Threshold Matrix Generation for Inkjet Graininess Reduction
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Solution Overview
Problem
Inkjet image recording apparatuses face challenges in reducing graininess during high-speed image recording, particularly in highlight areas, due to misaligned ink droplet landing positions, which can lead to increased graininess and moire patterns.
Innovation Solution
A threshold matrix generation method that sets specific writing and non-writing elements in a checkerboard pattern within a matrix space, determining threshold values based on occurrence numbers to optimize dot placement and reduce graininess, effectively employing pseudo AM screening to minimize misalignment impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If FM screening is used for high-speed image recording, then recording speed is improved, but graininess increases due to disordered ink landing positions
Solution Approach 1:
The patent applies preliminary action by pre-generating a threshold matrix with predetermined threshold values at each position before the actual image recording process. This threshold matrix is used to determine ink ejection positions in advance, ensuring that even during high-speed recording, the ink droplets land at predetermined positions that prevent graininess. The threshold matrix generation and storage occur beforehand, allowing the recording apparatus to simply reference pre-calculated values during high-speed operation.
2Manufacturing precision
If AM screening is used to reduce graininess, then graininess is reduced, but moire patterns occur due to interference between halftone dot periodicity and nozzle arrangement periodicity
Solution Approach 1:
The patent applies local quality by assigning different threshold values to different positions within the threshold matrix, creating local variations in dot placement characteristics. Each position in the matrix has a specifically tailored threshold value that accounts for its unique location relative to nozzles and other positions, thereby preventing regular periodic patterns that cause moire while still maintaining uniform graininess reduction across the entire image area.
Solution Approach 2:
The patent applies asymmetry by using an irregular, non-periodic arrangement of threshold values in the threshold matrix that does not align with the periodic nozzle arrangement. The threshold values are determined through a specific generation method that creates an asymmetric pattern, breaking the periodicity that would otherwise interfere with the regular nozzle spacing and cause moire patterns.
3Speed
If threshold matrix is generated for Nx speed writing, then high-speed recording capability is improved, but complexity of threshold matrix generation increases
Solution Approach 1:
The patent applies periodic action by making the threshold matrix repeatable across multiple writing cycles. The threshold matrix is generated with a specific size and pattern that can be repeatedly applied during Nx speed writing operations. This periodic structure allows the same threshold matrix to be used cyclically, simplifying the generation process compared to creating unique patterns for each writing cycle, while still achieving high-speed recording performance.
Data Source
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AI summary
In the generation of a threshold matrix for Nx speed writing, first and second areas are set, the first area being a cluster of a plurality of first partial areas substantially evenly distributed in a matrix space, and the second area being an area of the matrix space excluding the first area. Next, at least two writing elements in each of the first partial areas are allocated occurrence numbers and changed into determined elements. Then, at least one writing element in the second area is allocated an occurrence number and changed into a determined element. Thereafter, the other writing elements are allocated occurrence numbers and changed into determined elements. In accordance with the occurrence numbers, the threshold value of each writing element is determined to obtain a threshold matrix for Nx speed writing. This results in a reduction in the graininess of an image in a highlight area.