Entropy Coding of Transform Coefficients in a Single Scan
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current entropy coding methods, such as CABAC, are inefficient for larger block sizes in video coding due to the need for two scanning passes and lack of systematic implementation, leading to increased complexity and reduced compression efficiency.
Innovation Solution
A systematic entropy coding approach that uses a flag to indicate the last non-zero coefficient in a block, allowing for encoding and decoding in a single scanning pass, reducing binary bins and improving compression efficiency by eliminating unnecessary binary arithmetic coding operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CABAC coding is used for quantized transform coefficients, then coding efficiency is improved, but device complexity increases due to two scanning passes
Solution Approach 1:
The patent segments the coding process by separating significance map coding from level coding, but then recombines them in a unified single-pass systematic approach. The coefficient block is divided into regions based on the last non-zero coefficient position, allowing different coding strategies for different regions while maintaining single-pass operation.
Solution Approach 2:
Instead of using the traditional two-pass approach (forward zigzag for significance, inverse zigzag for levels), the patent inverts the methodology by performing both significance and level coding in a single forward pass, using systematic arithmetic coding throughout rather than separating the passes.
2Productivity
If CABAC coding is used for smaller block sizes, then coding efficiency is improved, but it becomes less efficient for larger block sizes
Solution Approach 1:
The patent changes the fundamental parameters of the coding approach by transitioning from context-based adaptive binary arithmetic coding to systematic arithmetic coding with a unified probability model. This parameter change makes the coding method scaleable to different block sizes without the performance degradation seen in CABAC for large blocks.
Solution Approach 2:
The systematic arithmetic coding approach described in the patent is universally applicable to block sizes of all dimensions. The same coding procedure and probability models work efficiently for both small and large blocks, providing multi-functional capability that CABAC lacks.
3Measurement precision
If two scanning passes are performed for CABAC coding, then significance map and non-zero values are coded separately, but loss of time increases due to multiple passes
Solution Approach 1:
The patent merges the significance map coding and level coding into a single unified process. Both operations are performed in one forward scanning pass, eliminating the time loss associated with performing separate passes while maintaining the precision needed for accurate coefficient representation.
Solution Approach 2:
The patent performs preliminary identification of the last non-zero coefficient position during the single forward pass, which allows subsequent levels to be coded immediately without requiring a separate backward pass. This preliminary action within the single pass eliminates the time penalty of multiple scans.
Data Source
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.