Abstract

Hybrid video coding combines together two stages: first, motion estimation and compensation predict each frame from the neighboring frames, then the prediction error is coded, reducing the correlation in the spatial domain. In this work, we focus on the latter stage, presenting a scheme that profits from some of the features introduced by the standard H.264/AVC for motion estimation and replaces the transform in the spatial domain. The prediction error is so coded using the matching pursuit algorithm which decomposes the signal over an appositely designed bidimensional, anisotropic, redundant dictionary. Comparisons are made among the proposed technique, H.264, and a DCT-based coding scheme. Moreover, we introduce fast techniques for atom selection, which exploit the spatial localization of the atoms. An adaptive coding scheme aimed at optimizing the resource allocation is also presented, together with a rate-distortion study for the matching pursuit algorithm. Results show that the proposed scheme outperforms the standard DCT, especially at very low bit rates.

Highlights

  • The most successful class of video compression algorithms is based on hybrid methods consisting in the combination of prediction loops in the temporal dimension with a suitable uncorrelation technique in the spatial domain.The state of the art for hybrid video coding is specified by the recent standard H.264, named advanced video coding (AVC)

  • We aim at exploiting the advantages of coding the displaced frame difference (DFD), output of the motion compensation (MC) algorithm, using a redundant dictionary

  • We did not disable all the features missing in our MC algorithm and this results in a not completely fair comparison between the two approaches

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Summary

INTRODUCTION

The most successful class of video compression algorithms is based on hybrid methods consisting in the combination of prediction loops in the temporal dimension (motion estimation/motion compensation) with a suitable uncorrelation technique in the spatial domain (transform coder). We aim at exploiting the advantages of coding the displaced frame difference (DFD), output of the motion compensation (MC) algorithm, using a redundant dictionary. This kind of dictionaries leaves more freedom to the basis functions design and they can be created with the goal of catching the structures of DFDs. In order to remain as close as possible to the state of the art, we adopt a motion estimation algorithm that is compatible with H.264 (see Section 2).

MOTION ESTIMATION
CODING DISPLACED FRAME DIFFERENCES
Greedy algorithms
Matching pursuit
Dictionary design
Atom selection
QUANTIZATION AND ENTROPY CODING
An adaptive solution
RATE-DISTORTION OPTIMIZATION
RESULTS AND COMPARISONS
CONCLUSIONS
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