3D LUT Coding for Color Gamut Scalability
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Solution Overview
Problem
The significant signaling overhead of 3D Look-Up Tables (LUTs) in color grading processes for scalable video coding leads to sub-optimal color gamut conversion and degradation of enhancement layer coding efficiency, particularly due to large table sizes and the need for sequence-level signaling.
Innovation Solution
The use of non-uniform octants for color space segmentation and hierarchical tree structured 3D data organization in an octree, allowing for lossy coding with reduced precision and coarser octants to reduce the number of entries in the 3D LUT table, along with recursive layer-first traversal for encoding vertices in the LUT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a full-resolution 3D LUT is used for accurate color gamut conversion, then color accuracy is improved, but signaling overhead increases significantly
Solution Approach 1:
The 3D LUT is segmented into multiple octants (typically 8 octants) that partition the color space. Each octant contains a subset of the total LUT entries, allowing selective transmission of only necessary octant data. This segmentation reduces the amount of data that needs to be signaled while maintaining color accuracy in relevant regions.
Solution Approach 2:
Different octants can be encoded with different precision levels based on their importance. Octants containing critical color information (such as skin tones or prominent colors in the scene) are encoded with higher precision, while less important octants use reduced precision. This local quality approach maintains overall color accuracy while reducing total signaling overhead.
2Loss of information
If 3D LUT is signaled at sequence level to reduce overhead, then signaling overhead is reduced, but color gamut conversion quality degrades
Solution Approach 1:
The patent enables dynamic selection of LUT signaling granularity between sequence-level and picture-level based on content requirements. The system can adaptively choose to signal only specific octants at sequence level when content is uniform, or switch to finer-grained picture-level signaling when color accuracy is critical, thus balancing overhead and quality dynamically.
Solution Approach 2:
The patent introduces parameters to control the precision and granularity of LUT signaling (such as octant selection flags and precision indicators). By changing these parameters, the system can adjust the trade-off between signaling overhead and color conversion quality, allowing flexible adaptation to different content types and quality requirements.
3Ease of manufacture
If uniform octants are used for 3D LUT partitioning, then implementation is simpler, but coding efficiency is reduced
Solution Approach 1:
The patent employs non-uniform octant partitioning where different octants can have different sizes or resolutions based on their importance. This asymmetric approach allows the system to allocate more bits to critical color regions and fewer bits to less important regions, improving coding efficiency while maintaining manageable implementation complexity through structured partitioning rules.
Data Source
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AI summary
Systems and methods for improving efficiency in three-dimensional (3D) look-up table (LUT) coding and/or reducing table size of a 3D LUT may be provided. For example, octants associated with the 3D LUT may be provided for color space segmentation and coding may be performed on an octree associated with the octants where coding may include encoding nodes of the octree associated with the octants and corresponding vertices of the 3D LUT belonging to the nodes. Conversion parameters represented by the nodes are lossy coded with reduced precision. The 3D LUT may also be signaled (e.g., based on a sequence and/or picture level).