Adaptive Wide-Angle Intra Prediction for Rectangular Video Blocks
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Solution Overview
Problem
The current Versatile Video Compression (VVC) standard's wide-angle intra prediction (WAIP) is suboptimal for rectangular blocks due to prediction angles derived from square block shapes, leading to inefficient reference array lengths and redundant samples, especially for blocks with aspect ratios other than 4:1, resulting in poor compression efficiency.
Innovation Solution
The proposed solution involves increasing the number of wide angles in proportion to the aspect ratio of rectangular blocks, aligning prediction directions with the secondary diagonal, and adjusting reference array lengths to twice the block side length, eliminating the need for extensions and reducing redundancy, thereby optimizing prediction accuracy for all rectangular block shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the current VVC standard's wide-angle intra prediction is used with fixed prediction angles derived from square block shapes, then the implementation is simple, but the compression efficiency deteriorates for rectangular blocks with aspect ratios other than 4:1
Solution Approach 1:
The patent applies dynamics by making the prediction angles adaptive rather than fixed. The prediction angles are dynamically adjusted based on the aspect ratio of the rectangular block, allowing the system to optimize for different block shapes while maintaining a unified framework. This resolves the contradiction by enabling compression efficiency to improve with aspect ratio variations without significantly complicating the implementation.
Solution Approach 2:
The patent changes the parameters of the prediction angles based on the block's aspect ratio. Instead of using fixed angles derived from square blocks, the prediction angles are modified as a function of the aspect ratio, allowing the system to adapt to different rectangular block shapes. This parameter adjustment improves compression efficiency while keeping the overall method relatively simple.
2Stability of the object's composition
If the reference array lengths are not adjusted for different aspect ratios, then the implementation is consistent, but redundant samples increase and prediction accuracy deteriorates
Solution Approach 1:
The patent applies local quality by adjusting the reference array lengths according to the specific aspect ratio of each block. Instead of using a uniform reference array length for all blocks, the system tailors the reference array length to match the local characteristics of each rectangular block, thereby eliminating redundant samples and improving prediction accuracy for each specific case.
Solution Approach 2:
The reference array length is made dynamic rather than static. It changes based on the aspect ratio of the block being processed, allowing the system to optimize the reference array length for each specific block shape. This dynamic adjustment improves prediction accuracy while maintaining implementation consistency through a unified adaptive approach.
3Adaptability or versatility
If the number of wide angles is not increased in proportion to aspect ratio, then the prediction coverage is sufficient for square blocks, but prediction accuracy deteriorates for rectangular blocks
Solution Approach 1:
The patent changes the number of wide angles as a parameter that depends on the aspect ratio. By increasing the number of wide angles in proportion to the aspect ratio, the system adapts the prediction coverage to match the block's dimensions, thereby improving prediction accuracy for rectangular blocks while maintaining sufficient coverage for square blocks.
Solution Approach 2:
The number of wide angles is made dynamic rather than fixed. It adjusts according to the aspect ratio of the block, allowing the system to provide appropriate prediction coverage for different block shapes. This dynamic adjustment ensures that prediction accuracy is optimized for each specific aspect ratio while maintaining overall versatility.
Data Source
AI summary
Methods and apparatus for using wide-angle intra prediction for rectangular blocks enable greater prediction angles. Wide-angle intra prediction enables intra prediction direction angles beyond the conventional 45 and −135 degrees. In one embodiment, when a video block to be coded or decoded is non-square, additional intra prediction directions are enabled in the direction of the longer block edge and more reference samples are available along that edge. An index is used to indicate the prediction direction and can be adapted according to the additional intra predictions in the longer direction, with correspondingly fewer prediction directions along the shorter block edge. This preserves the number of prediction modes that need to be indexed but allows their angles to correspond to the shape of the block.