Multi-pass Image Processing Dot Overlap Control
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Solution Overview
Problem
Existing multi-pass printing methods face challenges in maintaining image density uniformity due to printing position displacement between planes, leading to density fluctuations and graininess issues, as they struggle to balance dot overlap rates for robustness and quality.
Innovation Solution
The method involves controlling the dot overlap rate by performing quantization processing on multi-valued image data for each scan based on threshold values specific to each scan, using error diffusion matrices and threshold tables to adjust binary data generation for each nozzle array, ensuring balanced dot distribution across scans and nozzle arrays.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multi-pass printing is performed with complementary mask patterns to ensure complete coverage, then image density uniformity deteriorates due to printing position displacement between planes, but using non-complementary patterns reduces coverage completeness
Solution Approach 1:
The patent changes the parameter of mask pattern complementarity from complete complementarity to partial complementarity. By controlling the dot overlap rate to be within a specific range (5-50%) rather than enforcing complete coverage, the system achieves robustness against printing position displacement while maintaining acceptable image quality. This parameter adjustment resolves the contradiction between coverage completeness and density uniformity.
Solution Approach 2:
The patent applies partial action by not requiring complete coverage of all pixels across all printing planes. Instead of ensuring every pixel is covered by at least one dot (excessive action), the system allows some pixels to remain uncovered while controlling the overall dot overlap rate. This partial approach reduces sensitivity to printing position errors while maintaining sufficient image density.
2Manufacturing precision
If binary image data is divided using complementary masks for each printing scan, then complete image coverage is achieved, but density fluctuations and graininess occur due to printing position displacement
Solution Approach 1:
The patent changes the parameter of dot overlap control from binary (covered/not covered) to a continuous range (5-50% overlap rate). By introducing this intermediate parameter range, the system achieves a balance between coverage completeness and reduction of density fluctuations caused by printing position displacement, thereby reducing graininess while maintaining robustness.
Solution Approach 2:
The patent uses multiple printing planes (copies of the same image data processed through different masks) to achieve robustness. By distributing the printing across multiple planes with controlled overlap, the system creates redundant coverage that compensates for printing position displacement, reducing density fluctuations and graininess while maintaining complete image coverage.
3Reliability
If dot overlap rate is increased to improve robustness against printing position displacement, then density uniformity improves, but graininess increases
Solution Approach 1:
The patent optimizes the dot overlap rate parameter to a specific range (5-50%) that balances robustness and graininess. This parameter optimization resolves the contradiction by identifying the optimal intermediate value range where sufficient overlap provides robustness against position displacement while avoiding excessive overlap that causes visible graininess in the printed image.
Data Source
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AI summary
An image processing apparatus that outputs a high-quality image having excellent robustness and reduced graininess by using a multi-pass printing method that performs printing in pixel areas of a printing medium based on a plurality of multi-valued image data that correspond to a plurality of relative movements. To accomplish this, the image processing apparatus executes quantization processing of second multi-valued image data that corresponds to a second relative movement of a plurality of relative movements based on first multi-valued image data that corresponds to a first relative movement of the plurality of relative movements, and executes quantization processing of the first multi-valued image data based on the second multi-valued image data. This makes it possible to output a high-quality image having excellent robustness and reduced graininess by controlling the overlap rate of dots that are printed by the first relative movement and the dots that are printed by the second relative movement.