Dither Mask Threshold Shift for Serial Inkjet Density Unevenness
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Solution Overview
Problem
Printing quality is deteriorated due to density unevenness in images produced by serial ink jet type printers, caused by position shifts during ink ejection, which can be exacerbated by variations in head scanning speed and distance between the printing head and medium.
Innovation Solution
A printing apparatus that uses a dither mask with threshold values shifted by a predetermined pixel in a specific direction, optimizing dot distribution to maintain noise characteristics with a peak on the high frequency side, thereby stabilizing dot dispersion and reducing graininess even with position shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If ink ejection is performed by a serial ink jet printing head, then printing speed can be increased, but position shift occurs causing density unevenness and printing quality deterioration
Solution Approach 1:
The patent applies preliminary action by pre-calculating and pre-positioning dots in the dot arrangement data to compensate for expected position shifts. The dot arrangement data is generated in advance with adjusted dot positions that account for the known position shift characteristics of the printing head, so that when printing occurs, the dots land at the correct target positions despite the mechanical position shift.
Solution Approach 2:
The patent changes parameters by adjusting dot positioning parameters in the dot arrangement data based on the printing head's position shift characteristics. The system modifies the dot position parameters to compensate for the position shift, transforming the dot arrangement parameters to achieve accurate print output despite the printing head's mechanical inaccuracies.
2Productivity
If dot formation is performed by multiple pixel groups in a common region, then printing efficiency is improved, but relative position shifts between pixel groups cause density unevenness
Solution Approach 1:
The patent applies local quality by treating different pixel groups with different dot arrangement strategies. The dot arrangement data is generated separately for each pixel group (first pixel group and second pixel group) with specific dot positions and arrangements tailored to each group's characteristics and position shift behavior, rather than using a uniform approach for all pixels.
Solution Approach 2:
The patent applies segmentation by dividing the printing process into separate pixel groups (first pixel group and second pixel group) with different printing conditions. Each pixel group's dot formation is controlled independently with separate dot arrangement data, allowing precise control over the relative positioning of dots from different pixel groups in the common region.
3Adaptability or versatility
If head scanning speed varies or distance between printing head and medium fluctuates, then printing adaptability is improved, but position shift fluctuation increases causing density unevenness
Solution Approach 1:
The patent applies dynamics by making the dot arrangement data adaptable to different printing conditions. The system generates dot arrangement data that can accommodate variations in scanning speed and head-to-medium distance by adjusting dot positions based on the actual printing conditions and position shift characteristics observed or measured during operation.
Data Source
AI summary
A printing apparatus which forms dots, according to dot data generated through comparison of a grayscale value of each of pixels with each of threshold values of a dither mask. The printing apparatus forms the dots through division into a plurality of pixel groups having different printing conditions and performs at least a part of the dot formation by the pixel groups in a common region. The dither mask has a second threshold value disposition, with respect to a first threshold value disposition which is each of dispositions of the respective threshold values set such that distribution of dots formed in the common region has noise characteristics having a peak on a high frequency side, in a case where a relative position of the dots between the pixel groups is formed in a target positional relationship which is a target in at least a part of a printing grayscale region.