Dither Pattern Forming for Multi-Scan Printing
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Solution Overview
Problem
Existing multi-pass printing methods suffer from density unevenness and graininess due to printing position displacement, as they lack control over the arrangement of dots on the print medium, leading to inadequate density and hue variations, especially in low gradation regions.
Innovation Solution
The implementation of a dither pattern with distinct thresholds for each printing scan, allowing for active control over dot arrangement, uses a dither method for quantization instead of error diffusion, and adjusts the number and dispersion of overlapping dots to minimize density and graininess variations across the entire gradation range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multi-pass printing is performed using mask patterns with complementary relationship, then density information is preserved and stripes are inhibited, but dots have completely exclusive relationship causing density unevenness when conveyance error occurs
Solution Approach 1:
The patent applies local quality by differentiating the treatment of dots based on their position and function. Overlapping dots (printed by multiple scanning lines) are given special status compared to non-overlapping dots. The control information is locally applied to specific pixel groups that correspond to overlapping dot positions, allowing selective adjustment of dot printing behavior in critical areas while maintaining standard behavior elsewhere.
Solution Approach 2:
The patent implements preliminary action by pre-calculating and pre-arranging overlapping dots before actual printing occurs. The image processing section identifies positions where dots will overlap across multiple scanning lines and prepares control information in advance. This preliminary arrangement ensures that when conveyance errors occur, the overlapping dots are already positioned to compensate for potential displacement, maintaining density uniformity.
2Manufacturing precision
If multi-valued image data is divided into portions for individual printing scans and binarized independently by error diffusion, then dots do not have exclusive relationship, but dot arrangement cannot be actively controlled leading to graininess and density variation
Solution Approach 1:
The patent applies local quality by differentiating the treatment of dots based on their position and function. Overlapping dots (printed by multiple scanning lines) are given special status compared to non-overlapping dots. The control information is locally applied to specific pixel groups that correspond to overlapping dot positions, allowing selective adjustment of dot printing behavior in critical areas while maintaining standard behavior elsewhere.
Solution Approach 2:
The patent uses copying by creating a reference pattern of overlapping dot positions from the multi-valued image data. This reference pattern is then used to generate control information that guides the binarization process. Instead of directly binarizing divided image data independently, the system copies the spatial arrangement information from the original multi-valued data to control where overlapping dots should be formed, ensuring consistent and controllable dot arrangement across multiple printing scans.
3Manufacturing precision
If conventional multi-pass printing is used, then processing complexity is low, but active control over dot arrangement is lacking resulting in poor density expression in low gradation regions
Solution Approach 1:
The patent applies segmentation by dividing the image processing into distinct functional sections: an image processing section that identifies overlapping dot positions and generates control information, and a printing section that executes printing based on this control information. This segmentation allows the complex task of controlling dot arrangement to be handled in a modular fashion, where the image processing section prepares the necessary control data without burdening the printing hardware with complex decision-making logic.
Solution Approach 2:
The patent introduces an intermediary element in the form of control information that mediates between the image data and the printing process. This control information, generated by the image processing section, serves as an intermediary that carries the spatial arrangement instructions for overlapping dots to the printing section. This intermediary layer enables active control over dot arrangement without requiring direct complex interaction between the image data and printing hardware, thus managing processing complexity effectively.
Data Source
AI summary
In order to print a unit area of a print medium by a first printing scan and a second printing scan, dither patterns are formed which can control the arrangement of dots on the print medium without adverse effects of density unevenness and graininess, that are caused by printing position displacement. Regarding first and second dither patterns, information indicating whether or not a threshold is already set to a reference pixel and one or more pixels around the reference pixel in the first dither pattern is obtained for cases where each pixel in the first dither pattern is the reference pixel. A pixel in the second dither pattern to which a predetermined pixel is to be set is determined based on the obtained information. The first and second dither patterns formed in the above manner are associated with the first printing scan and the second printing scan, respectively.