Shading Correction for Image Sensors Using Encoder Pulses
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Solution Overview
Problem
Existing image reading technologies using DC motors for image sensors face challenges in accurately correcting shading data due to fluctuations in motor speed, leading to incomplete correction of dark current effects in singular pixels, resulting in vertical streaks in scanned images.
Innovation Solution
An image reading apparatus that uses a motor-driven movement unit and an output unit to accumulate light-receiving signals for each color channel independently, with a correction unit applying specific correction values to each color channel based on encoder pulses, allowing for precise shading correction across varying accumulation times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If shading data is corrected by average data for each line, then processing complexity is reduced, but correction completeness deteriorates due to inability to correct singular pixel dark current
Solution Approach 1:
The patent segments the correction process into two distinct parts: (1) correction of average dark current using line-average data, and (2) correction of singular pixel dark current using per-pixel data. This segmentation allows the system to handle both types of correction efficiently without excessive complexity while achieving complete correction.
Solution Approach 2:
The patent applies different correction strategies to different types of pixels based on their characteristics. Average pixels are corrected using line-average data, while singular pixels with abnormal dark current are corrected using their own specific data. This local quality approach ensures each pixel type receives the most appropriate correction method.
2Ease of operation
If accumulation time fluctuates due to DC motor speed variation, then motor silentness and smooth operation are improved, but shading data accuracy deteriorates due to dark current and white level changes
Solution Approach 1:
The patent performs preliminary shading data acquisition at multiple different accumulation times before actual image reading. By pre-acquiring shading data corresponding to various accumulation time conditions, the system can later select the appropriate shading data that matches the actual accumulation time, thereby compensating for accuracy deterioration caused by DC motor speed variations.
Solution Approach 2:
The patent changes the accumulation time parameter during shading data acquisition to capture shading characteristics under different conditions. By acquiring shading data at multiple accumulation times and selecting the one that matches the actual reading conditions, the system maintains shading data accuracy despite motor speed fluctuations.
3Manufacturing precision
If per-pixel shading correction is implemented, then correction completeness is improved, but memory requirement and processing time increase excessively
Solution Approach 1:
The patent segments correction data storage into two categories: line-average shading data that can be shared across all pixels, and minimal per-pixel correction values only for singular pixels. This segmentation dramatically reduces memory requirements compared to storing full per-pixel correction data for all pixels, while still achieving complete correction.
Solution Approach 2:
The patent applies per-pixel correction only where necessary (for singular pixels with abnormal dark current) rather than uniformly to all pixels. This partial action approach maintains correction completeness for problematic pixels while avoiding the excessive memory and processing requirements of universal per-pixel correction.
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
This approach enables complete correction of both average and singular pixel dark current effects, eliminating vertical streaks and improving image quality without requiring excessive memory or processing time.
Implementation Method 1
an image sensor (101) to read a document
Data Source
AI summary
An image reading apparatus according to an embodiment of the present invention includes: an image sensor to read a document; a movement unit configured to relatively move the document and the image sensor by using a motor as a drive source; an output unit configured to output data of a plurality of colors based on accumulated light-receiving signals by accumulating the light-receiving signals from the image sensor for each color in order for each line in a direction of the movement based on an encoder pulse output from an encoder in accordance with rotation of the motor; and a correction unit configured to perform shading correction for each piece of data of the plurality of colors output by the output unit by using a correction value to correct influence on data of the plurality of colors due to a dark current in the image sensor based on shading data.