Image Processing Apparatus Moire Suppression and Sharpness
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Solution Overview
Problem
Existing halftone processing methods struggle to maintain image sharpness while effectively suppressing moire interference between AM screens and high-frequency components, often resulting in incomplete extraction and compensation of high-frequency components.
Innovation Solution
An image processing apparatus that generates low-frequency and high-frequency images, performs AM screen processing on the low-frequency image, adds the high-frequency image, and corrects pixel values within a specified gradation range to suppress moire and maintain high-frequency reproducibility, using a combination of low-pass and high-pass filters and gradation limiting units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low-pass filter is applied to remove high-frequency components before AM screen processing, then moire interference is suppressed, but image sharpness deteriorates due to blunted edge portions
Solution Approach 1:
The image is segmented into low-frequency components (for moire suppression) and high-frequency components (for sharpness preservation). The low-pass filter processes only the low-frequency component image, while the high-frequency component image is processed separately and then combined, allowing selective application of filtering to resolve the contradiction between moire suppression and sharpness maintenance.
Solution Approach 2:
The high-frequency component image acts as an intermediary that carries the sharpness information. By extracting high-frequency components from the original image, applying the low-pass filter only to the low-frequency component, and then adding the high-frequency component image back to the processed low-frequency image, the intermediary preserves edge sharpness while allowing moire suppression in the main processing path.
2Object-affected harmful factors
If a low-pass filter sufficient to remove high-frequency components is applied, then moire is suppressed, but edge portions become blunted
Solution Approach 1:
The image processing is segmented into two parallel paths: one for low-frequency components where the low-pass filter is applied to suppress moire, and another for high-frequency components that are extracted and preserved separately. This segmentation allows the filter to suppress moire without affecting edge sharpness, as the high-frequency edge information is restored through addition of the preserved high-frequency component image.
Solution Approach 2:
The high-frequency component image is extracted and preserved in advance before the low-pass filtering operation. This preliminary action ensures that the sharpness-critical high-frequency information is protected from the blunting effect of the low-pass filter, and can be restored afterward to maintain edge sharpness while still achieving moire suppression.
3Manufacturing precision
If high-frequency components are extracted from the image subjected to AM screen processing, then sharpness can be restored, but harmonic components of halftone dots interfere with accurate extraction
Solution Approach 1:
The high-frequency component image is extracted from the original input image before AM screen processing is applied. This preliminary extraction prevents the introduction of harmonic components from the halftone dots, ensuring that the high-frequency information remains pure and free from interference. The extracted high-frequency component image is then added to the AM-screen-processed low-frequency image to achieve sharpness enhancement without contamination by halftone harmonics.
Data Source
AI summary
An image processing apparatus according to an embodiment of the present invention includes: a first generation unit that generates a low-frequency image by extracting a low-frequency component from an input image; a second generation unit that generates a high-frequency image by extracting a high-frequency component from the input image; a screen processing unit that generates an AM screen image by performing AM screen processing on the low-frequency image; an addition processing unit that generates an added image by adding the high-frequency image to the AM screen image; and a correction unit that corrects the added image.