Halftone Image Processing for Registration Shift Correction
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Solution Overview
Problem
In color image forming apparatuses, registration shifts due to unevenness or shift in the attachment position of a lens in a deflection scan device cause inclination and curvature of scan lines, leading to image quality issues, particularly in halftone images where interpolation processing can result in density unevenness.
Innovation Solution
An image forming apparatus with a screen processing unit that performs screen processing based on a comparison between pixel values and a dithering matrix threshold, and a determination unit that decides whether a pixel is part of a halftone image by analyzing a region around the pixel, allowing for targeted interpolation processing to correct line transfer positions without affecting halftone images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If interpolation processing is performed to correct line transfer position, then registration accuracy is improved, but density unevenness occurs in halftone images
Solution Approach 1:
The patent applies different processing strategies to different regions of the image based on their characteristics. Character regions undergo interpolation processing to correct registration shifts, while halftone regions skip interpolation to preserve dot patterns and avoid density unevenness. This localized quality approach ensures each region receives appropriate treatment for its specific requirements.
Solution Approach 2:
The image is segmented into different regions (character regions and halftone regions) with distinct processing rules. By dividing the image processing into separate pathways based on region type, the system can apply interpolation only where beneficial (character regions) while avoiding it where harmful (halftone regions), thus resolving the contradiction between registration accuracy and image quality.
2Manufacturing precision
If mechanical adjustment members are added to correct registration shift, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces mechanical adjustment members and physical correction mechanisms with an image processing-based solution. By using software algorithms to detect and correct registration shifts in the image data before printing, the system achieves high registration accuracy without adding any mechanical complexity to the physical apparatus.
Solution Approach 2:
Instead of physically adjusting mechanical parameters of the printing system, the patent changes image data parameters (pixel positions, line transfer positions) through digital processing. This parameter transformation approach allows precise registration correction while keeping the mechanical system simple and unchanged.
Data Source
AI summary
An image forming apparatus in which a lighting position of a dot to be firstly generated by screen processing is changed, in a vertical direction, between a first sub-matrix and a second sub-matrix that are included in a dithering matrix and that are adjacent to each other in a lateral direction, in order not to generate a region where no dot exists in a main scanning direction.