Chroma Adjustment for HDR Video Compression Efficiency
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Solution Overview
Problem
Video coding technologies face challenges in reducing artifacts and improving compression efficiency due to the use of non-constant luminance and highly nonlinear transfer functions, particularly in representing chroma values, which leads to inefficiencies in encoding and decoding processes.
Innovation Solution
A method for processing pixels that involves obtaining lower and upper limits for color components based on distances in a second color space, allowing for filtered values that are within these limits to replace original values, thereby reducing artifacts and improving encoding efficiency without being visible to the human visual system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If luma adjustment is applied to correct luminance values, then luminance accuracy is improved, but chroma variation increases leading to higher bit rate requirements
Solution Approach 1:
The patent applies chroma adjustment before luma adjustment in the encoding process. By pre-adjusting chroma values to be more representative of the actual luminance contribution, the subsequent luma adjustment requires smaller corrections, reducing the variance in corrected luma values and lowering bit rate requirements while maintaining luminance accuracy.
Solution Approach 2:
The patent modifies chroma parameter values (Cb and Cr) to better represent their actual contribution to luminance. This parameter change makes the chroma signal more predictable and less variable after luma correction, reducing the bit rate needed to encode the corrected luma values while preserving luminance precision.
2Productivity
If non-constant luminance YCbCr representation is used, then compression efficiency is improved, but severe artifacts appear in saturated colors
Solution Approach 1:
The patent changes the chroma parameter values to be more representative of actual luminance contribution. This parameter modification reduces the discrepancy between encoded and actual colors in saturated regions, eliminating artifacts while preserving the compression efficiency benefits of YCbCr representation.
Solution Approach 2:
The patent replaces the conventional luma adjustment-only approach with a combined chroma adjustment and luma adjustment process. This substitution of the correction mechanism addresses the root cause of artifacts in saturated colors while maintaining compression efficiency.
3Manufacturing precision
If highly nonlinear transfer functions are used for encoding, then dynamic range representation is improved, but encoding complexity increases
Solution Approach 1:
The patent applies chroma adjustment before the nonlinear transfer function encoding. This preliminary adjustment simplifies the subsequent encoding process by pre-correcting chroma values, reducing the computational complexity of handling highly nonlinear transfer functions while preserving dynamic range representation accuracy.
4Productivity
If chroma values are adjusted to be more representative, then compression efficiency is improved, but color accuracy may be compromised
Solution Approach 1:
The patent modifies chroma parameters to better represent luminance contribution, which improves compression efficiency. The modification is carefully controlled to maintain color accuracy by ensuring that the adjusted chroma values still accurately represent the intended color information while reducing variance.
Data Source
AI summary
A processing for a first pixel in a picture comprises obtaining a lower limit of a first color component of the first pixel in a first color space based on a distance between a color of the first pixel and a first distorted version of the color in a second color space. An upper limit of the first color component in the first color 5 space is obtained based on a distance between the color and a second distorted version of the color in the second color space. A filtered value is obtained of the first color component and which is equal to or larger than the lower limit and equal to or lower than the upper limit. The processing results in filtered values that are cheaper to encode but that are visibly undistinguishable from the original colors of the pixels.