Chroma Intra Prediction Mode Selection for Video Coding
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Solution Overview
Problem
The existing Direct Mode (DM) in video coding standards like H.266/VVC is inadequate for chroma prediction when one chroma block corresponds to multiple luma blocks, leading to reduced accuracy in intra prediction and inefficient encoding and decoding processes.
Innovation Solution
A chroma intra prediction method that determines a set of chroma prediction modes including DM, linear mode (LM), LM_T, LM_L, DC, Planar, and diagonal angular modes, with the linear mode acquired from a bitstream, to improve chroma reconstruction accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single Direct Mode (DM) is used for chroma prediction when one chroma block corresponds to multiple luma blocks, then the encoding and decoding process is simple, but the accuracy of intra prediction is greatly reduced
Solution Approach 1:
The chroma block is divided into multiple regions corresponding to different luma blocks, and different prediction modes are applied to different regions. Specifically, when a chroma block corresponds to multiple luma blocks, the patent applies DM to some regions and horizontal/vertical prediction modes to other regions, thereby improving prediction accuracy while maintaining reasonable complexity
Solution Approach 2:
The patent dynamically selects prediction modes based on the relationship between chroma and luma blocks. When a chroma block corresponds to a single luma block, DM is used; when it corresponds to multiple luma blocks, a combination of DM and horizontal/vertical modes is used. This dynamic adaptation resolves the contradiction between simplicity and accuracy
2Ease of manufacture
If only DC mode or Planar mode is used as DM for chroma prediction, then the prediction process is simple, but it fails to capture local texture features in non-flat regions
Solution Approach 1:
The patent changes the prediction mode parameters dynamically based on the flatness of the luma blocks. When luma blocks are flat, DC or Planar modes are used; when they are not flat, horizontal or vertical modes are introduced. This parameter adaptation maintains simplicity in flat regions while improving reliability in textured regions
3Adaptability or versatility
If horizontal and vertical prediction directions are used as default candidates, then the candidate positions are utilized, but chroma blocks entirely conforming to these directions are very few, wasting candidate positions
Solution Approach 1:
The patent applies different prediction modes to different local regions of the chroma block based on the characteristics of corresponding luma blocks. Horizontal and vertical modes are applied only to regions where they are appropriate (non-flat luma blocks), while DM is applied to regions where it is more suitable (flat luma blocks), optimizing both adaptability and efficiency
Data Source
AI summary
Chroma intra prediction methods and devices are provided. The method includes: determining a direct mode (DM) corresponding to a current chroma block; determining an intra prediction mode of the current chroma block from a set of chroma prediction modes, wherein the set of chroma prediction modes comprises at least one of the DM, linear mode (LM), LM_T or LM_L, wherein when a luma prediction mode corresponding to the DM is a direct current (DC) mode or a planar mode, the set of chroma prediction modes comprises a diagonal angular mode with prediction direction index number 66, wherein the linear mode is acquired from a bitstream before determining the set of chroma prediction modes; and determining a reconstructed value of the current chroma block according to the intra prediction mode.