Threshold Value Matrix Generation for Image Forming Apparatus
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Solution Overview
Problem
Conventional image forming apparatuses face challenges in producing high-quality images with low resolution, resulting in limited gradations and rough patterns due to regular halftone arrangements, which are not visually appealing and lack high frequency components.
Innovation Solution
An image forming apparatus that generates a threshold value matrix by determining the arrangement of standard dots, dividing pixels into halftones, and establishing a priority order for gradations, allowing for the conversion of M-level gradation images to N-level gradation images using a FM screen of a cluster type, thereby improving image quality and reducing pattern roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a regular production order between halftones is used according to Bayer arrangement, then the halftones are distributed uniformly in space and the arrangement order becomes the highest frequency, but the pattern looks rough and the low frequency component is not eliminated
Solution Approach 1:
The patent changes the parameter of production order from regular Bayer arrangement to blue noise-based arrangement. This parameter change transforms the ordering criterion from spatial regularity to frequency-based distribution, eliminating low frequency components while maintaining uniform spatial distribution of halftones.
Solution Approach 2:
The patent substitutes the mechanical regular ordering system (Bayer arrangement) with a noise-based system (blue noise). This replacement uses the statistical properties of blue noise to achieve uniform distribution while eliminating the harmful regularity that causes rough patterns.
2Device complexity
If the printing apparatus has low resolution (600 DPI), then the device complexity is reduced, but only limited gradations (19 gradations) can be realized with one halftone
Solution Approach 1:
The patent divides the image into multiple halftones (4×4=16 halftones) and assigns different production orders to each halftone based on blue noise properties. This segmentation allows the system to achieve 304 gradations (16×19) using low-resolution printing, effectively multiplying the gradation capability without increasing physical resolution.
Solution Approach 2:
The patent adds a new dimension to the halftone arrangement by introducing blue noise-based ordering that eliminates low frequency components. This additional dimensional control over the arrangement pattern enables better gradation representation and reduces pattern visibility, compensating for the limited physical resolution.
3Object-generated harmful factors
If blue noise is used for determining production order, then the low frequency component is eliminated and the pattern becomes more uniform, but the device complexity increases due to the need for blue noise generation and processing
Solution Approach 1:
The patent performs preliminary generation of the threshold value matrix using blue noise-based production order before actual image processing. By pre-computing the arrangement pattern and storing it in a lookup table, the system eliminates low frequency components in advance, reducing pattern visibility without adding complexity during real-time operation.
Data Source
AI summary
An image forming apparatus for depicting a gradation image through halftones includes a threshold value generating unit for generating a threshold value matrix, and a comparison unit for converting the gradation image. The threshold value generating unit determines an order of gradations of pixels in halftones. The threshold value generating unit determines an order of standard dots. Further, the threshold value generating unit is configured to determine a priority order of gradations between the halftones. The threshold value generating unit further determines an order of the threshold values of the gradations of all of the pixels according to the order of the gradations of the pixels contained in the halftones and the priority order of the gradations between the halftones, so that the threshold value generating unit generates the threshold value matrix.