Sub-block Transform Skip Mode for Lossless Video Coding
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Solution Overview
Problem
Current video coding standards face challenges in efficiently compressing digital video due to high bandwidth demands and the need for improved coding efficiency, particularly in representing video blocks without applying transforms or quantization processes.
Innovation Solution
The method involves determining the applicability of modes that skip transform and quantization processes for video blocks, enabling transquant bypass mode, and disabling processes like luma mapping with chroma scaling, to perform conversions between video blocks and bitstream representations, adhering to specific format rules that govern the inclusion and order of syntax elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If transform and quantization processes are applied to video blocks, then compression performance is improved, but computational overhead increases
Solution Approach 1:
The video block is divided into multiple sub-blocks, and the transform skip mode is applied selectively at the sub-block level rather than uniformly across the entire block. This segmentation allows different processing approaches for different regions, reducing overall computational overhead while maintaining compression performance in areas where transforms are still applied.
Solution Approach 2:
Instead of applying transform and quantization processes to the entire video block, the patent applies these processes only to specific sub-blocks where they are most beneficial. The transform skip mode is selectively disabled for certain sub-blocks based on local characteristics, performing partial action rather than exhaustive processing across all blocks.
2Productivity
If transform skip mode is applied at the block level, then computational overhead is reduced, but coding efficiency deteriorates due to inability to adapt to local variations
Solution Approach 1:
The patent segments the video block into multiple sub-blocks and enables independent control of transform skip mode for each sub-block. This fine-grained segmentation allows the encoder to adapt to local variations in image content, improving coding efficiency by applying transforms only where necessary while avoiding them in regions where they would be detrimental.
Solution Approach 2:
The transform skip mode is controlled locally at the sub-block level rather than globally for the entire block. Each sub-block can have its own transform skip flag, allowing the coding strategy to be optimized for local characteristics such as edge directions, texture patterns, and frequency content, thereby improving overall coding efficiency.
3Manufacturing precision
If luma mapping with chroma scaling (LMCS) process is enabled, then color accuracy is improved, but processing complexity increases for lossless coding
Solution Approach 1:
The patent extracts or removes the LMCS process from the coding pipeline when operating in lossless mode with transform skip. By taking out this complex color space transformation process, the implementation achieves lossless coding without the additional processing complexity introduced by LMCS, while still maintaining color accuracy through alternative methods.
Solution Approach 2:
The LMCS process is applied selectively rather than universally. The patent disables LMCS for specific sub-blocks or coding units where it would add unnecessary complexity, particularly in lossless coding scenarios where transform skip is already applied. This partial application reduces overall processing complexity while maintaining color accuracy where LMCS provides benefit.
Data Source
AI summary
Devices, systems and methods for lossless coding for visual media coding are described. An exemplary method for video processing includes determining, at a sub-block level of a current video block comprising multiple sub-blocks, whether a coding mode is enabled for representing a corresponding sub-block in a bitstream representation, where, for a given sub-block with the coding mode enabled, the given sub-block is represented in the coded representation without applying a forward transform or the given sub-block is reconstructed from the coded representation without applying an inverse transform, and performing, based on the determining, a conversion between the current video block of a video and the bitstream representation of the video.