Halftone Screen Harmonic Angles for Moiré Reduction
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Solution Overview
Problem
Moiré interference patterns, resulting from color plane mis-registration, negatively impact image quality in printing systems, particularly in digital printing where low LPI halftone screen resolutions limit the reduction of rosette structures.
Innovation Solution
The implementation of amplitude modulated halftones that satisfy a harmonic condition between halftone screens, with specific angular separations and resolutions, such as 45 degrees and a ratio of ½√{square root over (2)}, to minimize moiré interference and improve print quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional halftone screens are used in digital printing, then the printing process is simple and fast, but moiré interference patterns appear and image quality deteriorates
Solution Approach 1:
The patent changes the parameters of halftone screens by imposing harmonic relationships between their frequencies and orientations. Specifically, it uses frequency ratios like 1:√2:√3 and angular separations like 30°, 45°, 60° to ensure that dot patterns from different color planes do not create moiré interference, thus maintaining image quality while preserving printing efficiency
Solution Approach 2:
The patent converts the potentially harmful moiré interference into a benefit by deliberately designing halftone screens with harmonic relationships. This intentional structuring transforms what would normally be random interference patterns into controlled, non-interfering patterns that actually improve print quality by eliminating unwanted artifacts
2Object-affected harmful factors
If LPI of halftone screen is increased to reduce rosette structures, then moiré interference is reduced, but the maximum resolution is exceeded and printing becomes impractical
Solution Approach 1:
Instead of increasing LPI beyond practical limits, the patent changes the approach by using harmonic frequency relationships between color planes. This allows the use of achievable LPI values (like 160 LPI and 225 LPI in the embodiment) while still eliminating rosette structures through proper frequency and angular relationships
3Object-affected harmful factors
If halftone screens are overlaid at different angles to reduce moiré, then interference patterns are minimized, but color plane mis-registration increases and image quality deteriorates
Solution Approach 1:
The patent optimizes the angular separation parameters between halftone screens to specific values (30°, 45°, 60°) that simultaneously achieve two goals: creating sufficient angular difference to prevent moiré interference while maintaining small enough angles to minimize the impact of color plane mis-registration. This balanced parameter selection resolves the contradiction between reducing moiré and maintaining registration accuracy
Data Source
AI summary
A halftone comprises a first halftone screen and a second halftone screen. The first halftone screen comprises a first plurality of amplitude modulated dots arranged according to a first plurality of rows, the first plurality of rows being orientated according to a first direction and comprising a first dot spacing. The second halftone screen comprises a second plurality of amplitude modulated dots arranged according to a second plurality of rows, the second plurality of row being orientated in a second direction and comprising a second dot spacing. The first direction and the second direction define an angle of 45 degrees or less and a ratio of the second dot spacing to the first dot spacing is less than one.