Dither Matrix Screen Angle Adaptation for Halftone Stability
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Solution Overview
Problem
Conventional image forming apparatuses using high-frequency dot patterns in screen processing face issues with rapid tonal changes and tonal loss, leading to unstable density adjustments and reliability concerns, especially in high-density ranges.
Innovation Solution
The implementation of a mechanism that uses dither matrices with threshold values arranged to form halftone dots at different screen angles and rulings based on image density, transitioning from high to low screen-ruling as density increases, to stabilize tonality and prevent tonal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high-frequency dot pattern (high screen-ruling screen) is used in screen processing, then moire occurrence is prevented and dot arrangement precision is improved, but tonal loss occurs rapidly in high-density ranges and dot stability deteriorates
Solution Approach 1:
The patent applies dynamics by making the screen ruling adaptable rather than fixed. The screen ruling is dynamically adjusted based on the input image density: high screen ruling (e.g., 190 lines/mm) is used for low-density images to prevent moire, while low screen ruling (e.g., 134 lines/mm) is used for high-density images to maintain dot stability and prevent tonal loss. This dynamic adaptation resolves the contradiction between precision and stability.
Solution Approach 2:
The patent changes the screen ruling parameter based on image density conditions. By detecting the density of the input image and selecting appropriate screen ruling values (190 lines/mm for low density, 134 lines/mm for high density), the system optimizes both moire prevention and dot stability across different density ranges, resolving the technical contradiction.
2Object-affected harmful factors
If a high-frequency dot pattern is used, then moire is avoided, but tonal change becomes rapid and tonal loss occurs in high-density ranges
Solution Approach 1:
The system dynamically switches screen ruling based on image density to maintain appropriate tonal transitions. For low-density images, high screen ruling prevents moire; for high-density images, low screen ruling maintains gentle tonal changes and prevents tonal loss, thus resolving the contradiction between moire prevention and tonal precision.
Solution Approach 2:
The screen ruling parameter is changed according to image density conditions. The system selects 190 lines/mm for low-density images to prevent moire and 134 lines/mm for high-density images to preserve tonal precision, effectively resolving the contradiction between harmful factor prevention and precision maintenance.
3Manufacturing precision
If LUT is used to adjust density after tonal loss occurs, then density adjustment is attempted, but reliability of adjustment cannot be determined due to unstable latent image
Solution Approach 1:
The patent applies preliminary action by selecting the appropriate screen ruling before screen processing occurs. By pre-determining whether to use high or low screen ruling based on image density analysis, the system prevents tonal loss and maintains stable latent images from the outset, making subsequent density adjustment reliable and deterministic.
Solution Approach 2:
The system provides beforehand cushioning by preventing tonal loss through appropriate screen ruling selection. By using low screen ruling for high-density images, the system cushions against the potential harm of tonal loss and latent image instability, ensuring reliable density adjustment without needing corrective LUT processing.
Data Source
AI summary
Threshold values in a dither matrix are arranged such that, in a case when screen processing is executed on a multi-tone image that has a first density, halftone dots are formed at a first screen angle, and, in a case when screen processing is executed on a multi-tone image that has a density being higher than a second density that is higher than the first density, halftone dots are formed at a second screen angle that is different from the first screen angle.