Halftone Dot Pattern Stabilization in Image Processing Apparatus
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Solution Overview
Problem
In tandem-type color image forming apparatuses, the electrophotographic process faces challenges with misregistration and color unevenness due to pixel level differences caused by shifting processing, especially when converting high-resolution image data to low-resolution data for spot-multiplexing, leading to noticeable halftone dot changes and color inconsistencies in printed images.
Innovation Solution
An image processing apparatus that includes a halftone processing unit applying dither matrix-based halftone processing, a correction unit shifting pixel data in the sub-scanning direction to correct distortion, and a resolution conversion unit ensuring matched halftone dot patterns before and after the correction position, thereby stabilizing halftone dot reproduction across different resolution conversions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If shifting processing is applied to high-resolution image data to correct scanning line distortion, then manufacturing precision is improved, but color unevenness occurs due to halftone dot pattern changes at correction positions
Solution Approach 1:
The patent applies halftone processing before shifting processing to pre-establish the halftone dot patterns. This preliminary action ensures that when shifting processing corrects scanning line distortion, the halftone dot patterns are already in place and can be properly maintained or adjusted at correction positions, preventing color unevenness from occurring.
Solution Approach 2:
The patent changes the processing sequence by performing halftone processing first (converting image data to halftone dot patterns) and then applying shifting processing. This parameter change in processing order allows the system to maintain consistent halftone dot patterns across correction positions while still achieving distortion correction, thereby eliminating color unevenness.
2Productivity
If resolution conversion processing is applied after shifting processing to convert high-resolution data to low-resolution data for spot-multiplexing, then productivity is improved, but halftone dot patterns become inconsistent at correction positions
Solution Approach 1:
The patent performs halftone processing as a preliminary step before both shifting processing and resolution conversion processing. This establishes the halftone dot patterns early in the processing chain, ensuring they remain consistent through subsequent operations. The preliminary halftone processing creates a stable foundation that maintains pattern consistency even when resolution conversion is applied for spot-multiplexing.
3Device complexity
If shifting processing is applied to low-resolution image data, then device complexity is reduced, but pixel level difference becomes more noticeable causing color unevenness
Solution Approach 1:
The patent applies halftone processing before shifting processing regardless of the resolution level. This preliminary action converts the image data to halftone dot patterns first, which makes the subsequent shifting processing less visible and reduces the noticeable pixel level differences. By establishing the halftone structure beforehand, the shifting operation becomes less disruptive to image quality.
Data Source
AI summary
An image processing apparatus includes a halftone processing unit configured to apply halftone processing based on a dither matrix to image data, a correction unit configured, with respect to the processed image data, to shift a pixel of the image data in a sub-scanning direction at a correction position in a main scanning direction which is determined based on correction information for correcting a distortion due to a curve of a scanning line for forming an image according to the image data, and a resolution conversion unit configured to apply resolution conversion processing for lowering a resolution of image data to the corrected image data, wherein the dither matrix results in that the image data to which the resolution conversion processing has been applied includes matched portions of halftone dot patterns appearing in regions preceding and following the correction position in the main scanning direction.