Dither Matrix Phase Alignment for Print Density Uniformity
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Solution Overview
Problem
Density unevenness in print images caused by misalignment between head shading correction based on absolute position correspondence and dither matrix quantization using relative position correspondence, leading to increased density variations in printouts.
Innovation Solution
An image processing apparatus and method that determines correction parameters for unit areas in printing element arrays, applying these parameters to correct image data and quantize it using a dither matrix, ensuring the phase of the dither matrix matches between the test pattern and image data, thereby reducing density unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If head shading correction is performed based on absolute position correspondence while dither matrix quantization uses relative position correspondence, then correction parameters can be determined for each unit area, but density unevenness occurs due to misalignment between correction application positions and quantization positions
Solution Approach 1:
The patent divides the print head array into multiple unit areas and determines correction parameters for each unit area based on local density measurements. This local quality approach allows the correction to account for spatial variations in print characteristics across different regions of the print head, improving both measurement precision and print density uniformity by addressing local rather than global characteristics alone.
Solution Approach 2:
The patent creates a correspondence relationship between test pattern positions and image data positions by copying the same dither matrix phase to both test pattern generation and image data quantization. This copying ensures that the quantization process in actual printing replicates the conditions under which correction parameters were measured, eliminating misalignment between correction application and quantization positions.
2Productivity
If dither matrix quantization is used for test pattern printing in HS analysis, then quantization can be performed efficiently, but the number of dots varies according to pixel positions causing density unevenness
Solution Approach 1:
The patent changes the dither matrix phase parameter to align with the unit area division used in HS correction. By adjusting the phase parameter of the dither matrix to match the correction grid, the quantization process produces consistent dot patterns across unit areas, maintaining processing efficiency while achieving density uniformity that corresponds to the correction parameter structure.
3Adaptability or versatility
If the dither matrix phase differs between test pattern quantization and image data quantization, then processing can be performed independently, but misalignment occurs leading to increased density variations
Solution Approach 1:
The patent establishes a universal dither matrix phase that serves both test pattern generation and image data quantization. This universal phase setting allows the same quantization parameters to be used in both HS analysis and actual printing, ensuring that the correction parameters measured during analysis are directly applicable to printing operations, thereby maintaining density uniformity while enabling independent processing of test patterns and image data.
Data Source
AI summary
When an input image is shifted by 640 pixels from a test pattern with reference to the position of a nozzle, the remainder is obtained by dividing 640 pixels by pixels of the dither matrix in an x direction. For example, when the size of the dither matrix in the x direction is 256 pixels, the dither matrix is shifted by 128 pixels in a direction reverse to the x direction. In this manner, the phase of the dither matrix at the time of the quantization during test pattern printing matches the phase of the dither matrix at the time of the quantization during input image printing. Consequently, unevenness of the dither matrix at a position N becomes the same in both of the test pattern and the input image. The HS correction to density unevenness caused by the unevenness of the dither matrix becomes suitable for the input image.