Image Reading Apparatus Shading Correction for Double-Sided Originals
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Solution Overview
Problem
Image reading apparatuses struggle with in-surface color irregularities and color differences between the front and reverse sides of double-sided originals during simultaneous reading, leading to density differences in monochrome and color copying, and require complex shading correction systems that increase manufacturing costs.
Innovation Solution
An image reading apparatus with a correction unit that uses reference originals with different density patches to adjust gain and offset values for each pixel, reducing density linearity characteristics and performing shading correction to match reading characteristics between the front and reverse sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If two image readers are provided to read both sides of an original during one-time conveyance, then productivity is improved, but reading position-dependent variation in light amount and front-side/reverse-side reading level differences occur
Solution Approach 1:
The patent applies preliminary action by performing shading correction before actual image reading. Reference white plates are read in advance to generate correction data that compensates for light amount variations and reading level differences between front and reverse sides, ensuring uniform reading characteristics are established prior to productivity-critical double-sided reading operations
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting gain and offset parameters based on readings from reference white plates. The correction unit modifies reading parameters (gain/offset) according to detected light amount variations and reading level differences, enabling adaptive compensation that maintains measurement precision while preserving the high productivity of simultaneous double-sided reading
2Reliability
If uniform gain adjustment is performed in the main scanning direction for shading correction, then reading characteristics matching is improved, but in-surface uniformity and density linearity characteristics are insufficient for security documents
Solution Approach 1:
The patent applies segmentation by dividing the correction approach into multiple independent components: reference white plate reading, gain calculation, offset calculation, and application to each pixel. This segmented correction process enables comprehensive adjustment of density linearity characteristics across different density patches, achieving both reading characteristics matching and in-surface uniformity required for security document verification
Solution Approach 2:
The patent extends correction from the traditional one-dimensional main scanning direction to a two-dimensional pixel space by applying gain and offset corrections to each pixel individually based on its density characteristics. This dimensional expansion enables precise control of density linearity across the entire image plane, achieving the in-surface uniformity and manufacturing precision needed for security documents while maintaining reading characteristics matching
3Measurement precision
If a system for shading correction and circuit for correcting shading correction data are added, then reading accuracy is improved, but device complexity and manufacturing costs increase
Solution Approach 1:
The patent implements self-service by enabling the image readers to perform their own shading correction using reference white plates read during normal operation. The correction unit within each reader calculates and applies its own gain and offset corrections autonomously, eliminating the need for complex external correction circuits and reducing device complexity while maintaining high reading accuracy
Solution Approach 2:
The patent uses reference white plates as simplified copies or proxies for actual documents to characterize and correct reading variations. By reading these reference plates and generating correction data, the system achieves accurate shading correction without requiring complex hardware, as the reference plates serve as surrogates that capture the essential optical path variations
Data Source
AI summary
An image reading apparatus which is capable of preventing images read from a double-sided original from suffering an in-surface color irregularity on each of images read from the respective opposite sides of a double-sided original and a color difference between the front and reverse. A CCD line sensor reads a front-side original image. An image processing ASIC calculates shading correction data for performing shading correction on original image data read from the original image by the CCD line sensor, based on read luminance values obtained by the CCD line sensor by reading a plurality of halftone gradation patches thereon on a correction chart. The shading correction data calculated by the image processing ASIC is corrected based on read luminance values associated, respectively, with at least two of the gradation patches.