Image Formation Control Using Histogram Equalization for False Contour Suppression
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Solution Overview
Problem
Existing image formation technologies face challenges in reproducing images with high visibility and gradation characteristics due to the limitations of subtractive color mixing, which can result in false contours and deterioration of color tones during gamut mapping.
Innovation Solution
An image formation control apparatus and method that performs color conversion using histogram equalization processing to adjust brightness gradation values, generating a visibility improvement color table for converting input image data into color material gradation data suitable for CMYK color materials, thereby enhancing image visibility and gradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If gamut mapping compresses color space using geometric rules, then color reproduction is improved, but false contours and gradation deterioration occur
Solution Approach 1:
The patent applies histogram equalization processing to transform the luminance distribution in the Lch color space, changing the statistical parameters of brightness gradation values. This transforms concentrated luminance values into evenly distributed ones, improving gradation characteristics while maintaining color accuracy. The method modifies the luminance parameter L through cumulative distribution function calculations, effectively suppressing false contours without compromising color reproduction.
Solution Approach 2:
The patent introduces the Lch color space as an intermediary between the input color space and the output CMYK color space. By performing histogram equalization in this intermediate Lch space before final color conversion, the method mediates between preserving original color information and achieving good gradation reproduction, preventing false contours while maintaining color fidelity.
2Illumination intensity
If histogram equalization is applied to brightness gradation, then visibility is improved, but color tone changes may occur
Solution Approach 1:
The patent applies histogram equalization selectively to only the luminance component L in the Lch color space, while preserving the chromaticity components ch unchanged. This local quality approach ensures that brightness visibility is improved without altering color tones, as the chromaticity information remains intact during the luminance transformation process.
3Device complexity
If color conversion is performed directly from input to CMYK space, then processing complexity is reduced, but gradation characteristics deteriorate
Solution Approach 1:
The patent segments the color conversion process into distinct stages: first converting to the Lch color space, then applying histogram equalization to the luminance component, and finally converting to CMYK. This segmentation allows independent optimization of brightness gradation (through histogram equalization) without complicating the overall conversion pipeline, maintaining manageable processing complexity while improving gradation characteristics.
Data Source
AI summary
The image formation control apparatus controls an image forming device to execute image forming on an image forming medium based on input image data by using a plurality of color materials including a plurality of chromatic color materials. An image formation control apparatus comprising: a table generating unit to generate a visibility improvement color table by performing color conversion into intermediate image data, performing histogram equalization processing on a brightness gradation value representing brightness of an image represented by the intermediate image data, and adjusting the brightness gradation value representing brightness of the intermediate image data; and an image formation control unit to generate an image forming job for performing the color conversion using the generated color table to form an image on an image forming medium.