Roll-off Correction in Digital Image Processing
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Solution Overview
Problem
Digital imaging systems face challenges in achieving high image quality due to inherent monochrome image sensors, spatial variations in image attributes, and defects such as dark or bright spots, which result in unacceptable image quality, especially in low-cost and compact camera applications.
Innovation Solution
A system and method for processing digital images that corrects for roll-off variability by determining each pixel's roll-off contour and adjusting its luminance, color, and modulation transfer function, using sets of linear segments to define contours for efficient computation, and replaces bad pixels based on comparisons with neighboring pixels to improve image quality and reduce sensor defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If low-cost and small size optics are used, then cost and compactness are improved, but spatial variations in image attributes and quality occur
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction factors for luminance, color, and MTF roll-off in lookup tables before image processing. These correction factors are determined based on the specific optical system's characteristics and are applied during image processing to compensate for spatial variations, thereby resolving the quality uniformity issue without requiring expensive optics
Solution Approach 2:
The patent changes parameters by adjusting luminance, color, and MTF values pixel-by-pixel based on their position in the image. The system modifies these optical parameters using correction factors derived from the optical system's point spread function, enabling compensation for spatial variations introduced by low-cost optics
2Volume of moving object
If low-cost and small size optics are used, then device size is reduced, but image quality variability increases
Solution Approach 1:
The system performs preliminary characterization of the optical system to determine the point spread function and generates correction lookup tables in advance. This preliminary action enables the compact camera to compensate for its optical limitations through digital processing, maintaining image quality uniformity without increasing physical size
Solution Approach 2:
The patent replaces mechanical/optical solutions with digital signal processing. Instead of using larger, more precise optics to achieve uniform image quality, the system uses computational methods including FFT-based convolution and pixel-by-pixel correction to achieve the same goal in a compact form factor
3Device complexity
If pixel defects are not corrected, then processing complexity is reduced, but image quality becomes unacceptable
Solution Approach 1:
The patent extracts and identifies defective pixels through statistical analysis of pixel values and their neighbors. Bad pixels are detected by comparing pixel intensities against expected distributions and neighboring pixel values, then replaced using interpolation from surrounding good pixels, thereby removing the harmful effect of defects while maintaining acceptable processing complexity
Solution Approach 2:
The system uses the majority of good pixels to serve and replace the defective minority. By using statistical methods that rely on the self-consistency of good pixel distributions and neighboring pixel relationships, the system enables automatic defect detection and correction without requiring external calibration or complex processing
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively improves image quality by reducing defects and variability, enhancing luminance, color accuracy, and modulation transfer function, resulting in better image resolution and color representation while maintaining detail and reducing computational resources.
Implementation Method 1
When subjected to light, the image sensor converts incident photons to electrons
Data Source
AI summary
A system and method is provided for processing a digital image. The system and method processes image data by correcting for roll-off variability in the digital image. The system and method corrects for roll-off in image data by determining for each pixel a roll-off contour in which the pixel resides and adjusting that pixel based upon its roll-off contour, which in turn, depends upon its location on the image plane.