Polynomial Color Gamut Mapping in Perceptual Space
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Solution Overview
Problem
Conventional color mapping techniques, such as linear or piecewise-linear projection in non-perceptual x-y chromaticity space, fail to accurately reproduce colors, especially memory colors, when mapping from one color gamut to another, leading to distorted and unrealistic images due to their restrictive nature and inability to preserve luminance relationships.
Innovation Solution
The use of three-dimensional perceptual color spaces that allow for non-linear polynomial mapping, specifically rubber-sheet polynomial mapping and a memory color look-up table, to maintain hue constancy and accurately map colors from one gamut to another, ensuring better calorimetric accuracy and preservation of memory colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If linear or piecewise-linear projection mapping is used in non-perceptual x-y chromaticity space, then the mapping process is simple and computationally efficient, but color accuracy deteriorates and memory colors are distorted
Solution Approach 1:
The patent transforms the mapping approach from linear projection in non-perceptual x-y chromaticity space to non-linear polynomial mapping in perceptual L*a*b* color space. This parameter change includes using polynomial equations with multiple terms (e.g., second-order or higher) to model the complex non-linear relationship between source and target color gamuts, thereby achieving accurate color reproduction including memory colors while maintaining computational feasibility through pre-computed polynomial coefficients.
2Ease of operation
If linear mapping is used to map color gamuts, then the mapping computation is straightforward, but calorimetric accuracy is lost and core colors are compressed
Solution Approach 1:
The patent introduces non-linearity into the mapping process by using polynomial equations that can model curved relationships between color values. Instead of straight-line (linear) mappings, the polynomial functions with multiple terms (e.g., a0 + a1*L_s + a2*a_s + a3*L_s*a_s + ...) capture the curved, non-linear transformations needed to preserve calorimetric accuracy and prevent compression of core colors while adapting to the target display's color gamut characteristics.
3Measurement precision
If the target display device uses its expanded color gamut fully, then color reproduction fidelity improves, but the mapping complexity increases
Solution Approach 1:
The patent performs preliminary characterization of the target display device's color gamut and pre-computes the polynomial mapping coefficients based on measured color data. By conducting this complex analysis and coefficient calculation in advance (before actual image rendering), the system enables full utilization of the display's expanded color gamut with accurate polynomial-based mappings, while the runtime complexity is reduced to evaluating pre-computed polynomial equations for each pixel.
Data Source
AI summary
Disclosed embodiments relate to techniques for color gamut mapping when an input signal transmitting color visual images has a different color gamut than does the output display device. Polynomial rubber-sheet mapping may be used to translate the input color gamut to the output color gamut on a hue-by-hue basis within a three-dimensional perceptual color space. Also, a memory color look-up table may be used to preserve memory colors in the input gamut which are capable of reproduction within the output gamut. By using such techniques alone or in combination, it may be possible to more effectively map an input color gamut to a different output color gamut with improved calorimetric accuracy.