Transform Domain Energy Classification for Intra 4x4 Mode Search
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Solution Overview
Problem
The computational complexity of determining the optimal Intra 4×4 prediction mode in video coding is high due to the need to search through nine allowed modes, which is challenging for real-time systems and reduces efficiency.
Innovation Solution
An algorithm that classifies 4×4 blocks based on transform domain energy distribution into coarse classes such as DC, horizontal, vertical, diagonal, and ambiguous, reducing the search space for Intra 4×4 prediction modes, thereby reducing computational complexity while maintaining compression efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a full search of all nine Intra 4×4 prediction modes is performed to achieve optimal compression efficiency, then the compression efficiency is improved, but the computational complexity increases significantly making it unsuitable for real-time systems
Solution Approach 1:
The patent segments the nine Intra 4×4 prediction modes into five coarse classes (DC, horizontal, vertical, diagonal, and ambiguous) based on transform domain energy distribution. This segmentation allows the encoder to first classify the block into a coarse class and then perform a reduced search only within the relevant subset of modes, rather than searching all nine modes exhaustively. This resolves the contradiction by maintaining compression efficiency through systematic classification while reducing computational complexity through targeted mode search.
Solution Approach 2:
The patent performs preliminary classification of the 4×4 block into one of five coarse classes using transform domain energy distribution before conducting the mode search. This preliminary action identifies the dominant direction of energy distribution, allowing the encoder to pre-determine which subset of prediction modes is most likely to be optimal. By performing this classification beforehand, the system avoids the computational burden of searching all nine modes while still achieving near-optimal compression efficiency.
2Productivity
If the Intra 4×4 mode decision depends on reconstructed pixels of other causal 4×4 blocks to acquire optimal mode and quantization parameter, then the compression efficiency is improved, but the processing complexity and time requirements increase
Solution Approach 1:
The patent performs preliminary classification using transform domain energy distribution of the current block before considering dependencies on causal blocks. This preliminary classification provides a strong initial indication of the optimal mode based on the block's own energy characteristics, reducing the need for extensive iterative optimization that would require waiting for causal blocks to be processed. This approach maintains compression efficiency while significantly reducing processing time by establishing a near-optimal mode early in the encoding process.
Solution Approach 2:
The patent segments the mode decision process into two stages: first, a rapid classification stage based on transform domain energy distribution of the current block; second, a refined search stage that considers causal block dependencies only within the classified subset. This segmentation allows the system to quickly narrow down the search space using local block characteristics, then apply inter-block dependencies only to a small subset of candidate modes, thereby reducing overall processing time while maintaining compression efficiency.
Data Source
AI summary
This invention is method for determining direction mode for an image block in intra prediction of video frames. The method calculates a plurality of energy terms from the spatial frequency domain image block, then determines a coarse classification from these energy terms. For at least some coarse classifications the method searches from among a subset of less than all possible direction modes. The method also searches a most likely direction mode determined from neighbor blocks when available.