VVC Chroma Intra Prediction via Decoder-Side Texture Gradients
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Solution Overview
Problem
The VVC and ECM video coding standards face challenges in accurately predicting chroma blocks due to the increased bit signaling and reduced accuracy of Direct Mode when more angular intra prediction modes are added, especially for very small luma blocks, leading to inefficiencies in matching texture characteristics.
Innovation Solution
A decoder-side chroma intra prediction mode is derived using gradient-based methods, computing texture gradients of adjacent luma and chroma samples to determine the intra prediction mode without needing to signal it in the bitstream, allowing for improved coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If more angular intra prediction modes are added to capture arbitrary edge directions, then prediction accuracy for luma blocks is improved, but the number of bits signaled in the bitstream increases
Solution Approach 1:
The patent extracts the chroma intra prediction mode derivation from the bitstream signaling process. Instead of signaling the chroma mode separately, the system derives it from the luma block's prediction mode and texture gradient information, eliminating the need for additional chroma mode signaling bits while maintaining prediction accuracy
Solution Approach 2:
The luma block's intra prediction mode is made universal by using it to derive both the luma prediction and the chroma prediction mode. The same luma mode information, combined with texture gradient analysis, serves dual purposes for predicting both luma and chroma components, reducing overall signaling requirements
2Adaptability or versatility
If more intra prediction modes are provided for luma blocks, then luma prediction capability is improved, but chroma prediction accuracy deteriorates due to reduced Direct Mode accuracy
Solution Approach 1:
The patent applies local quality by analyzing texture gradients specific to each chroma block's location and characteristics. Instead of using a generic derivation method, the system computes texture gradients from adjacent luma and chroma samples specific to the current chroma block's context, enabling accurate chroma prediction that adapts to local texture characteristics
Solution Approach 2:
The patent introduces texture gradient computation as an intermediary mechanism between the luma prediction mode and chroma prediction. The texture gradient serves as a mediator that translates luma block characteristics into appropriate chroma prediction modes, bridging the gap between luma versatility and chroma accuracy requirements
3Ease of manufacture
If Direct Mode is used for chroma prediction, then coding simplicity is maintained, but accuracy deteriorates for very small luma blocks
Solution Approach 1:
The patent applies dynamics by making the chroma prediction mode derivation adaptive to the luma block size. The system dynamically adjusts the derivation process based on whether the luma block is small or large, using texture gradient analysis for small blocks where Direct Mode fails, while maintaining Direct Mode for larger blocks where it remains accurate, thus optimizing performance across different block sizes
Data Source
AI summary
A VVC-standard encoder and a VVC-standard decoder are provided, implementing a decoder-side chroma intra prediction mode gradient-based derivation method, which improves coding efficiency of chroma intra prediction, thereby saving on signaling cost. A VVC-standard decoder configures one or more processors of a computing system to derive one of multiple possible chroma intra prediction modes by computing gradients of adjacent luma samples and chroma samples of a current chroma block. With minimal increase in signaling cost, the VVC-standard coding and decoding processes are enhanced to base intra prediction modes for chroma blocks on collocated luma block-adjacent reconstructed luma samples adjacent reconstructed chroma samples, enabling prior computational work done on coding and decoding adjacent blocks to be referenced. In this fashion, coding gains can be achieved in matching texture characteristics of the current chroma block based on a texture gradient including adjacent blocks.