Wide-Angle Intra Prediction for Accurate Non-Square Block Coding
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Solution Overview
Problem
Existing video compression standards inefficiencies arise from angular intra prediction directions that are not adapted to the shape of non-square video blocks, leading to asymmetry and inaccurate prediction modes, particularly in rectangular blocks.
Innovation Solution
Adapt intra prediction directions based on the shape of the video block, modifying the number and arrangement of prediction modes for rectangular blocks, and extending position-dependent intra prediction combination (PDPC) to wide-angle modes, ensuring efficient use of reference samples.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional angular intra prediction directions are used for non-square video blocks, then the encoding process is simple, but the prediction accuracy deteriorates due to asymmetry and inaccuracy in rectangular blocks
Solution Approach 1:
The patent applies local quality by adapting the intra prediction direction selection to the specific shape characteristics of each video block. Different prediction modes are selected based on the block's aspect ratio and orientation, ensuring that each local region uses the most appropriate prediction direction rather than a uniform approach across all blocks
Solution Approach 2:
The patent introduces dynamic adaptation of prediction modes based on block shape parameters. The system dynamically selects from multiple prediction direction sets (e.g., horizontal, vertical, diagonal, and wide-angle modes) depending on the block's aspect ratio and orientation, making the prediction process adaptive rather than static
2Productivity
If standard intra prediction modes are used for all block shapes, then the encoding complexity is low, but the compression efficiency deteriorates due to inaccurate prediction of non-square blocks
Solution Approach 1:
The patent changes the prediction mode parameters based on block shape characteristics. By modifying which prediction directions are considered and how reference samples are weighted according to the block's aspect ratio and orientation, the system optimizes compression efficiency for different block geometries without requiring a complete redesign of the prediction framework
3Measurement precision
If asymmetric prediction modes are introduced for rectangular blocks, then the prediction accuracy for non-square blocks improves, but the symmetry and uniformity of the prediction system deteriorates
Solution Approach 1:
The patent deliberately introduces asymmetry into the prediction system by providing different prediction mode sets for different block orientations and aspect ratios. Rather than maintaining artificial symmetry, the system accepts and utilizes the inherent asymmetry of rectangular blocks to improve prediction accuracy, with separate handling for horizontal, vertical, and diagonal rectangular blocks
Data Source
AI summary
Methods and apparatus for performing intra prediction in an encoder or a decoder for non-square blocks enable a combination of reference samples from a row above the non-square block and a row to the left of the non-square block to be used for the prediction. In one embodiment, a weighted combination of reference samples are used. In another embodiment, the angles of prediction are extended in the longer direction of the non-square block, such that less angles of prediction are used in the shorter direction.