predictive video coding, which partitions a frame into variable size blocks according to the local motion contents and yields an optimal rate-distortion performance. Preliminary results show that this method is more efficient than the conventional fixed-size method.

Multiscale modeling and estimation of motion fields for video coding

We present a systematic approach to forward-motion-compensated predictive video coding. The first step is the definition of a flexible model that compactly represents motion fields. The inhomogeneity and spatial coherence properties of motion fields are captured using linear multiscale models. One possible design is based on linear finite elements and yields a multiscale extension of the triangle motion compensation (TMC) method. The second step is the choice of a computational technique that identifies the coefficients of the linear model. We study a modified optical flow technique and minimize a cost function closely related to Horn and Schunck's (1981) criterion. The cost function balances accuracy and complexity of the motion compensated predictor and is viewed as a measure of goodness of the motion field. It determines not only the coefficients of the model, but also the quantization method. We formulate the estimation and quantization problems jointly as a discrete optimization problem and solve it using a fast multiscale relaxation algorithm. A hierarchical extension of the algorithm allows proper handling of large displacements. Simulations on a variety of video sequences have produced improvements over TMC and over the half-pel-accuracy, full-search block matching algorithm, in excess of 0.5 dB in average. The results are visually superior as well. In particular, the reconstructed video is entirely free of blocking artifacts.