Defective Pixel Correction in Contact Image Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing image processing methods for scanner devices, particularly those using contact image sensors (CIS), struggle to accurately estimate and supplement pixel values for missing or incorrect pixels, especially in halftone areas with high screen ruling, leading to discontinuities and reduced image quality due to errors in sensor construction and pattern matching limitations.
Innovation Solution
An image processing apparatus that determines whether a pixel value is periodic or non-periodic, using a combination of pattern matching and interpolation methods to generate candidate pixel values, and updates neighboring pixel values to ensure continuity, thereby accurately supplementing defective pixels and reducing discontinuities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pattern matching method is used to estimate pixel value of target pixel in halftone area, then pixel value can be estimated using similar pattern, but the selected similar pattern may not always include optimum pixel value because a pattern slightly different from standard pattern and a pattern with small part largely different are not discriminated
Solution Approach 1:
The patent applies local quality by dividing the image into different processing regions based on periodicity detection. For periodic regions (halftone areas), pattern matching is used with periodicity-aware processing. For non-periodic regions, interpolation methods are used. This localized approach ensures each region receives the most appropriate processing, improving both accuracy and reliability of pixel value estimation.
Solution Approach 2:
The patent changes the processing parameter based on the detected periodicity of the image region. When periodicity is detected, the system switches to pattern matching mode with periodicity constraints. When no periodicity is detected, it switches to interpolation mode. This dynamic parameter change allows the system to adapt to different image characteristics, resolving the contradiction between accuracy and reliability.
2Ease of operation
If interpolation method using linear interpolation is used, then pixel value can be interpolated in area with small gradation variation, but it is not adaptable for area with large gradation variation such as halftone area
Solution Approach 1:
The patent implements dynamics by making the processing method adaptive rather than static. The system dynamically detects periodicity in the image and automatically selects the appropriate processing method (pattern matching for periodic areas, interpolation for non-periodic areas). This dynamic adaptation allows the system to handle both simple and complex image regions effectively, resolving the contradiction between operational simplicity and method versatility.
3Measurement precision
If polynomial interpolation or spline interpolation is used, then pixel value can be estimated with high accuracy where sampling period is short, but for halftone image the sampling period may be ambiguous with respect to variation period and therefore difficult to estimate accurate pixel value
Solution Approach 1:
The patent applies preliminary action by performing periodicity detection before executing the pixel value estimation. This preliminary step identifies whether the image region has periodic characteristics, allowing the system to pre-select the appropriate processing method. By detecting periodicity in advance, the system avoids the difficulty of determining sampling periods in halftone areas and ensures accurate pixel value estimation from the outset.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided is an image processing apparatus including a periodicity determining unit that determines whether a determination area including a target defective pixel is a periodicity area, a first pixel value generating unit that generates a pixel value by a first supplementing method, a second pixel value generating unit that generates a pixel value by a pixel second supplementing method, a control unit that determines which of the first pixel value generating unit and the second pixel value generating unit is to be used based on the determination by the periodicity determining unit, a pixel value supplementing unit that inserts the pixel value generated by the pixel value generating unit determined to be adopted, and a pixel value updating unit that updates pixel values of neighboring pixels of the defective pixel.