Inkjet Rasterization Lookup Table Compensation
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Solution Overview
Problem
Inkjet printing machines face challenges in achieving homogeneous density across the printing direction due to nozzle scatter and mechanical variances, leading to inhomogeneous prints, and existing compensation methods are either time-consuming or prone to artifacts.
Innovation Solution
The method involves calibrating the rasterization process by assigning specific gray values to raster patterns based on the performance of individual print nozzles, using a matrix of lookup tables that account for nozzle positions to efficiently compensate for density fluctuations during the printing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pre-compensation is performed on gray value images before screening using compensation profiles, then density homogeneity is improved, but processing time increases and online capability is limited
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing position-dependent compensation values in a lookup table during an offline calibration phase. The system performs test prints, measures density variations, and computes compensation factors in advance, so that during online operation only a simple table lookup and value application are needed, eliminating time-consuming real-time calculations while maintaining density homogeneity.
Solution Approach 2:
The patent implements beforehand cushioning by creating a compensation lookup table that anticipates and stores correction values for all possible positions and area coverages before actual printing. This pre-prepared compensation data acts as a cushion that absorbs density variations during printing without requiring real-time processing, enabling both high precision and fast online operation.
2Measurement precision
If compensation profiles are determined for multiple area coverages, then density compensation accuracy is improved, but data complexity and processing requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the compensation data into a structured lookup table with discrete entries for different area coverage ranges and nozzle positions. Instead of storing continuous complex functions, the system segments the parameter space into manageable discrete levels (e.g., area coverage ranges from 0-10%, 10-20%, etc.), creating a compact tabular structure that balances accuracy with reduced data complexity.
Solution Approach 2:
The patent uses parameter changes by discretizing continuous parameters (area coverage, nozzle position) into finite levels for the lookup table. This transforms the complex continuous compensation problem into a manageable discrete parameter system where accuracy is maintained through sufficient granularity while complexity is reduced through finite state representation.
3Adaptability or versatility
If interpolation methods are used to map compensation parameters, then coverage of continuous parameter space is improved, but introduction of artifacts and loss of image properties occurs
Solution Approach 1:
The patent applies local quality by creating position-specific lookup table entries for each nozzle position and area coverage combination rather than using uniform interpolation across the entire parameter space. This ensures that compensation values are locally optimized for each specific printing condition, maintaining image properties like gradients and noise characteristics while adapting to local density variations without introducing interpolation artifacts.
Data Source
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AI summary
Method for compensating position-dependent density fluctuations (8) in an inkjet printing machine (3) by a computer (1), wherein, within the framework of the calibration of a raster image processor (2) of the inkjet printing machine (3), specific raster patterns (7) are assigned to specific gray values of a color separation of a print image to be rasterized by means of a look-up table (6, 6a), these raster patterns (7) are used by the computer (1) for rasterizing the print image, and the rasterized print image (4) is printed on the inkjet printing machine (3), which is characterized in that the look-up table (6b) contains as an additional variable the position of each print nozzle of the print heads of the inkjet printing machine (3), and for each position of a print nozzle in the look-up table (6b), a complete set of gray values with assigned, adapted raster patterns (7) is entered by the computer (1).