Multi-Color Shading Processor for Inkjet Nozzle Ejection Variation
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Solution Overview
Problem
Inkjet printing technologies face challenges in achieving uniform color images due to variations in nozzle ejecting characteristics, leading to color unevenness and recognition of color banding, even when conventional head shading techniques are applied.
Innovation Solution
The implementation of a Multi-Color Shading (MCS) processor and correction processing that adjusts image data before quantization, using a conversion table to account for variations in nozzle ejecting characteristics, ensuring accurate color reproduction across different nozzle groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If head shading technique is used to correct density unevenness, then density uniformity is improved, but color accuracy deteriorates due to color deviation in composite colors
Solution Approach 1:
The invention divides the correction process into two distinct stages: head shading correction for density uniformity and MCS correction for color accuracy. The MCS processor segments the correction function by calculating separate correction values for each nozzle group based on their specific ejecting characteristics, allowing independent optimization of both density and color without interference between the two correction objectives
Solution Approach 2:
The MCS correction values are calculated in advance during system initialization or calibration, storing the correction data in a lookup table. This preliminary action allows the correction to be applied during normal printing operations without real-time computation, ensuring both density uniformity and color accuracy are maintained while avoiding the trade-off during actual printing
2Manufacturing precision
If conventional head shading is applied to nozzles with varying ejection volumes, then density unevenness is reduced, but color banding appears in composite color regions
Solution Approach 1:
The MCS processor implements local quality by assigning unique correction values to each nozzle group based on their specific ejecting characteristics. Instead of applying a uniform correction across all nozzles, the system tailors the correction to local variations in nozzle performance, ensuring that each nozzle group contributes appropriately to composite colors without creating visible banding artifacts
Solution Approach 2:
The invention changes the correction parameter from simple dot number adjustment (conventional head shading) to a comprehensive correction value that accounts for both dot number and ink ejection characteristics. By modifying the correction parameter to include nozzle-specific ejecting characteristics, the system eliminates color banding while maintaining density evenness in composite color regions
Data Source
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Figure 3A~3C
AI summary
An image processor (300), a printing apparatus (100), and an image processing method are provided that can reduce, when a plurality of types of inks are used to print an image, the color unevenness that is caused by the variation of ejecting characteristics among a pluralities of nozzles. To realize this, for a color formed by overlapping at least two colors of inks, parameters are prepared that are determined so as to reduce the color difference in the printing medium (106) due to the variation of the ejecting characteristic among the respective pluralities of nozzles (101, 102, 103, 104). During printing, the parameters are used to correct the first color signal owned by the individual pixels to the second color signal.