ICtCp Chroma Quantization for HDR Video Bitrate Reduction
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Solution Overview
Problem
Existing video compression standards, such as HEVC, are inefficient in encoding high-dynamic range (HDR) images in the ICtCp color format, leading to increased bitrates due to higher energy in chroma components, which is not effectively addressed by current chroma quantization and mode decision methods.
Innovation Solution
Optimizing chroma quantization by adjusting chroma QP offset parameters and improving chroma mode decision by computing saturation and hue values, while maintaining constant luminance through chroma gamut mapping and adjustment, to reduce bitrates and improve coding efficiency in the ICtCp color format.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If existing video compression standards (HEVC) are used to encode HDR images in ICtCp color format, then coding efficiency is maintained for standard dynamic range content, but chroma bitrates increase due to higher energy in chroma components
Solution Approach 1:
The patent modifies chroma quantization parameters (QP offsets) specifically for ICtCp color format encoding. By adjusting CbQpOffset and CrQpOffset based on the relationship between capture and encoded color spaces, the patent reduces chroma component energy and bitrate while maintaining perceptual quality for HDR content.
Solution Approach 2:
The patent applies different chroma QP offset adjustments depending on the specific color space relationship. When capture and encoded color spaces match, no offset is applied; when capture is a subset of encoded, a scaling factor greater than 1 is used. This localized parameter adjustment optimizes chroma compression for ICtCp specifically without affecting other color formats.
2Productivity
If chroma QP offset parameters are adjusted to reduce chroma bitrates, then coding efficiency improves, but color accuracy may deteriorate
Solution Approach 1:
The patent incorporates a feedback mechanism by computing the relationship between capture color space and encoded color space, then using this information to determine appropriate chroma QP offsets. The scaling factor is derived based on color space differences, ensuring that compression adjustments are proportional to the actual color space transformation requirements.
Solution Approach 2:
The patent dynamically adjusts chroma QP parameters based on the color space relationship. By scaling the chroma QP offset according to the ratio of color space gamuts, the patent maintains color accuracy while optimizing compression. The adjustment is proportional to the color space difference, preserving color fidelity.
3Quantity of substance
If chroma subsampling is applied to reduce data amount, then bandwidth requirements decrease, but luminance-chroma separation quality may worsen
Solution Approach 1:
The patent optimizes chroma quantization parameters to work effectively with chroma subsampling in ICtCp color format. By adjusting CbQpOffset and CrQpOffset, the patent ensures that subsampled chroma components maintain adequate quality while achieving the desired data reduction for efficient transmission and storage.
Data Source
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AI summary
Methods to improve the quality of coding high-dynamic range (HDR) signals in the ICtCp color space are presented. Techniques are described to a) generate optimum chroma Offset and scaling parameters, b) compute chroma mode decisions by optimizing mode selection distortion metrics based on chroma saturation and hue angle values, and c) preserving iso-luminance by maintaining in-gamut values during chroma down-sampling and chroma up-sampling operations.