Dither Matrix Generation for Halftone Image Texture Suppression
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Solution Overview
Problem
Existing image forming apparatuses using the electrophotographic method face challenges in reproducing halftone images, leading to anomalous textures and moiré effects in low density regions due to the concentration of dots and the requirement for large threshold tables.
Innovation Solution
An image forming apparatus and dither matrix generation method that alternately increase the size of first and second dots until they reach specific sizes, then focus on increasing the size of one dot while keeping the other constant, and finally increase both dots uniformly, using a threshold matrix with multiple dot sizes to control density and suppress texture formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dots are caused to appear randomly by using an FM screen in a low density region, then tone reproduction is achieved, but an extremely large threshold table is required
Solution Approach 1:
The threshold matrix is divided into multiple sub-matrices, each handling a specific density range. This segmentation allows the system to use smaller, more manageable threshold tables while maintaining accurate tone reproduction across the full density range.
Solution Approach 2:
Different sub-matrices are designed with different dot growth characteristics optimized for specific density regions. Low density regions use one growth pattern while high density regions use another, allowing each region to be handled with appropriately sized threshold tables.
2Manufacturing precision
If growth is performed while causing dots to concentrate using a threshold matrix of a sub-matrix method, then dot size control is achieved, but an anomalous texture occurs at a low period in a low density region
Solution Approach 1:
The patent introduces asymmetric dot growth patterns where first and second dots grow at different rates and follow different sequences. This asymmetry disrupts the periodicity that causes anomalous textures while maintaining precise dot size control through the structured threshold matrix design.
Solution Approach 2:
The patent uses periodic dot growth patterns with carefully controlled periods to prevent the formation of low-period textures. By orchestrating the periodic appearance and growth of dots in a structured sequence, the system achieves smooth density transitions without visible texture patterns.
3Reliability
If there is a possibility that the texture will be visually recognized as moiré, then image quality is affected, but the use of larger threshold tables could suppress it
Solution Approach 1:
Dividing the threshold matrix into sub-matrices reduces the size of individual threshold tables while collectively covering the full density range. This segmentation prevents the formation of large-scale periodic patterns that cause moiré, maintaining image quality without requiring an excessively large single threshold table.
Solution Approach 2:
The patent changes the parameters of dot growth by introducing multiple dot sizes and asymmetric growth patterns. These parameter changes disrupt the regular periodicity that leads to moiré effects, allowing suppression of visible textures while using manageable threshold table sizes.
Data Source
AI summary
For a dither matrix used when converting multivalued data into image data for an output apparatus, thresholds are set such that a first dot and a second dot alternately become larger until both of the first dot and the second dot reach a first dot size, after both of the first dot and the second dot reach the first dot size, the first dot becomes larger until the first dot reaches a second dot size while the second dot does not become larger, and, thereafter, the second dot becomes larger until the second dot reaches the second dot size while the first dot does not become larger, and after both of the first dot and the second dot reach the second dot size, the first dot and the second dot alternately become larger.