Variable Dot Printing Masking for Ink Banding Reduction
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Solution Overview
Problem
High-speed ink jet printing is limited by ink drying issues, stepping mismatches, and miss-firing nozzles, leading to visible banding and coalescence in printed images due to ink bleeding and uneven ink distribution.
Innovation Solution
A multi-pass ink jet printing method that applies a mask to print data to vary ink density and decompose pixel sizes into smaller and larger sizes, allowing for superposition of ink dots in subsequent passes to reduce banding and coalescence, while maintaining high printing speeds and improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-pass printing with overlapping bands is used to increase resolution, then manufacturing precision is improved, but ink bleeding and banding occur due to ink concentration variations
Solution Approach 1:
The patent applies a mask to print data before printing to pre-determine which pixels should be printed in the current pass versus subsequent passes. This preliminary action prevents ink bleeding by ensuring that pixels adjacent to band borders are not printed in the current pass if they would cause bleeding in the next pass, thereby maintaining high resolution while preventing banding artifacts.
Solution Approach 2:
The patent applies different masking strategies to different regions of the print data. Specifically, pixels near band borders receive different treatment compared to pixels in the middle of bands. This local differentiation allows the system to maintain high ink concentration and resolution in safe zones while preventing banding in critical border regions through selective masking.
2Manufacturing precision
If ink density is increased in overlapped zones to improve image coverage, then manufacturing precision is improved, but banding occurs due to excessive ink concentration
Solution Approach 1:
The masking process is applied in advance to identify and protect pixels that would cause banding in overlapped zones. By pre-determining which pixels to mask based on their proximity to band borders, the system maintains proper ink coverage in safe zones while preventing excessive ink concentration in critical overlap regions, thereby eliminating banding without sacrificing overall image quality.
3Productivity
If printing speed is increased to improve productivity, then productivity is improved, but ink drying time is insufficient leading to ink bleeding
Solution Approach 1:
The patent applies masking to print data before the printing process, pre-identifying pixels that should be skipped in the current pass to allow proper drying time. This preliminary action enables the system to maintain high printing speeds by not waiting for ink to dry between passes, while still preventing ink bleeding through proactive pixel selection based on masking rules.
4Manufacturing precision
If dot placement accuracy is increased to reduce structural banding, then manufacturing precision is improved, but device complexity increases due to precise feed step adjustment requirements
Solution Approach 1:
The patent introduces a mask as an intermediary layer between the print data and the printing process. This mask absorbs the complexity of precise dot placement requirements by providing a simple binary decision rule (print or skip) for each pixel, thereby reducing the need for complex feed step adjustments while still achieving high dot placement accuracy and eliminating structural banding.
Data Source
Figure 1A~1D
Figure 2A~2B
Figure 2C~2D
AI summary
A method of dot matrix printing comprises a first step of masking print data to obtain masked print data and unmasked print data. The masking comprises decomposing the dot size of one or more pixels into one or more masked dot sizes and one or more unmasked dot sizes such that print data in a first region is masked more per unit area than in a second region. The method comprises a second step of recording on a medium first ink dots in a first pass of a print head, relating to the unmasked print data. A third step of the method comprises recording on the medium second ink dots in one or more following passes of the print head, relating to the masked print data. First and second ink dots related to said one or more pixels are superposed. The first and/or the second ink dots comprise ink dots of different size. A dot matrix printer comprises means for carrying out the method of the invention.