Chroma QP Mapping Signaling for Luma-Based Video Compression
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Solution Overview
Problem
Existing video coding technologies face challenges in achieving efficient compression of video data without sacrificing picture quality, particularly in scenarios with limited network resources and increasing demands for higher video quality.
Innovation Solution
A method for obtaining chrominance quantization parameters based on luminance quantization parameters using a chroma QP mapping table, which involves parsing a bitstream to derive chroma QP values through a piecewise mapping function, reducing signaling overhead by signaling only pivot points and their differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If chroma QP is derived using a chroma_qp_offset_cb/cr parameter, then the mapping function is simple and easy to implement, but the signaling overhead is reduced and compression efficiency is improved
Solution Approach 1:
The patent segments the chroma QP mapping into two independent parts: a simple offset parameter (cb_qp_offset, cr_qp_offset) that is easily signaled, and a lookup table (ChromaQpTable) that stores pre-computed mapping values. This segmentation allows the complex mapping function to be implemented through table lookup rather than complex calculations during decoding, reducing the complexity burden on the decoder while maintaining efficient compression.
Solution Approach 2:
The patent applies preliminary action by pre-computing and storing the ChromaQpTable during encoder operation. The table is filled by iterating through possible QP values and calculating corresponding chroma QPs using the mapping function, then storing these pre-computed pairs. This eliminates the need for complex real-time calculations during decoding, as the decoder only needs to perform simple table lookup operations.
2Productivity
If a complex chroma QP mapping function is used to improve compression efficiency, then picture quality is enhanced, but the signaling overhead increases
Solution Approach 1:
The patent extracts the complex mapping logic from the decoding process and places it in the encoding process. The ChromaQpTable is computed and stored during encoding, containing all the complex mapping relationships. During decoding, only simple table lookup operations are needed, significantly reducing the computational complexity and signaling requirements while maintaining the compression efficiency benefits of the complex mapping function.
Solution Approach 2:
The patent uses a lookup table (ChromaQpTable) as a copy of the complex mapping function. Instead of transmitting or computing the complex mapping function during decoding, the pre-computed mapping values are stored in the table and simply copied/retrieved during the decoding process. This copying approach maintains the compression efficiency while dramatically reducing the operational complexity at the decoder.
3Ease of manufacture
If chroma QP is always derived from luma QP using a fixed mapping, then implementation is simplified, but adaptability to different video content and quality requirements is reduced
Solution Approach 1:
The patent introduces dynamic adaptability through the ChromaQpTable that can be configured based on different video content characteristics and quality requirements. The table is populated using the mapping function with parameters like cb_qp_offset and cr_qp_offset that can be adjusted according to the specific needs of different video streams. This allows the system to adapt to various content types and quality requirements while maintaining a relatively simple implementation structure.
Solution Approach 2:
The patent enables parameter changes by allowing the cb_qp_offset and cr_qp_offset values to be adjusted based on different video content characteristics and quality requirements. These offset parameters are used to modify the chroma QP derivation process, enabling the system to adapt to different compression needs while maintaining the same basic lookup table structure. This provides flexibility without significantly complicating the implementation.
Data Source
AI summary
A method of obtaining a chrominance quantization parameter (QP) for chrominance components based on a luminance QP for a luminance component, wherein the method is performed by a decoder, and comprises parsing a received bitstream comprising a sequence parameter set (SPS) to obtain the luminance QP and information of a mapping function (f) which associates a QP index (QPi) to a chrominance QP (QPc), wherein the chroma QP mapping table is signaled in the SPS; obtaining the QPi based at least in part on the luminance QP; obtaining the mapping function based on the obtained information of the mapping function; and obtaining a QPc based on the obtained mapping function and the obtained QPi.