Sign Coding for Transform Skipped Video Blocks
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Solution Overview
Problem
In video coding, transform skipping disrupts the assumptions underlying sign bit coding, leading to a bias in sign bits within individual blocks, which affects compression efficiency, as existing methods do not adapt the coding process effectively for blocks with skipped transforms.
Innovation Solution
The introduction of a same-sign flag to indicate when all non-zero coefficients in a block have a common sign, allowing for context-based encoding and reducing the need to encode individual sign bits, along with the use of finite state machines and sign flipping to improve context-based encoding, adapts the sign coding process for transform skipping blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If transform skipping is used in video coding, then computational complexity is reduced, but sign bit coding efficiency deteriorates due to bias in sign bits
Solution Approach 1:
The patent applies dynamics by making the sign bit coding process adaptive based on the actual sign distribution in transform-skipped blocks. A finite state machine tracks the sign bit sequence and dynamically adjusts coding strategy: when consecutive identical signs are detected, context-based coding is used to exploit the bias; when signs alternate frequently, non-context-based coding is used. This dynamic adaptation resolves the contradiction by optimizing sign bit coding efficiency for each specific block pattern while maintaining the low complexity of transform skipping.
Solution Approach 2:
The patent changes the coding parameter (coding method) based on the observed sign bit pattern. By monitoring the sign bit sequence and identifying patterns such as consecutive identical signs or alternating signs, the system switches between context-based coding and non-context-based coding. This parameter change allows the system to adapt to the specific characteristics of transform-skipped blocks, improving sign bit coding efficiency without adding significant computational complexity.
2Loss of information
If context-based encoding is applied to sign bits, then compression efficiency improves, but device complexity increases due to additional state tracking
Solution Approach 1:
The patent applies partial action by selectively using context-based encoding only when it is beneficial. The finite state machine monitors sign bit patterns and activates context-based coding only when consecutive identical signs are detected (indicating a pattern worth exploiting). When signs alternate frequently or show no pattern, the system reverts to simpler non-context-based coding. This partial application of context-based encoding improves compression efficiency for suitable cases while avoiding the overhead of maintaining complex state tracking for all blocks.
Solution Approach 2:
The system uses the inherent pattern in the sign bit sequence itself to determine whether context-based encoding is appropriate. The finite state machine is driven entirely by the sign bit data being coded, using the data's own characteristics to guide the coding strategy. This self-service approach allows the system to adapt to local patterns without requiring external control or complex pre-computed models, achieving good compression efficiency with minimal additional device complexity.
Data Source
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AI summary
Methods of encoding and decoding sign information for non-zero coefficients in a block of video with transform skipped. The methods include context-based coding of a flag that signals if all signs are the same in the block; using a finite state machine to determine contexts for coding of sign information, some of which may be context-based coded and some of which may be non-context-based coded; context-based coding of sign information wherein the context is based upon the signs of neighbouring coefficients; context-based coding of sign information, where the sign information is a prediction of the sign; and using a dedicated context to code signs with a sign flag indicating whether signs in a transform skipping block have been inverted to preserve a dominant sign bias.