Chroma Intra Prediction Mode Adaptation for Aspect-Ratio Mismatch
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Solution Overview
Problem
Existing video compression techniques, such as H.264/AVC, HEVC, and VVC, face inefficiencies in encoding chroma blocks due to the limited use of directional modes in DM mode, which affects encoding efficiency and video quality.
Innovation Solution
Adaptive modification of luma block directional modes based on chroma block characteristics, including position, size, and reference samples, to enhance intra prediction for chroma signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DM mode is used for chroma block intra prediction, then encoding efficiency is improved, but prediction accuracy deteriorates when luma block and chroma block have different aspect ratios
Solution Approach 1:
The patent applies local quality by determining whether to modify the luma block's directional mode separately for each chroma block based on its aspect ratio. When the chroma block's aspect ratio differs from the luma block's, the directional mode is selectively modified only for those specific cases, rather than applying a uniform rule to all chroma blocks. This localized adaptation resolves the contradiction by improving prediction accuracy where needed while maintaining encoding efficiency elsewhere.
Solution Approach 2:
The patent implements dynamics by making the directional mode modification adaptive rather than fixed. The system dynamically adjusts the luma block's directional mode based on real-time comparison of aspect ratios between luma and chroma blocks. This dynamic adjustment allows the system to respond to varying block geometries, resolving the prediction accuracy issue while preserving the encoding efficiency benefits of DM mode.
2Device complexity
If luma block directional mode is used for chroma block prediction, then encoding complexity is reduced, but prediction quality deteriorates when aspect ratios differ
Solution Approach 1:
The patent applies local quality by implementing selective modification only when necessary. The system compares aspect ratios of luma and chroma blocks and modifies the directional mode only for chroma blocks with different aspect ratios, leaving other cases unchanged. This localized approach maintains low encoding complexity for the majority of cases while improving prediction quality specifically where aspect ratio mismatches occur.
Solution Approach 2:
The patent changes the parameter of directional mode based on the aspect ratio parameter. When the aspect ratio of a chroma block differs from its corresponding luma block, the system modifies the directional mode parameter to accommodate the different geometry. This parameter change resolves the prediction quality issue while adding minimal complexity, as it only activates when aspect ratios differ.
3Speed
If fixed directional mode is used for chroma blocks, then processing speed is maintained, but encoding efficiency deteriorates with varying block sizes and positions
Solution Approach 1:
The patent implements dynamics by transitioning from a fixed directional mode to an adaptive one that adjusts based on block characteristics. The system compares aspect ratios of luma and chroma blocks and modifies the directional mode accordingly. This dynamic adjustment improves encoding efficiency for varying block sizes and positions while maintaining processing speed, as the modification logic is applied only when necessary and uses simple aspect ratio comparison.
Data Source
AI summary
A video encoding method and a video decoding method are provided for adaptively determining a chroma intra-directional prediction mode. When a DM mode is applied for intra prediction of a chroma signal, the video encoding method and the video decoding method adaptively modify the directional mode of a luma block to conform to the characteristics of a chroma block by considering the position and size of the chroma block, the presence of reference samples, and the size of the luma block. The video encoding method and the video decoding method use the modified directional mode for intra prediction of the chroma signal.