Color Calibration for Image Forming Apparatus Using Monochromatic Patch Analysis
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Solution Overview
Problem
Current image forming apparatus calibration techniques struggle to accurately adjust for variations in image density due to environmental changes and component fluctuations, particularly for colors beyond process colors like cyan, magenta, yellow, and black, leading to poor color reproduction, especially in highlight and halftone ranges.
Innovation Solution
An image processing apparatus and method that acquires colorimetric values from monochromatic patches on a calibration chart, converts these values along with a maximum tone value into a specific color system value, and determines a new target characteristic to improve tone reproducibility across different types of sheets by generating a tone reproduction curve (γ table) that accounts for varying print characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional density-based calibration is used for process colors, then calibration can be performed for cyan, magenta, yellow, and black, but it cannot be applied to colors other than process colors
Solution Approach 1:
The patent changes the calibration parameter from density (traditional method) to colorimetric values (L*a*b* system). This parameter change enables calibration for any monochromatic color, not just process colors, while maintaining measurement precision through the use of a colorimeter that directly measures colorimetric properties.
2Adaptability or versatility
If a fixed target characteristic is used for calibration, then the calibration process is simple, but it cannot adapt to various sheets with different print characteristics
Solution Approach 1:
The patent makes the target characteristic dynamic by determining it based on the measured colorimetric values and maximum tone value for each specific sheet type. Instead of using a fixed target, the system adapts the target characteristic to match the actual print characteristics of the sheet being calibrated, enabling versatility across different sheets while managing complexity through automated determination.
Solution Approach 2:
The patent performs preliminary measurement of colorimetric values and maximum tone value before determining the target characteristic. This preliminary action provides the necessary data to calculate an appropriate target that adapts to the specific sheet properties, enabling the system to handle various sheet types without requiring complex real-time adjustments during the calibration process.
3Manufacturing precision
If conventional calibration methods are used, then the process is straightforward, but tone reproducibility in highlight and halftone ranges is poor
Solution Approach 1:
The patent uses feedback from colorimeter measurements of actual printed patches to determine the target characteristic. By measuring the actual colorimetric values and maximum tone value achieved during printing, the system adjusts the target to ensure accurate tone reproduction in highlight and halftone ranges, improving manufacturing precision through iterative measurement and adjustment.
Solution Approach 2:
The patent replaces traditional density-based mechanical measurement with optical colorimetric measurement using a colorimeter. This substitution enables more precise measurement of color properties, particularly in highlight and halftone ranges where density measurements are less effective, thereby improving tone reproducibility through more accurate optical characterization.
Data Source
AI summary
An image processing apparatus includes circuitry that acquires a colorimetric value for each of a plurality of patches on a first chart printed out by an image forming apparatus and read by a colorimeter. Each of the patches has a monochromatic color. The circuitry further acquires a maximum tone value previously set in accordance with a sheet, and converts each of the colorimetric value, the maximum tone value, and a color system value of a first target into a particular color value. The first target represents an ideal characteristic of the color system value corresponding to a tone value. The circuitry further determines, as a second target, a characteristic passing through a point determined by a color value corresponding to the maximum tone value. The characteristic is generated based on the color system value of the first target converted into the particular color value.