Dither Mask Generation for Inkjet Printers to Suppress Halftone Stripes
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Solution Overview
Problem
Existing dither masks used in inkjet printers often generate stripes in halftone images due to non-uniform nozzle ejection rates, leading to print quality issues like banding and density irregularities.
Innovation Solution
A dither mask generation method that sets a nozzle relative ejection rate for each nozzle, limits the nozzle ejection rates within each raster, and sets thresholds based on these rates to prevent excessive differences between adjacent rasters and path groups, thereby reducing the occurrence of stripes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a dither mask is generated with non-uniform nozzle ejection rates to suppress banding, then density irregularity is reduced, but stripes are easily generated in halftone images
Solution Approach 1:
The patent applies local quality by differentiating nozzle ejection rate settings between end nozzles and intermediate nozzles. Specifically, end nozzles are assigned lower ejection rates while intermediate nozzles have higher ejection rates, creating localized variations that suppress banding. This is achieved through setting different threshold values in the dither mask for different nozzle groups, thereby addressing density uniformity issues without causing excessive stripe generation.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting threshold values in the dither mask based on nozzle position and ejection rate characteristics. The threshold values are modified to compensate for variations in nozzle performance, particularly for end nozzles that tend to have lower ejection rates. This parameter adjustment allows the system to maintain density uniformity while controlling stripe formation through careful threshold selection.
2Object-generated harmful factors
If uniform nozzle ejection rates are used in dither mask, then stripes are reduced, but banding and density irregularities occur
Solution Approach 1:
The patent implements local quality by assigning different ejection rate characteristics to different spatial regions of the nozzle array. End nozzles are given lower ejection rate targets while intermediate nozzles receive higher targets, creating a non-uniform but controlled distribution that adapts to the physical characteristics of the print head. This localized differentiation resolves density uniformity issues that arise from uniform ejection rate assumptions.
Solution Approach 2:
The patent incorporates feedback mechanisms by using measured or estimated nozzle ejection rate data to inform dither mask generation. The system adjusts threshold values based on feedback regarding actual nozzle performance, particularly compensating for the lower ejection rates observed in end nozzles. This feedback-driven approach allows the system to maintain both stripe reduction and density uniformity by adapting to actual nozzle behavior.
3Manufacturing precision
If dither mask suppresses banding through non-uniform nozzle usage, then print quality improves, but complexity of dither mask generation increases
Solution Approach 1:
The patent applies segmentation by dividing the nozzle array into distinct groups (end nozzles versus intermediate nozzles) and applying different ejection rate settings to each group. This segmentation simplifies the dither mask generation process by reducing the problem from individual nozzle control to group-level control, thereby improving print quality through manageable complexity rather than overwhelming individual nozzle optimization.
Data Source
AI summary
The dither mask generation method includes: a process of setting a nozzle relative ejection rate which is a control target of the nozzle ejection rate and stipulates a relative using ratio of the individual nozzles; a process of setting a nozzle pattern indicating correspondence relation between individual pixels of the dither mask and the nozzles in charge of recording at respective pixel positions; a process of setting an upper limit to the nozzle ejection rates of the individual nozzles for each raster in a main scanning direction, regarding at least some thresholds; and a process of setting the thresholds to the pixels of the dither mask based on the nozzle relative ejection rate, the nozzle pattern and a limitation by the upper limit.