Chroma Intra Prediction Mode Segmentation for Video Coding Efficiency
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Solution Overview
Problem
The existing High Efficiency Video Coding (HEVC) standard has limited flexibility and coding efficiency for chroma Intra prediction, particularly in high-quality videos with abundant colors, due to a restricted set of chroma Intra prediction modes and inefficient signaling methods.
Innovation Solution
The proposed method enhances chroma Intra prediction by increasing the number of available modes to more than six, including additional angular prediction modes, and adapts the number of modes based on block size, allowing for variable chroma Intra prediction modes between 9 and 67, and employs a most-probable-mode (MPM) process for efficient signaling using flags and context-based coding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the number of chroma Intra prediction modes is limited to six as in HEVC, then the signaling complexity is reduced, but the coding efficiency and flexibility for high-quality videos with abundant colors deteriorates
Solution Approach 1:
The chroma Intra prediction modes are segmented into two groups: Most Probable Modes (MPM) and remaining modes. The MPM list contains the most frequently used modes (including DC, planar, and selected angular modes), while remaining modes cover less frequent cases. This segmentation allows the encoder to signal only the index within the MPM list when applicable, reducing signaling complexity while maintaining access to a total of 67 chroma Intra prediction modes for high coding efficiency.
Solution Approach 2:
The size of the chroma Intra prediction mode set is made dynamic and adaptable based on block size and video content characteristics. For different block sizes (e.g., 8x8, 16x16, 32x32, 64x64), different numbers of angular prediction modes are selected (ranging from 9 to 67 modes). This dynamic adaptation allows the system to optimize between signaling complexity and coding efficiency according to specific video content requirements.
2Productivity
If more than six chroma Intra prediction modes are provided to improve coding efficiency, then the ability to handle diverse video content is improved, but the signaling complexity and computational load increases
Solution Approach 1:
The Most Probable Mode (MPM) list is pre-computed and prepared before the actual prediction process. The MPM list includes modes that are statistically most likely to be used for chroma Intra prediction, such as DC mode, planar mode, and specific angular modes derived from neighboring blocks. By having this list pre-prepared, the encoder can quickly determine whether to use an MPM mode without extensive computation during encoding, thus reducing real-time signaling complexity while maintaining access to a large mode set for high coding efficiency.
Solution Approach 2:
The system changes the parameter of mode selection by using context-based coding for MPM indices and flags. Instead of signaling all 67 modes explicitly, the encoder transmits a flag indicating whether an MPM mode is used, and if so, the index within the MPM list. This parameter change in signaling methodology dramatically reduces the bitstream complexity while preserving the ability to select from numerous prediction modes for optimal coding efficiency.
3Ease of manufacture
If a fixed set of six chroma Intra prediction modes is used, then the encoder implementation is simpler, but the adaptability to different block sizes and video characteristics deteriorates
Solution Approach 1:
The chroma Intra prediction system is designed with universal adaptability to handle multiple block sizes (8x8, 16x16, 32x32, 64x64) and various video characteristics using a unified framework. The same MPM list construction and mode selection mechanism applies across all block sizes, with the only variation being the number of angular modes selected based on block size. This universal approach maintains encoder implementation simplicity while achieving high adaptability to different video content and block size requirements.
Solution Approach 2:
The system uses parameter changes to adapt the number of angular prediction modes based on block size. For smaller blocks (e.g., 8x8), fewer angular modes (e.g., 9 modes) are selected to reduce complexity, while for larger blocks (e.g., 64x64), more angular modes (e.g., 67 modes) are available to capture finer directional variations. This parameter-based adaptation allows a single encoder implementation to efficiently handle diverse block sizes and video characteristics without requiring multiple specialized code paths.
Data Source
AI summary
A method and apparatus for chroma Intra prediction are disclosed. According to one method, a chroma Intra mode set comprising more than six chroma Intra coding modes are generated and chroma Intra-prediction encoding or decoding is applied to the current chroma block using a current chroma Intra mode selected from the chroma Intra mode set. According to another method, a chroma MPM list is determined and a current chroma Intra mode is signaled using chroma MPM process at the video encoding system or parsing the current chroma Intra mode using the chroma MPM process at the video decoding system, where the chroma MPM process comprises using a chroma MPM flag to indicate whether the current chroma Intra mode belongs to the chroma MPM list.