Frequency-Shifted Halftone Moiré Patterns for Color Misregistration
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Solution Overview
Problem
Multi-color printing systems face challenges in accurately characterizing misregistration between color separations, leading to noticeable color shifts and undesirable moiré patterns due to mechanical issues and non-linear color mixing, which existing techniques struggle to effectively mitigate.
Innovation Solution
A method and system utilizing a misregistration estimation patch formed by frequency-shifted halftone patterns that create a moiré pattern, allowing for the detection and measurement of color separation misregistration by analyzing the periodic color variations and shifts in the moiré pattern, enabling corrective adjustments to digital files and mechanical settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency-shifted halftone patterns are used to form moiré patterns for misregistration estimation, then measurement precision of color separation misregistration is improved, but device complexity increases due to the need for specialized test patches and analysis algorithms
Solution Approach 1:
The patent uses a digital test patch containing frequency-shifted halftone patterns that replicates the printing process conditions. By scanning this test patch and analyzing the resulting moiré pattern, the system creates a digital model of the misregistration without requiring complex physical measurement apparatus. The digital analysis of chroma and luminance variations in the moiré pattern provides precise misregistration measurements while keeping the physical system relatively simple.
Solution Approach 2:
The moiré pattern serves as an intermediary that translates small misregistration displacements into large, easily measurable chroma and luminance variations. Instead of directly measuring the tiny misregistration distance, the system uses the moiré effect to amplify the signal into visible periodic color variations that can be analyzed through standard image processing, thereby improving measurement precision without requiring ultra-precise measurement hardware.
2Device complexity
If physical registration marks are used for misregistration estimation, then device complexity is reduced, but measurement precision deteriorates due to limited measurement locations and manual examination requirements
Solution Approach 1:
The test patch is divided into multiple regions containing different frequency-shifted halftone patterns, allowing simultaneous measurement of misregistration at multiple locations and in multiple directions. Each region provides independent measurement data, enabling comprehensive characterization of misregistration across the entire printing system rather than at a single point, thereby improving overall measurement precision while maintaining system simplicity.
Solution Approach 2:
The patent transitions from one-dimensional line-based registration marks to two-dimensional frequency-shifted halftone patterns. This dimensional change enables measurement of misregistration in both horizontal and vertical directions simultaneously, as well as providing information about rotational misalignment, thereby significantly improving measurement precision without adding mechanical complexity.
3Object-affected harmful factors
If rotated halftone screens are used for different color separations, then moiré patterns are reduced, but misregistration characterization capability is lost
Solution Approach 1:
The patent extracts the misregistration measurement function from the normal printing process by using a separate test patch with specifically designed frequency-shifted halftone patterns. This allows the production printing to use rotated screens for moiré reduction while the test patch independently provides misregistration characterization data, thereby resolving the contradiction by separating these two functions into different operational contexts.
Solution Approach 2:
The test patch with frequency-shifted halftone patterns is printed as a preliminary step before or alongside production printing. By pre-establishing the moiré pattern through controlled frequency shifts in the test patch, the system enables subsequent analysis of misregistration without affecting the production print quality. This preliminary action allows misregistration measurement while maintaining rotated screen configurations for actual printing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables precise estimation and characterization of color separation misregistration, reducing unwanted artifacts like moiré patterns and color shifts, thereby improving print quality by allowing for targeted adjustments in trap settings and digital image processing.
Implementation Method 1
The first and second halftone patterns may form a moiré pattern. A deviation in the position of peaks and valleys of the moiré pattern can be indicative of a local color separation misregistration
Data Source
AI summary
A method and system for estimating color separation misregistration of a printing system. The method may include marking a substrate to form a misregistration estimation patch. The misregistration estimation patch being formed by first and second color separations. The first color separation marking the substrate with a first halftone pattern. The first halftone pattern has a first halftone-frequency vector in a first direction and a second halftone-frequency vector in a second direction. The second color separation marking the substrate with a second halftone pattern. The second halftone pattern has a first halftone-frequency vector in a first direction and a second halftone-frequency vector in a second direction. The first and second halftone patterns form a moiré pattern. A deviation in at least one the halftone frequency vectors and/or the moiré pattern can be indicative of a color separation misregistration. The method also includes estimating the color separation misregistration of the printing system using the misregistration estimation patch.