Dither Pattern Thresholds for Inkjet Density Control
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Solution Overview
Problem
Existing image processing methods for inkjet printing, such as error diffusion and single dither mask techniques, increase processing load and cost, leading to decreased printing speed and potential irregular density issues due to dot arrangement correlations and lack of robustness against shifting errors.
Innovation Solution
An image processing method using separate dither patterns for different ink colors with shared threshold values in low-gradation ranges and distinct threshold values in intermediate to high-gradation ranges, allowing for high dispersibility of dots and controlled dot overlap to reduce density fluctuations during shifting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If error diffusion processing references density values of other ink color components, then dot arrangement quality improves, but processing load and apparatus complexity increase
Solution Approach 1:
The patent divides the dither pattern into multiple independent patterns corresponding to different ink colors (cyan, magenta, yellow, black). Each color has its own dither pattern that can be processed independently, eliminating the need for complex inter-color dependency processing while maintaining dot arrangement quality.
Solution Approach 2:
The dither patterns are pre-calculated and stored in memory before actual printing operations. This preliminary preparation eliminates the need for complex real-time calculations during printing, reducing processing load and apparatus complexity while maintaining high dot arrangement quality.
2Manufacturing precision
If a single dither mask is used for all ink colors, then dot arrangement without overlap is achieved, but dot correlation increases causing density fluctuation
Solution Approach 1:
The patent introduces asymmetry by creating different dither patterns for different ink colors. The patterns have different threshold value distributions and dot arrangements, which breaks the correlation between colors while maintaining precise dot placement control, thereby reducing density fluctuation.
Solution Approach 2:
Each ink color has its own optimized dither pattern tailored to its specific characteristics. The threshold values and dot arrangements are locally optimized for each color channel, allowing precise control of dot placement while maintaining density consistency across different colors.
3Manufacturing precision
If separate dither patterns with different threshold values are used for all gradation ranges, then dot dispersibility improves, but density fluctuation during shifting increases
Solution Approach 1:
The patent strategically changes threshold value parameters only in specific gradation ranges (intermediate to high density) where dot dispersibility is critical. In low-density ranges, identical threshold values are maintained across colors to ensure density consistency during shifting, achieving a balanced optimization.
Data Source
AI summary
An image processing apparatus includes a generation unit; wherein a first dither pattern and a second dither pattern have same threshold values that are set for same pixels in a first gradation range, and have different threshold values that are set for same pixels in a second gradation range that exceeds the first gradation range; and the generation unit sets a first threshold value for forming dots of the first dither pattern, and generates a first binary data according to whether or not a threshold value corresponding to a target pixel of the first dither pattern is included in the first threshold value, and sets a second threshold value for forming dots of the second dither pattern, and generates a second binary data according to whether or not a threshold value corresponding to a target pixel of the second dither pattern is included in the second threshold value.