Intra Prediction Coding: Aspect-Ratio Wide-Angle Modes
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Solution Overview
Problem
Existing video coding standards like HEVC and VVC face inefficiencies in signaling intra prediction modes due to high bit costs and correlations between neighboring blocks, particularly with the increasing number of intra prediction modes in VVC Draft 2.
Innovation Solution
The proposed solution involves determining the aspect ratio of a coding unit and adding specific intra prediction modes, such as wide angles towards the unit's edges, to a table for signaling, thereby optimizing mode selection based on block relationships and reducing bit usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of intra prediction modes is increased to improve prediction accuracy, then the prediction accuracy is improved, but the bit cost for signaling increases
Solution Approach 1:
The patent applies local quality by differentiating the treatment of intra prediction modes based on their probability. High-probability modes (MPMs) are signaled using unary code while low-probability modes use fixed-length coding. Additionally, the patent selectively adds wide-angle modes only when needed based on aspect ratio, optimizing the balance between prediction accuracy and signaling cost for different local conditions.
Solution Approach 2:
The patent changes the parameter of mode signaling by introducing aspect ratio-based selection for adding wide-angle modes. The system dynamically adjusts the set of available intra prediction modes based on the coding unit's aspect ratio, and modifies the signaling method based on mode probability, thereby optimizing the trade-off between accuracy and bit cost.
2Adaptability or versatility
If more intra prediction modes are added to handle various block shapes, then the adaptability to different block shapes is improved, but the complexity of mode selection increases
Solution Approach 1:
The patent applies local quality by tailoring the set of available intra prediction modes to the specific characteristics of each coding unit. Wide-angle modes are added only when the aspect ratio indicates a need for such modes, creating a localized adaptation that maintains versatility while avoiding unnecessary complexity in square blocks.
Solution Approach 2:
The patent introduces dynamics by making the set of available intra prediction modes variable rather than fixed. The system dynamically adjusts which modes are available based on the coding unit's aspect ratio, allowing flexible adaptation to different block shapes while managing complexity through conditional inclusion.
3Measurement precision
If wide-angle modes are added for non-square blocks, then the prediction accuracy for non-square blocks is improved, but the bit cost increases
Solution Approach 1:
The patent applies local quality by selectively adding wide-angle modes only to coding units with non-square aspect ratios where they are actually needed. This localized approach ensures improved prediction accuracy for non-square blocks while avoiding the bit cost increase that would result from universally adding all wide-angle modes regardless of block shape.
Solution Approach 2:
The patent applies partial action by adding wide-angle modes only when necessary (for non-square blocks) rather than excessively adding them to all blocks. This selective inclusion optimizes the balance between improving prediction accuracy for the target case and avoiding unnecessary bit cost increases.
Data Source
AI summary
A method of and an apparatus for controlling intra prediction for encoding of a video sequence are provided. The method includes determining a ratio of a width to a height of a coding unit, and based on the determined ratio being different than one, adding, to a table including intra prediction modes corresponding to intra prediction angles, first wide angles toward a bottom-left edge of the coding unit, second wide angles toward a top-right edge of the coding unit, and additional intra prediction modes respectively corresponding to the first wide angles and the second wide angles. The method further includes signaling, for encoding the video sequence, one of the intra prediction modes and the additional intra prediction modes added to the table.