Print-to-print register measurement using cross-correlation
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Solution Overview
Problem
Current methods for measuring print-to-print register in multicolour prints, particularly in security documents like banknotes, require additional space with dedicated register marks and cannot accurately measure register within the effective printed area without compromising the design.
Innovation Solution
The solution involves image processing techniques to measure print-to-print register by finding correspondence between sample images of printed patterns and reference images generated from prepress design data, allowing for precise measurement and correction of print register without the need for special marks, using cross-correlation to extract positional information and compute plate corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If dedicated print register marks are used for measurement, then measurement capability is provided, but additional space is required outside the effective printed area
Solution Approach 1:
The patent makes the printed patterns serve dual purposes: they are both the design elements of the printed material and the measurement references for print-to-print register assessment. By extracting positional information from the actual printed patterns themselves rather than requiring separate dedicated marks, the system eliminates the need for additional space while maintaining measurement capability.
2Difficulty of detecting and measuring
If register marks are placed outside effective printed area, then measurement is enabled, but actual print-to-print register within effective area cannot be measured
Solution Approach 1:
The patent generates reference images from prepress design data that replicate the expected positions and characteristics of the printed patterns. By comparing the actual captured patterns with these reference copies, the system can precisely measure print-to-print register directly within the effective printed area, achieving both measurement functionality and measurement precision.
3Measurement precision
If image processing with cross-correlation is used, then measurement precision is improved, but computational complexity increases
Solution Approach 1:
The patent extracts key positional information from printed patterns by comparing them with reference images using cross-correlation techniques. This extraction approach focuses computational effort on determining the relative position shifts between actual and reference patterns, achieving high measurement precision while keeping the processing complexity manageable by concentrating on essential positional parameters rather than full image analysis.
Data Source
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AI summary
There is described a process of measuring print-to-print register of a multicolour print (A-D) provided in an effective printed area (EPA) of the surface of printed material, which multicolour print (A-D) is formed on the printed material by means of one or more printing presses and includes at least a first pattern (A) and a second pattern (B) distinguishable from the first pattern (A), the effective printed area (EPA) being provided with a matrix arrangement of individual imprints (P) which are each provided with the multicolour print (A-D) and are repeated over the surface of the effective printed area (EPA) along a pattern of rows and columns. Measurement of an actual print-to-print register between the first and second patterns (A, B), as reflected on the printed material, is derived from processing and finding a correspondence between (i) at least one sample image (SIA, SIB) of the printed material covering at least a portion of the first and second patterns (A, B), and (ii) at least one corresponding reference image (RIA, RIB) generated using prepress design data of the first and second patterns (A, B). Furthermore, the process is repeated for multiple ones of the individual imprints (P) so as to derive a set of multiple measurements of the actual print- to-print register between the first and second patterns (A, B) at various imprint locations over the effective printed area (EPA), which set of multiple measurements is mapped into a corresponding print-to-print register map (MB-A, MC-A, MD-A,...) that is representative of print-to-print register deviations at the various imprint locations. Also described is a measuring device for carrying out this process and a process of measuring and correcting print-to-print register of a multicolour print.