Transform-Skipped Block Context Modeling for HEVC Compression
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Solution Overview
Problem
In High Efficiency Video Coding (HEVC), the encoding and decoding of transform skipped blocks are inefficient due to incorrect context probabilities, which disrupt the adaptive context model used for conventional transform blocks, leading to increased bit usage and compromised encoding/decoding performance.
Innovation Solution
Adapting the context model for transform skipped blocks by starting in a different state, similar to that used for transformed blocks, to improve the derivation of contexts for nonzero residual values and coefficients, allowing the reuse of the existing context model without introducing new complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the existing context model is used for transform skipped blocks without modification, then the implementation complexity is low, but the compression efficiency deteriorates due to incorrect context probabilities
Solution Approach 1:
The patent applies different starting states of the context model based on the block type (transform skipped vs. conventional transform blocks). This local differentiation allows the context probabilities to be appropriately adapted to the specific characteristics of transform skipped blocks, improving compression efficiency without requiring a completely new context model implementation.
Solution Approach 2:
The patent modifies the starting state parameter of the existing context model based on the block type. By changing this single parameter (starting state) rather than the entire context model structure, the system achieves improved compression efficiency for transform skipped blocks while maintaining low implementation complexity.
2Loss of energy
If the context model is adapted for transform skipped blocks by starting in a different state, then the compression efficiency is improved, but the device complexity increases
Solution Approach 1:
The adaptation is applied locally only to transform skipped blocks by changing the starting state, rather than modifying the entire context model structure. This localized approach improves compression efficiency for the specific block type while minimizing the increase in overall system complexity.
Solution Approach 2:
The patent changes only the starting state parameter of the context model based on block type, rather than redesigning the entire context model. This parameter-based adaptation achieves improved compression efficiency with minimal complexity overhead.
3Ease of operation
If transform skipped blocks use the same context model starting state as conventional blocks, then the implementation is simpler, but the encoding performance is compromised due to disrupted adaptive context model
Solution Approach 1:
The patent applies a differentiated starting state specifically for transform skipped blocks while maintaining the original starting state for conventional blocks. This local differentiation preserves the adaptive context model's effectiveness for each block type, improving encoding performance without significantly complicating the overall implementation.
Solution Approach 2:
The patent makes the context model starting state dynamic, selecting different starting states based on the block type. This dynamic adaptation allows the context model to better match the statistical characteristics of different block types, improving encoding performance while maintaining implementation feasibility through conditional logic.
Data Source
AI summary
Video encoder and decoder and methods therein for transform skipped encoding and decoding of blocks of pixels. The methods comprise a modified use of an existing context model associated with transform coefficients, for deriving contexts for a bitmask indicating which residual values (i.e., not transform coefficients), in a transform skipped residual block, that are greater than one. The methods are applicable to video coding schemes such as HEVC.