Intra Chroma Prediction Mode Coding Adaptation
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Solution Overview
Problem
Current video coding standards, such as H.264/AVC and HEVC, face inefficiencies in coding intra chroma prediction modes due to the high bitrate required for conveying side information, especially for smaller chroma block sizes, which affects the overall coding efficiency.
Innovation Solution
The method involves assigning a shortest variable length code to the Luma_mode for intra chroma prediction, adapting the coding table based on frequent modes, and using context information from neighboring blocks for arithmetic coding to reduce the total number of variable length codes and their maximum length, thereby improving coding efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If variable length codes are used to code intra chroma prediction mode in H.264/AVC and HEVC standards, then coding flexibility is improved, but the bitrate becomes substantial for small chroma blocks
Solution Approach 1:
The patent applies local quality by using different coding strategies for different chroma block sizes. For small chroma blocks (4x4, 8x8), a simplified coding table with fewer modes is used, while for larger blocks (16x16), the full set of intra prediction modes is available. This localized adaptation reduces the bitrate for small blocks while maintaining coding flexibility for larger blocks where it is more beneficial.
Solution Approach 2:
The patent changes the parameter of the coding table itself by providing different tables based on block size and luma prediction mode. The coding table is transformed from a fixed structure to a variable structure that adapts to local conditions, reducing the number of bits required to encode chroma prediction modes for small blocks while preserving full mode availability when needed.
2Measurement precision
If multiple intra prediction modes are provided for chroma components, then prediction accuracy is improved, but the side information to be conveyed increases
Solution Approach 1:
The patent applies preliminary action by pre-defining multiple coding tables with different mode sets, and selecting the appropriate table before encoding based on block size and luma mode. This preliminary preparation allows the encoder to optimize the balance between prediction accuracy and side information without complex runtime decisions, reducing the overhead while maintaining accuracy where beneficial.
Solution Approach 2:
The patent segments the set of intra prediction modes into different groups based on block size. For small chroma blocks, only a subset of modes (e.g., vertical, horizontal, DC) is included in the coding table, while larger blocks can access the full mode set. This segmentation reduces the side information for small blocks while preserving prediction accuracy options for larger blocks that benefit from more modes.
3Volume of moving object
If chroma block size is reduced for higher resolution, then spatial resolution is improved, but the coding efficiency of intra prediction mode becomes more critical due to smaller block sizes
Solution Approach 1:
The patent applies local quality by tailoring the prediction mode coding strategy to each chroma block size. For small blocks resulting from high-resolution scaling, a simplified coding table with fewer modes is used, reducing the bitrate overhead. For larger blocks, the full mode set is available to maintain prediction accuracy. This localized adaptation ensures coding efficiency is optimized for each block size while supporting high overall spatial resolution.
Data Source
AI summary
A method and apparatus for improved intra chroma prediction mode coding are disclosed. Intra prediction exploits the spatial correlation within a picture or within a picture region. In practice, a picture is divided into blocks and the intra mode prediction is performed on a block basis. In newer coding systems, multiple intra coding modes such as Vertical mode, Horizontal mode, DC mode and Diagonal mode, have been used to improve the coding efficiency of intra coding. Furthermore, a Luma_mode has also been used in intra prediction of chroma component to further improve the performance in the High Efficiency Video Coding (HEVC) standard being developed. However, the mode selection information for intra prediction has to be conveyed to the decoder for proper operation. Spatial features in a picture often exist in both luma and chroma components. The intra luma prediction mode and intra chroma prediction mode will have high probability to be the same. Accordingly, an embodiment according to the present invention adaptively assigns variable length codes to a set of mode symbols associated with intra chroma prediction by assigning a shortest code to the Luma_mode. Luma_mode not only can be the best luma mode of the corresponding luma block but also can be selected from several corresponding luma modes. The maximum length of chroma prediction codes is decreased by one bit when Luma_mode is equal to one of frequent modes. The coding efficiency of arithmetic coding of chroma prediction codes is further improved by selecting the context upon neighboring blocks.