Monochrome Image Processing Apparatus Color Discrimination
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Solution Overview
Problem
When printing a full-color document in monochrome, existing grayscale conversion methods reduce color discrimination, as colors with significantly different RGB values are converted to similar gray values, making it difficult to recognize color differences in the resulting grayscale image.
Innovation Solution
An image processing apparatus that converts multi-dimensional color component values into gray values, widening the difference between gray values of colors from different groups while maintaining or increasing the difference within the same color group, ensuring better color discrimination in the monochrome print.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional grayscale conversion methods (NTSC weighted average, sRGB, RGB uniform) are used to convert color images to monochrome, then the conversion process is simple and fast, but the color discrimination is reduced and colors with different RGB values are converted to similar gray values
Solution Approach 1:
The color space is segmented into multiple color groups (red, green, blue, yellow, cyan, magenta) based on hue. Each color group is assigned a distinct gray value range, preventing different color groups from mapping to similar gray values. This segmentation approach maintains color discrimination while keeping the conversion process manageable through predefined grouping rules.
Solution Approach 2:
Different gray value assignment strategies are applied to different color groups. Within the same color group, gray values are assigned to maintain relative luminance relationships. Between different color groups, gray values are deliberately separated to enhance discrimination. This local differentiation approach optimizes both color recognition and grayscale fidelity.
2Measurement precision
If a conversion table with constant gray value difference is used (Japanese Patent Laid-Open No. 2017-38242), then the gray value separation is uniform, but the relationship of magnitude in color difference that can be recognized in the color image is lost
Solution Approach 1:
The gray value assignment parameters are changed based on color group membership. Instead of using a constant gray value difference for all colors, the patent applies different gray value offsets and scaling factors to different color groups. This parameter variation preserves the magnitude relationship of color differences while ensuring adequate gray value separation.
Solution Approach 2:
The patent transforms color information into grayscale by mapping different color groups to distinct gray value ranges while preserving the relative importance and distinction of each color. The conversion process maintains the hierarchical relationship of color differences by assigning gray values that reflect both the hue category and the original color intensity relationships.
Data Source
AI summary
At the time of printing a color page image in monochrome, multi-dimensional color component values of each object included in the color page image are converted into a gray value. Then, in the processing to widen a difference between a first gray value and a second gray value, in a case where a color represented by the first color component value and a color represented by the second color component value do not belong to the same color group, the difference between the first gray value and the second gray value is made larger than that in a case where both the colors belong to the same color group.