Entropy Coding of Transform Coefficients With Single-Pass Flags
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Solution Overview
Problem
Current entropy coding methods, such as CABAC, are inefficient for larger block sizes due to the need for two scanning passes and excessive use of binary arithmetic coding operations, particularly in video coding systems.
Innovation Solution
A systematic entropy coding approach that uses a binary arithmetic coding engine with reduced binary bins, employing flags like last_ge2_flag and last_flag to indicate non-zero coefficients, allowing for single-pass coding of coefficient blocks and reducing binary bins, thereby simplifying the coding system and enhancing compression efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CABAC is used for entropy coding of quantized transform coefficients, then coding efficiency is improved, but two scanning passes are required and device complexity increases
Solution Approach 1:
The patent segments the coding process by introducing a significance map pass that separates coefficient significance detection from value coding. The significance map is coded first in a forward scan, then value coding is performed in a separate pass using the pre-computed significance map, dividing the complex CABAC process into manageable segments.
Solution Approach 2:
The patent performs preliminary action by computing and coding the significance map before value coding. The significance map indicates which coefficients are non-zero, allowing the decoder to prepare for efficient value decoding by knowing the positions and significance of non-zero coefficients in advance.
2Productivity
If CABAC is used for entropy coding, then compression efficiency is improved, but excessive binary arithmetic coding operations are performed
Solution Approach 1:
The patent extracts the significance information from the full coefficient data and codes it separately in the significance map pass. By taking out the significance map coding from the main value coding process, the patent reduces the number of binary arithmetic coding operations required during value decoding, as the decoder already knows which positions contain non-zero values.
Solution Approach 2:
The patent changes the coding parameter strategy by using context-adaptive binary arithmetic coding selectively - applying it to the significance map in the first pass and then using simpler decoding based on the pre-computed significance map in the second pass, rather than applying full CABAC operations to all coefficients.
3Measurement precision
If CABAC is designed for smaller block sizes, then coding precision is maintained, but efficiency decreases for larger blocks
Solution Approach 1:
The patent creates a universal significance map coding approach that works efficiently for both small and large block sizes. The significance map structure and coding method remain the same regardless of block size, making the system multi-functional and adaptable to different block dimensions without sacrificing precision or efficiency.
Data Source
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AI summary
Methods and apparatus are provided for improved entropy encoding and decoding. An apparatus includes a video encoder (200) for encoding at least a block in a picture by transforming a residue of the block to obtain transform coefficients, quantizing the transform coefficients to obtain quantized transform coefficients, and entropy coding the quantized transform coefficients. The quantized transform coefficients are encoded using a flag to indicate that a current one of the quantized transform coefficients being processed is a last non-zero coefficient for the block having a value greater than or equal to a specified value.