Inkjet Printer Color Correction via Multi-Stage Shading
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Solution Overview
Problem
Existing image processing technologies face challenges in accurately reducing color unevenness in color images formed by the variation in ejection characteristics among ink nozzles, leading to color shifts and inaccuracies in color reproduction, especially when multiple inks are superimposed.
Innovation Solution
An image processing apparatus and method that performs color correction using a Multi Color Shading (MCS) processing unit, which generates and applies correction tables to adjust ink ejection amounts across nozzles, ensuring consistent color output by analyzing and correcting pixel values before quantization, thereby reducing color unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If head shading technique is used to correct density variation, then density unevenness of single color image is corrected, but color shift occurs when two or more inks are superimposed
Solution Approach 1:
The correction process is segmented into two distinct stages: head shading correction for density uniformity and MCS correction for color accuracy. The head shading technique first corrects density variation by adjusting the number of printing dots for each nozzle based on ejection amount measurements. Then, the MCS processing unit performs additional color correction by modulating ink ejection amounts for specific color combinations, separating the density correction function from the color accuracy function to resolve the contradiction.
Solution Approach 2:
The head shading correction is performed as a preliminary action before MCS color correction. By first establishing uniform density across all nozzles through head shading, the foundation is prepared for subsequent color accuracy correction. This preliminary density uniformity correction enables the MCS processing to focus specifically on color fidelity without being confounded by density variations.
2Measurement precision
If spectrophotometric colorimeter is used for colorimetry, then color measurement is performed, but colorimetric error occurs due to reading reflected light within spot diameter including surrounding regions
Solution Approach 1:
The MCS correction targets specific local regions where color unevenness occurs due to nozzle variations. By identifying and correcting color deviations in specific areas (such as regions affected by particular nozzles with abnormal ejection characteristics), the system achieves accurate colorimetry results that reflect actual perceived color quality, compensating for the spectrophotometric colorimeter's inability to isolate small defect regions.
3Adaptability or versatility
If multiple inks are superimposed for color reproduction, then color image is formed, but color unevenness occurs due to variation in ejection characteristic among nozzles
Solution Approach 1:
The system incorporates feedback mechanisms where ejection characteristics of individual nozzles are measured and used to generate correction parameters. The MCS processing unit receives feedback on color unevenness from test images and adjusts ink ejection amounts accordingly. This closed-loop feedback system continuously optimizes color uniformity by comparing actual output with target values and applying corrective modulation to ink ejection for different color combinations.
Solution Approach 2:
The MCS processing dynamically changes ejection parameters (ink ejection amounts) based on the specific combination of inks being superimposed. By modulating the ejection amount parameters for different nozzle-ink combinations, the system compensates for manufacturing variations and maintains color uniformity across the printed image, enabling versatile color reproduction without sacrificing precision.
Data Source
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AI summary
An image processing apparatus is provided that is capable of very accurately and efficiently reducing uneven color caused by variation in ejection characteristics among nozzles that eject ink and that occurs in a color image that is formed by mixing a plurality of different kinds of ink. A patch is printed by ejected ink from a plurality of nozzles, a region is specified so as to perform color correction in a test color image that is printed on a printing medium, a plurality of different color correction processing is performed on color signals that correspond to a color correction region, a plurality of color correction patches are printed, a color correction patch to be used is selected from among the plurality of different color correction patches and table parameters that correspond to the nozzles are created based on the selected color correction processing.