Chroma Quantization Parameter Mapping for Video Color Preservation
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Solution Overview
Problem
In video coding, strong quantization can lead to the complete loss of chroma information, particularly at high quantization parameter (QP) values, resulting in loss of color in decoded video due to excessive attenuation of chroma quantizer step sizes.
Innovation Solution
A method is introduced where the chroma quantization parameter (QPc) is derived based on the luminance QP using a preset lookup table with a maximum difference of 3, employing a monotonically increasing mapping function to reduce QP attenuation for chroma components, and optionally adjusting the chrominance QP by adding an offset or clipping the QP index within a specific range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If strong quantization is applied to reduce data size, then compression ratio is improved, but chroma information is completely quantized to zero resulting in loss of color
Solution Approach 1:
The patent changes the quantization parameter relationship between luma and chroma components. Instead of using equal QP values, it introduces a mapping function that derives chroma QP from luma QP with a maximum difference of 3, preventing chroma QP from becoming too large and causing complete quantization to zero while still achieving compression
2Manufacturing precision
If chroma quantizer step sizes are heavily attenuated to preserve color, then chroma quality is improved, but overall compression efficiency decreases
Solution Approach 1:
The patent optimizes the chroma quantizer step sizes by establishing a controlled relationship with luma QP. The mapping function ensures chroma QP does not exceed luma QP by more than 3, maintaining chroma quality while allowing sufficient quantization for compression efficiency
Solution Approach 2:
The patent uses the luma quantization parameter as a reference to derive chroma QP through a mapping function. This copying approach with controlled deviation (max difference of 3) ensures chroma quality matches luma quality closely while maintaining compression efficiency
Data Source
AI summary
A method of obtaining quantization parameter (QP) for chrominance components based on QP for luminance component, wherein the method is performed by a decoder or encoder, and wherein the method comprises obtaining a luminance QP for a luma component of a coding unit; obtaining a QP index (QPi) based at least in a part on the luminance QP; and obtaining a chrominance QP (QPc) for a chroma component of the coding unit based on the QP index by using a preset lookup table, wherein the maximum difference between the QP index and the chrominance QP is equal to 3.