Color Compression Apparatus for Hue Shift Prevention
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Solution Overview
Problem
Existing color compression methods fail to accurately reproduce colors across devices with different color gamuts, particularly causing hue shifts and improper gradation due to differences in lightness and hue values between monitors and printers.
Innovation Solution
A color compression apparatus and method that determines the hue and lightness of input color data, adjusts lightness based on target values to match the output device's gamut, and corrects chroma values to ensure proper gradation and color impression consistency across devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional color compression methods are used to convert colors between devices with different color gamuts, then color conversion is achieved, but hue shifts and improper gradation occur due to differences in lightness and hue values between devices
Solution Approach 1:
The patent transforms color data from device-dependent RGB/CMYK spaces to device-independent L*a*b* space, changing the parameter representation to separate lightness (L*) from chromaticity (a*, b*). This parameter transformation enables independent adjustment of lightness while preserving hue information, resolving the contradiction between color conversion and hue consistency.
Solution Approach 2:
The patent segments the color conversion process into distinct steps: hue determination from chromaticity coordinates, lightness adjustment based on target device characteristics, and chroma correction. This segmentation allows precise control over each aspect of color reproduction, preventing hue shifts while adapting to different device gamuts.
2Stability of the object's composition
If device-color values are kept equal across different devices, then color matching is attempted, but different hue values result in the uniform color space due to device characteristics
Solution Approach 1:
The patent introduces the L*a*b* color space as an intermediary between source and target devices. By converting to this device-independent space first, the system establishes a common reference frame where hue can be accurately determined and preserved during conversion, eliminating the problem of hue drift that occurs when directly mapping device-specific color values.
Solution Approach 2:
The patent implements feedback by determining hue from the input color data in L*a*b* space and using this hue information to guide the lightness adjustment process. The system continuously references the target device's full-color lightness characteristics to ensure the converted colors match the intended hue, correcting for device-specific variations.
3Device complexity
If equal hue lines are assumed to be linear in uniform color space, then simplification is achieved, but incorrect gradation reproduction results
Solution Approach 1:
The patent changes the approach from assuming linear equal-hue lines to calculating actual hue values from chromaticity coordinates (a*, b*) using the arctangent function. This parameter transformation reveals the true non-linear nature of equal-hue lines in L*a*b* space and enables accurate hue determination despite the curvature, resolving the contradiction between simplicity and accuracy.
Data Source
AI summary
According to a hue conversion, hue angles of C, M, and Y are always set to hue angles HC, HM, and HY of C, M, and Y of a printer, hue angles of R and G are always set to hue angles HR and HG of R and G of a monitor, and the hue angle of B is always set to a value HB desired by a user. The gradation from black through a full color to white is made linear in each color of R, G, B, C, M, and Y according to the hue conversion. The user sets the hue angle HB for B. Therefore, the user can obtain blue color B which provides the user's favorite hue and gradation. Every hue can be reproduced excellently and gradations can be reproduced without color shifts.