Print Head Quantization Mask Selection for Frequency Uniformity
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Solution Overview
Problem
Existing image processing techniques, such as head shading, while reducing density unevenness in print elements, introduce frequency unevenness due to variations in print characteristics, leading to differences in spacial frequency and visual quality issues.
Innovation Solution
An image processing apparatus and method that corrects image data for each printing element group based on print characteristics and selects a quantizing mask with a smaller granularity difference between unit areas, using masks with different spacial frequency characteristics to minimize frequency unevenness during the printing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If head shading correction is applied to compensate for nozzle ejection variations, then density unevenness is reduced, but frequency unevenness is introduced due to different spatial frequencies in dot arrangements
Solution Approach 1:
The patent applies different quantization masks to different regions (processing units) based on their specific nozzle characteristics. Each processing unit uses a quantization mask selected to match its dot arrangement pattern, ensuring local optimization of spatial frequency characteristics while maintaining overall density uniformity across the print head.
Solution Approach 2:
The patent changes the quantization parameters (spatial frequency characteristics of quantization masks) based on the specific ejection characteristics of each processing unit. By selecting quantization masks with appropriate spatial frequencies that match the dot arrangement patterns of each region, the patent eliminates frequency unevenness while preserving density correction benefits.
2Productivity
If quantization is performed on corrected image data, then digital values are converted to printable dot patterns, but different spatial frequency patterns are generated across processing units causing visual unevenness
Solution Approach 1:
The patent assigns different quantization masks with appropriate spatial frequency characteristics to different processing units based on their specific nozzle ejection characteristics. This local customization ensures that each region's quantized dot pattern matches its inherent dot arrangement, maintaining spatial frequency uniformity across the entire print output.
Solution Approach 2:
The patent divides the print head into multiple processing units and applies different quantization strategies to each segment. By segmenting the quantization process and tailoring the quantization mask selection to each processing unit's characteristics, the patent achieves both efficient quantization and uniform spatial frequency output.
Data Source
AI summary
One dither mask having a highest spacial frequency is selected from a plurality of dither masks. Next, a granularity is obtained with reference to a table based on the selected dither mask and an ejection amount level per area. Moreover, a difference in granularity between adjacent areas is calculated with respect to all of the areas. A maximum value is obtained out of the obtained differences in granularity, and then, the maximum difference in granularity is compared with a determination threshold. When the maximum difference in granularity is the threshold or greater, it is determined whether or not a dither mask having a spacial frequency lower than that of the selected dither mask is stored in a memory. When there are dither masks having lower spacial frequencies, a dither mask having a spacial frequency lower by one level than that of the selected dither mask is selected.