Pixel Interpolation for Halftone Dot Image Artifact Reduction
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Solution Overview
Problem
Contact type linear image sensors generate missing pixels at connecting portions, leading to image quality deterioration due to step artifacts and stripe noise, especially in halftone dot images with fine periodic patterns, as existing interpolation methods are limited in handling two-dimensional patterns and cannot accurately determine intensity of multiple missing pixels.
Innovation Solution
A pixel interpolation apparatus using a weighting interpolation method that calculates pixel values for missing pixels based on neighborhood pixels, decomposes the image into frequency components, extracts halftone dot information, and adjusts the interpolated values using correction values to improve image quality by accounting for halftone dot regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a filter is used to interpolate missing pixels by employing peripheral pixels in the one dimensional direction, then step artifacts and stripe noise are reduced in line images and natural images, but unnatural stripes are generated in halftone dot images with fine periodic patterns
Solution Approach 1:
The patent transitions from one-dimensional interpolation (using only horizontal/vertical peripheral pixels) to two-dimensional interpolation (using diagonal and surrounding pixels). This dimensional expansion allows the interpolation to account for periodic patterns in halftone dot images, preventing unnatural stripe generation while maintaining effectiveness in reducing step artifacts and stripe noise in other image types.
Solution Approach 2:
The patent applies different interpolation strategies based on the local characteristics of the image. By detecting the type of image region (line image, natural image, or halftone dot image) and selecting appropriate reference pixels accordingly, the system optimizes interpolation quality for each specific case. This local adaptation prevents the generation of unnatural stripes in halftone dot regions while maintaining good performance in other regions.
2Device complexity
If reference pixels are limited in the one dimensional direction to determine average values for interpolation, then the interpolation method is simple to implement, but suitable interpolation corresponding to periodicity of two dimensional halftone dot image cannot be achieved
Solution Approach 1:
The patent extends the reference pixel selection from one dimension to two dimensions by incorporating diagonal pixels and surrounding pixels in the neighborhood. This two-dimensional reference region enables the interpolation to capture the periodicity characteristics of halftone dot images, significantly improving interpolation accuracy while maintaining reasonable implementation complexity through systematic pixel selection rules.
3Quantity of substance
If the reference region is widened in the one dimensional direction to include more pixels, then more data is available for interpolation, but reference pixels become distant from the missing pixel and relevance decreases
Solution Approach 1:
The patent emphasizes the use of pixels in the immediate neighborhood of the missing pixel, particularly diagonal pixels and pixels at specific distances. This localized approach ensures that reference pixels remain highly relevant to the missing pixel while still providing sufficient data for accurate interpolation. The method strategically selects a limited number of nearby pixels rather than widening the reference region, maintaining high relevance while having adequate reference data.
Data Source
AI summary
An embodiment has: weighting interpolation section for obtaining a pixel value for a missing pixel by a one-dimensional weighting interpolating method, using pixels in the vicinity of the missing pixel as reference pixels, and for generating a primarily interpolated image signal including the interpolated pixel value in place; frequency decomposition section for decomposing the primarily interpolated image signal into frequency components; halftone dot extraction sections for obtaining a halftone dot degree indicating a degree for the vicinity of the missing pixel to be in the halftone dot region, by using higher ones of these frequency components; correction value calculation section for calculating a correction value for the missing pixel, by using lower ones of these frequency components; and correction section for correcting the pixel value of the missing pixel in the primarily interpolated image signal using the correction value depending on the halftone dot degree.