Monochrome Image Density Signal Conversion for Paper Tone Compensation
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Solution Overview
Problem
Monochrome images output on different recording media with varying paper white color tones appear unnatural due to the influence of paper white color tones, as existing technologies fail to adjust color tones effectively across multiple media types.
Innovation Solution
An image forming apparatus with a recording medium selecting unit, mode setting unit, and signal converting unit that sets the color tone of intermediate-density portions to a*=A in the CIE-L*a*b* space, reducing the influence of paper white color tones, allowing high-quality monochrome images to be produced regardless of the recording medium's unique color tone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If color tone adjustment is performed according to paper white deviation, then color matching on different recording media is improved, but the color tone of intermediate-density portions becomes unnatural and inconsistent across media types
Solution Approach 1:
The patent applies different adjustment strategies to different density regions of the image. For intermediate-density portions (a key local region), it maintains fixed color tone at a*=A regardless of paper white. For other regions like highlights and shadows, it allows adjustment according to paper white deviation. This local differentiation resolves the contradiction by preserving visual naturalness in the most visually critical intermediate-density areas while still adapting to different media characteristics in other regions.
Solution Approach 2:
The patent changes the adjustment parameter strategy based on density region. Instead of uniformly adjusting all pixels according to paper white deviation, it selectively applies parameter changes: fixed a*=A for intermediate-density portions and paper-white-adapted parameters for other portions. This selective parameter change approach maintains both color matching precision and visual naturalness across different recording media.
2Adaptability or versatility
If monochrome image is output on recording media with different paper white color tones, then versatility across media types is improved, but the color tone consistency deteriorates due to paper white influence
Solution Approach 1:
The patent maintains color tone consistency in the visually dominant intermediate-density regions by fixing a*=A across all media types, while allowing flexibility in other density regions. This local quality approach ensures that the most perceptually important portions maintain stability, achieving both versatility and perceived consistency.
Solution Approach 2:
The patent introduces an intermediary control mechanism that decouples the relationship between paper white color tone and intermediate-density image color tone. By using a fixed reference point (a*=A) as an intermediary target for intermediate-density portions, it prevents direct transmission of paper white variations to the image content, thereby maintaining consistency across diverse media types.
3Adaptability or versatility
If color tone is changed in accordance with paper white, then adaptation to recording medium is improved, but the visual naturalness of monochrome photograph deteriorates
Solution Approach 1:
The patent selectively applies paper white adaptation only to non-intermediate-density regions, while preserving fixed color tone in intermediate-density portions. This local differentiation maintains visual naturalness where it matters most (intermediate tones that dominate monochrome perception) while still providing medium adaptation in other regions.
Solution Approach 2:
The patent converts the potentially harmful effect of paper white influence into a beneficial selective adaptation strategy. By allowing paper white to influence only specific density regions (non-intermediate portions) while protecting critical intermediate-density regions, it transforms the problem of paper white variation into a controlled, region-specific adaptation feature that preserves overall visual naturalness.
Data Source
AI summary
In a recording medium selecting step, a recording medium on which an image is to be formed is selected from among a plurality of recording media having unique color tones. In a mode setting step, it is determined whether the image is to be output in a monochrome mode. In a signal converting step, a luminance signal corresponding to the image is converted into a density signal when the monochrome mode is set in the mode setting step. In a forming step, an image is formed on the recording medium selected in the recording medium selecting step according to the density signal. The signal converting step is controlled so that a color tone of an intermediate-density portion of the image formed on the recording medium is set to be near a*=A in the a*b* plane of the CIE-L*a*b* space, where A is a constant.