Intra Prediction Mode Coding with Variable Length Non-MPM Indices
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Solution Overview
Problem
The existing HEVC standard's intra prediction mode coding is inefficient due to limited prediction angles and inaccurate probability distribution modeling, leading to increased encoder complexity and suboptimal compression efficiency.
Innovation Solution
Deriving more than three Most Probable Modes (MPMs) for intra prediction, using context modeling, and encoding non-MPM indices with variable length codes based on criteria to reduce bitstream size and improve prediction accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If more than three Most Probable Modes (MPMs) are derived for intra prediction, then prediction accuracy is improved, but encoder complexity increases
Solution Approach 1:
The intra prediction modes are segmented into MPM modes and non-MPM modes. The encoder derives M most probable modes (where M > 3) from the available intra prediction modes and selectively codes only when the actual mode matches one of the MPMs, thereby improving prediction accuracy while controlling encoder complexity through conditional processing.
Solution Approach 2:
The patent changes the parameter M (number of MPMs) from the conventional 3 to a value greater than 3. This parameter change allows the system to derive and code more probable modes, improving prediction accuracy. The syntax element design and conditional coding approach ensure that this parameter change does not excessively increase encoder complexity.
2Loss of substance
If variable length codes are used for non-MPM indices, then bitstream size is reduced, but decoding complexity increases
Solution Approach 1:
The patent applies variable length coding to non-MPM indices based on specific criteria. When the non-MPM index satisfies certain conditions, a shorter code is used; otherwise, a longer code is used. This parameter-based coding approach reduces the overall bitstream size while maintaining manageable decoding complexity through predefined coding rules.
3Measurement precision
If the number of intra prediction modes is increased, then prediction accuracy is improved, but coding efficiency deteriorates
Solution Approach 1:
The patent segments the full set of intra prediction modes into MPM modes (most probable) and non-MPM modes. By deriving M > 3 MPMs and using selective coding based on mode probability, the system improves prediction accuracy for common cases while maintaining coding efficiency through conditional processing and optimized syntax element design.
Solution Approach 2:
The patent derives more than three MPMs (excessive action compared to conventional HEVC) to ensure that the most probable modes are adequately represented. This partial expansion of MPM coverage improves prediction accuracy without requiring full coding of all possible modes, thereby maintaining coding efficiency.
Data Source
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AI summary
A device includes one or more processors configured to derive M most probable modes (MPMs) for intra prediction of a block of video data. A syntax element that indicates whether a MPM index or a non-MPM index is used to indicate a selected intra prediction mode of the plurality of intra prediction modes for intra prediction of the block of video data is decoded. The one or more processors are configured such that, based on the MPM index indicating the selected intra prediction mode, the one or more processors decode the non-MPM index. The non-MPM index is encoded in the bitstream as a code word shorter than [log2 N] bits if the non-MPM index satisfies a criterion and is encoded in the bitstream as a fixed length code with [log2 N] bits otherwise. The one or more processors reconstruct the block based on the selected intra prediction mode.