Video Decoder Post-Processing for Range Limit Violations
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Solution Overview
Problem
Video encoding processes often violate original range limits of picture samples due to lossy compression, leading to inaccuracies and inefficiencies in reconstructed/decoded pictures, which can propagate as encoding drift artifacts.
Innovation Solution
Implementing post-processing techniques such as clipping, filtering, or offsetting for prediction or decoded units, using correspondence functions that adjust values of one color component based on another, to maintain or restore the original range limits and improve picture quality and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If lossy compression is applied to reduce data amount, then data compression efficiency is improved, but picture sample accuracy deteriorates due to range limit violations
Solution Approach 1:
The patent applies clipping operations as a post-processing step after decoding to preliminarily correct range limit violations before the reconstructed samples are used for prediction. This preliminary correction prevents accuracy deterioration while maintaining compression efficiency.
Solution Approach 2:
The patent implements a feedback mechanism where the decoder detects range limit violations in reconstructed samples and applies corrective clipping operations. The clipped samples are then fed back into the prediction process, creating a closed-loop system that maintains accuracy without sacrificing compression efficiency.
2Device complexity
If fixed a priori clipping tests are applied, then device complexity is reduced, but picture quality deteriorates due to original range limit constraint violations
Solution Approach 1:
The patent applies different clipping strategies to different components (luma and chroma) and different prediction types (intra and inter prediction). This local quality approach ensures that clipping is applied where necessary to maintain picture quality without unnecessarily increasing device complexity in areas where it is not needed.
Solution Approach 2:
The patent dynamically adjusts clipping parameters based on the prediction mode and component type. By changing parameters adaptively rather than using fixed thresholds, the patent maintains picture quality while avoiding the complexity of more sophisticated adaptive clipping algorithms.
3Productivity
If reconstructed picture samples with violated range limits are used as predictors, then coding efficiency is reduced due to encoding drift artifacts, but using additional correction processes increases device complexity
Solution Approach 1:
The patent implements self-service clipping where the decoding process automatically corrects its own range limit violations. The clipped reconstructed samples are then used for prediction, creating a self-correcting system that maintains coding efficiency without requiring external correction processes or increased device complexity.
Data Source
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AI summary
Methods and devices for encoding and decoding a sequence of pictures, and corresponding computer program product and computer-readable medium. The disclosure relates to a method for decoding a video stream representative of a sequence of pictures, comprising: - obtaining (22) at least a first color component and a second color component of a picture unit, - decoding (23) at least one parameter of a post-processing of the second component, said at least one parameter being defined as a function of the first color component, - applying (24) said at least one post-processing to the second color component of the picture unit responsive to said at least one decoded parameter and to said first color component.