Intra Prediction Mode Distribution for Video Compression
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Solution Overview
Problem
The existing video coding standards, such as HEVC and JEM, have limitations in directional intra prediction modes, particularly for rectangular blocks, where the number of modes is not optimized, and the use of reference samples is not symmetric, leading to suboptimal compression efficiency.
Innovation Solution
The method adjusts the total number of intra prediction modes for a current block to ensure that the number of non-Most Probable Modes (non-PMMs) is a power of 2 or a sum of multiple powers of 2, allowing for more flexible and efficient coding by modifying the mode distribution and utilizing asymmetric intra angular prediction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of directional intra prediction modes is increased from 35 to 67 to capture arbitrary edge directions, then the compression efficiency is improved, but the device complexity and coding overhead increase
Solution Approach 1:
The patent divides the 67 intra prediction modes into two distinct groups: MPM (Most Probable Mode) modes and non-MPM modes. The MPM group contains 35 modes that are most likely to occur and are coded with higher priority, while the non-MPM group contains the remaining modes. This segmentation allows the encoder to focus computational resources on the most important modes while still supporting the full range of 67 modes, thereby improving compression efficiency without proportionally increasing device complexity.
Solution Approach 2:
The patent introduces a mode classification parameter that distinguishes between MPM and non-MPM modes. This parameter change enables different coding strategies for different mode groups: MPM modes use a more efficient coding approach with lower overhead, while non-MPM modes use a standard coding approach. This parameter-based differentiation resolves the contradiction by allowing the system to achieve high compression efficiency for the majority of cases (MPM modes) while maintaining support for all 67 modes.
2Reliability
If asymmetric intra angular prediction is implemented to optimize mode distribution, then the compression capability is enhanced, but the device complexity increases
Solution Approach 1:
The patent implements asymmetric intra angular prediction by treating horizontal and vertical directions differently in the mode distribution. Specifically, the MPM mode selection and ordering is optimized to reflect the statistical asymmetry in natural video content, where horizontal and vertical edges occur with different frequencies. This asymmetric approach enhances compression capability by better matching the actual distribution of edge directions in video content, while the asymmetry is carefully designed to avoid excessive increases in device complexity through efficient data structures and algorithms.
3Reliability
If the intra mode coding method with 6 MPMs is used to accommodate increased directional modes, then the compression efficiency is improved, but the entropy coding complexity increases
Solution Approach 1:
The patent segments the 67 intra prediction modes into MPM modes (35 modes) and non-MPM modes (32 modes). The entropy coding process is correspondingly segmented into two stages: first, select one of the 6 MPM modes using a simplified entropy coding process; second, if needed, select from the remaining non-MPM modes using a standard entropy coding process. This segmentation of the entropy coding process reduces the overall coding complexity compared to directly coding from all 67 modes, while still achieving high compression efficiency through the MPM approach.
Solution Approach 2:
The patent applies different entropy coding quality levels to different mode groups. MPM modes, which are most probable, receive more sophisticated entropy coding treatment with 6 context-adaptive binary arithmetic coding (CABAC) contexts to achieve high compression efficiency. Non-MPM modes use a simpler entropy coding approach. This local quality differentiation optimizes the balance between compression efficiency and coding complexity by applying high-quality coding only where it provides the most benefit.
Data Source
AI summary
A method of and an apparatus for controlling intra and/or inter prediction for decoding of a video sequence are provided. The method includes determining a total number of intra prediction modes for a current block, a number of Most Probable Modes (MPMs) in the current block, and a number of non-MPMs in the current block, wherein the total number of intra prediction modes for the current block is equal to a sum of the number of MPMs in the current block and the number of non-MPMs in the current block. The method further includes adjusting the total number of intra prediction modes to a value such that the number of non-MPMs is a power of 2 or a sum of multiple power of 2.