HEVC Chroma Intra Mode Codeword Assignment Optimization
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Solution Overview
Problem
The existing binarization/Variable Length Coding (VLC) scheme in Advanced Video Coding (AVC) is inefficient due to the high probability of the 'same as luma' mode being used for chroma components, which is encoded using the longest codeword, and redundancy between modes, leading to decreased coding efficiency.
Innovation Solution
A modified codeword assignment scheme for HEVC, where the 'same as luma' mode is assigned the fewest bits, and if it is the same as another mode, the codeword assignment is reconfigured to remove the 'same as luma' mode and reduce bits in remaining modes, optimizing the truncated unary code from 0 through 4 to 0 through 3.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the standard VLC codeword assignment scheme is used for chroma intra mode signaling, then the coding structure is simple and easy to implement, but the coding efficiency is decreased because the 'same as luma' mode (which occurs with high probability) is assigned the longest codeword
Solution Approach 1:
The patent inverts the conventional VLC codeword assignment by assigning the shortest codeword (1 bit) to the 'same as luma' mode instead of the longest codeword. This inversion directly addresses the contradiction by making the most frequently occurring mode the most efficiently encoded, thereby improving coding efficiency without significantly increasing complexity
Solution Approach 2:
The patent changes the codeword length parameter for different chroma intra prediction modes based on their probability of occurrence. By assigning shorter codewords to more probable modes (especially 'same as luma') and longer codewords to less probable modes, the patent optimizes the average codeword length and improves coding efficiency
2Productivity
If all 5 chroma intra prediction modes are encoded with distinct codewords, then the prediction accuracy is maintained, but redundancy exists between modes leading to inefficient bit usage
Solution Approach 1:
The patent merges the encoding of multiple chroma intra prediction modes into a unified structure where the luma prediction mode information is reused for chroma prediction. By combining the encoding of 'same as luma' with the luma mode signaling, the patent eliminates redundancy and improves bit usage efficiency while maintaining prediction accuracy
Solution Approach 2:
The patent makes the luma prediction mode signaling serve a dual function: it directly indicates the chroma prediction mode when they are the same, and provides the basis for deriving chroma prediction when modes differ. This multi-functionality reduces the need for separate explicit chroma mode signaling, improving efficiency
Data Source
AI summary
Intra prediction is used in state-of-the-art video coding standards such as AVC. The intra prediction modes are coded into the bitstream. Luma and chroma components could potentially have different prediction modes. For chroma components, there are 5 different modes defined in AVC: vertical, horizontal, DC, diagonal down right, and “same as luma”. Statistics show that the “same as luma” mode is frequent used, but in AVC, this mode is encoded using more bits than other modes during entropy coding, therefore the coding efficiency is decreased. Accordingly, a modified binarization/codeword assignment for chroma intra mode signaling is able to be utilized for high efficiency video coding (HEVC), the next generation video coding standard.