Adaptive Residual Colour Transform Signaling for Video Coding
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Solution Overview
Problem
The Adaptive Residual Colour Transform (RCT) tool in HEVC is not effective for all prediction-based coding modes and incurs high computational costs at both the encoder and decoder sides, particularly due to the complexity of determining the cu_residual_act_flag and increased decoding complexity.
Innovation Solution
A method where a single RCT flag is signaled in the bitstream at a level higher than the Coding Unit (CU) level, simplifying the process at both the encoder and decoder by associating the flag with multiple CUs, and determining the application of RCT based on the best current coding mode, thereby reducing the need for evaluation loops and bitstream bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If Adaptive Residual Colour Transform is applied at Coding Unit level with per-CU flags, then coding precision is improved, but device complexity and computational cost increase significantly
Solution Approach 1:
The patent segments the video sequence into different coding modes (INTRA, INTER, IBC) and applies RCT selectively to specific segments (INTRA and IBC modes) while excluding others (INTER mode), thereby reducing overall complexity while maintaining precision where beneficial
Solution Approach 2:
Instead of applying RCT universally to all coding units, the patent applies it partially only to specific coding modes where it provides benefit, avoiding the excessive computational cost of universal application while maintaining adequate precision
2Adaptability or versatility
If RCT flag is signaled at CU level for each coding unit, then adaptability is improved, but loss of information increases due to additional bitstream overhead
Solution Approach 1:
The patent segments the adaptability control into mode-specific flags (intra_RCT_flag, ibc_RCT_flag) rather than per-CU flags, reducing bitstream overhead while maintaining adaptability to different coding modes
Solution Approach 2:
The patent applies adaptability partially by using a single flag structure that covers multiple CUs of the same mode, rather than full per-CU adaptability, thereby reducing bitstream overhead while maintaining sufficient versatility
3Manufacturing precision
If RCT is applied to all coding modes, then manufacturing precision is improved, but productivity decreases due to increased evaluation loops
Solution Approach 1:
The patent segments the application of RCT by mode type, applying it only to INTRA and IBC modes while skipping INTER mode, thereby reducing the number of evaluation loops and improving encoding speed while maintaining precision where needed
Solution Approach 2:
The patent applies RCT partially to only those coding modes where it provides benefit, avoiding the productivity loss that would result from evaluating and applying RCT to all modes including INTER where it is ineffective
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies the encoding and decoding processes, reduces computational complexity, and minimizes bitstream size by eliminating the need for parsing RCT flags at the CU level, while maintaining compatibility with existing HEVC versions.
Implementation Method 1
the residual colour transform converting colour pixel components of the residual block from a colour space to another colour space
Data Source
AI summary
The present invention is related to video coding and decoding, in particular HEVC RExt that define the adaptive residual color transform, Adaptive RCT, of a residue of pixels. Compared to HEVC RExt where Adaptive RCT is signalled at Coding Unit level, embodiments of the invention propose to signal it in the bitstream in association with two or more coding units forming the image. In other words, it is signalled at a level higher than the CU level, for instance at sequence or frame or slice or tile or coding tree block level. In addition, various flags at this higher level make it possible to generically define the applying or not of RCT for various respective coding modes, for instance Inter coding mode, Intra Block Copy coding mode or Intra coding mode where Chroma and Luma modes are the same. Such approach makes it possible to reduce the amount of evaluations to be performed.