Adaptive Loop Filter Coefficient Coding With Shorter Codewords
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Solution Overview
Problem
The existing video coding standards, such as HEVC, face challenges in efficiently encoding and decoding adaptive loop filter (ALF) coefficients due to filter position-dependent entropy coding and large worst-case codeword lengths, which are difficult for processors to handle, especially for 32- and 64-bit systems.
Innovation Solution
Implementing coefficient position-independent and dependent entropy coding techniques, including exp-Golomb codes and fixed length codes, to reduce the worst-case codeword lengths and improve the efficiency of ALF coefficient encoding and decoding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If filter position-dependent entropy coding is used for ALF coefficients, then coding efficiency is improved, but worst-case codeword lengths become large and processing complexity increases
Solution Approach 1:
The patent changes the coding parameters by introducing a threshold value for ALF coefficient magnitude. Coefficients below the threshold are encoded using a first code with shorter codewords, while coefficients at or above the threshold use a second code with longer codewords. This parameter-based differentiation resolves the contradiction by limiting worst-case codeword lengths while maintaining coding efficiency for most coefficients.
Solution Approach 2:
The patent implements dynamic coding strategy where the encoding method adapts based on the coefficient value and its position. The system dynamically selects between different code types (first code for small coefficients, second code for large coefficients) based on real-time conditions, optimizing the balance between coding efficiency and processing complexity.
2Productivity
If filter position-dependent entropy coding is used for ALF coefficients, then coding efficiency is improved, but bit rate increases
Solution Approach 1:
The patent introduces a magnitude threshold parameter that divides coefficients into two groups. By using shorter codewords for coefficients below the threshold and longer codewords only when necessary, the system optimizes the average bit rate while maintaining coding efficiency, preventing unnecessary bit rate increase.
Solution Approach 2:
The patent applies partial coding action by using simplified first codes for the majority of coefficients (those below threshold) and only applying more complex second codes when necessary. This partial application of comprehensive coding reduces overall bit rate while maintaining efficiency where needed.
3Device complexity
If conventional entropy coding is used for ALF coefficients, then processing is simplified, but coding efficiency deteriorates
Solution Approach 1:
The patent segments the ALF coefficients into different categories based on their magnitude relative to a threshold. This segmentation allows the system to apply different coding methods to different segments, achieving both processing simplicity for most coefficients and coding efficiency where needed.
Solution Approach 2:
The patent applies local quality by treating different coefficient regions differently. Coefficients with magnitude below the threshold receive simplified processing with first codes, while coefficients at or above the threshold receive enhanced processing with second codes. This localized differentiation optimizes both simplicity and efficiency.
Data Source
AI summary
A method for adaptive loop filtering is provided that includes determining a coefficient value for each coefficient position of an adaptive loop filter, applying the adaptive loop filter to at least a portion of a reconstructed picture using the coefficient values, and entropy encoding coefficient values into a compressed bit stream using predetermined short binary codes, wherein the short binary code used depends on the coefficient position of the coefficient value.