Intra Prediction Angle Mapping for Non-Square Video Blocks
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Solution Overview
Problem
In the luma and chroma prediction processes of the next generation video coding standard H.266/VVC, the use of wide angular modes leads to deviations in angular mode representation, affecting the accuracy of intra prediction due to different actual angles corresponding to the same mode index, and complicates angle conversion.
Innovation Solution
An intra prediction method that configures actual angular modes using relative angle numbers, determined by preset angle sampling points and width-height relationships, ensuring a one-to-one correspondence with actual angular modes, thereby simplifying angle conversion and improving prediction accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wide angular modes are used in luma prediction to reduce bits for entropy coding, then coding efficiency is improved, but angular mode representation accuracy deteriorates due to different actual angles corresponding to the same mode index
Solution Approach 1:
The patent introduces a parameter transformation approach by mapping angular mode indices to actual angle values through a conversion formula. The angular mode index is transformed into an actual angle parameter that accurately represents the prediction direction, resolving the contradiction between coding efficiency and representation accuracy.
Solution Approach 2:
The patent uses an intermediary conversion mechanism between angular mode indices and actual angle values. This intermediary layer (the angle conversion formula) mediates between the compressed angular mode indices and the accurate actual angles, allowing both efficient coding and accurate representation.
2Device complexity
If angular modes with the same number are used in MPM list for neighbouring blocks, then encoding complexity is reduced, but prediction accuracy deteriorates due to different actual angles for non-square blocks
Solution Approach 1:
The patent applies parameter transformation to convert angular mode indices to actual angle values specific to each block's geometry. This ensures that the same MPM list index corresponds to different actual angles for different block shapes, maintaining prediction accuracy without increasing encoding complexity.
Solution Approach 2:
The patent implements local adaptation by allowing the angular mode interpretation to vary according to each block's local properties (width-height ratio). Each block uses its specific geometric characteristics to determine the actual angle corresponding to a given mode index, ensuring locally accurate prediction while using a unified MPM list structure.
3Ease of manufacture
If direct mode borrows angular mode index from luma block in chroma prediction, then processing simplicity is improved, but prediction accuracy deteriorates due to deviation between borrowed and actual angular modes
Solution Approach 1:
The patent introduces an intermediary conversion step in the chroma prediction process. Instead of directly borrowing the angular mode index, the system converts the luma block's angular mode index to its actual angle value, then uses this accurate angle for chroma prediction, eliminating the deviation while maintaining processing simplicity.
Solution Approach 2:
The patent replaces the direct mechanical copying of angular mode indices with a computational transformation process. The angular mode index is substituted with a calculated actual angle value derived from the index and block geometry, improving accuracy without significantly increasing processing complexity.
Data Source
AI summary
A method for intra prediction and a non-transitory computer-readable storage medium are provided. The method includes the following operations. A first intra prediction mode index of at least one neighbouring block of a current block is determined, and an intra prediction mode list corresponding to the current block is constructed based on the first intra prediction mode index of the at least one neighbouring block. A first intra prediction mode index of the current block is determined based on the intra prediction mode list. A width to height ratio of the current block is obtained, and the first intra prediction mode index is mapped to a second intra prediction mode index according to the width to height ratio. Prediction is performed for the current block based on a target intra prediction mode, and a prediction block is obtained.