Color Conversion Table Tone Discontinuity Correction
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Solution Overview
Problem
Existing color conversion technologies using 3D-LUTs in electrophotographic apparatuses often result in tone discontinuity, leading to pseudo contours in images with smooth tone changes, which can be mitigated but at the cost of color reproducibility.
Innovation Solution
A method that extracts and corrects high-frequency components of image data in the color conversion process, specifically addressing tone discontinuity by modifying the 3D-LUT to prevent pseudo contours while maintaining color reproducibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If smoothing processing is performed on output signal values in the 3D-LUT, then pseudo contours are reduced, but color reproducibility is significantly changed
Solution Approach 1:
The patent segments the color conversion process into two distinct stages: a first color conversion process that handles color space transformation without smoothing, and a second color conversion process that applies smoothing only to specific output signal values. This segmentation allows the system to reduce pseudo contours in gradient areas while preserving color reproducibility for pure color regions, thereby resolving the technical contradiction between reducing harmful artifacts and maintaining color accuracy.
2Stability of the object's composition
If smoothing processing is strengthened to reduce pseudo contours, then tone discontinuity is reduced, but color reproducibility deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different regions in the color conversion table. Specifically, smoothing processing is applied selectively based on the gradient magnitude of output signal values - strong smoothing is applied only to regions with small gradients where pseudo contours are likely to occur, while regions with large gradients (pure colors) are preserved without smoothing. This localized approach maintains tone continuity in gradient areas while preserving color reproducibility overall.
3Adaptability or versatility
If color conversion is performed using 3D-LUT with individually defined output signal values, then color space conversion is achieved, but tone discontinuity occurs between contiguous data
Solution Approach 1:
The patent employs preliminary action by pre-calculating and storing smoothing correction values in the color conversion table before actual image conversion occurs. The system identifies regions prone to tone discontinuity based on gradient analysis and pre-applies appropriate smoothing coefficients to those specific entries in the 3D-LUT. When color conversion is performed, these pre-smoothed values are directly used, ensuring tone continuity is maintained while preserving the adaptability of the color space conversion process.
Data Source
AI summary
An information processing apparatus that generates a color conversion table to be set in an image forming apparatus includes a conversion unit that uses a color conversion table to convert input RGB values into output RGB values, wherein the color conversion table is a conversion table for conversion of the input RGB values into output RGB values that depend on a color gamut of the image forming apparatus, an extraction unit that extracts an L value indicating lightness out of a plurality of elements forming Lab values corresponding to the output RGB values, a correction unit that corrects the extracted L value, and a correction unit that uses the corrected L value, and a and b values indicating chromaticity and other than the extracted L value out of the plurality of elements forming the Lab values corresponding to the output RGB values to correct the color conversion table.