Line Sensor Luminance Correction for Glossy Document Specular Reflection
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Solution Overview
Problem
Current image processing methods for correcting shadows in saddle-stitch bound documents, particularly those with glossy paper, fail to accurately address luminance abnormalities caused by specular reflection, leading to undesirable corrections due to varying surface reflection characteristics and document curvatures.
Innovation Solution
An image processing method involving a line sensor to detect and correct the luminance of regions affected by specular reflection, using a determination unit to assess document placement and a correction unit to adjust image luminance based on calculated shadow and specular reflection ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional shadow correction methods are applied to glossy paper documents, then general luminance correction is performed, but specular reflection causes inaccurate correction and undesirable results
Solution Approach 1:
The patent segments the document surface into planar portions and curved portions, and further segments the curved portions into specular reflection regions and non-specular reflection regions based on reflection characteristics. This segmentation allows different correction strategies to be applied to different regions, improving both accuracy and reliability of luminance correction.
Solution Approach 2:
The patent applies different correction methods to different regions of the document. Specifically, specular reflection regions are identified and handled separately from non-specular regions using local reflection characteristic analysis. This local quality approach ensures that correction is tailored to the specific optical properties of each region, resolving the contradiction between accuracy and reliability.
2Object-affected harmful factors
If pressure is applied to prevent document floating from platen, then shadow problems are avoided, but damage to the copied document may result
Solution Approach 1:
The patent replaces the mechanical approach of applying pressure to the document with an optical and computational approach. By analyzing reflection characteristics and identifying specular reflection regions, the system corrects shadows through image processing rather than physical contact, thus eliminating the risk of document damage while still addressing shadow problems.
3Device complexity
If specular reflection regions are not specifically identified, then processing is simpler, but correction accuracy deteriorates due to varying surface reflection characteristics
Solution Approach 1:
The patent performs preliminary identification of specular reflection regions by analyzing reflection characteristics before applying correction. This preliminary action involves detecting regions with specular reflection properties and marking them for special handling, which enables subsequent correction to be more accurate without excessively increasing overall processing complexity.
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 effectively corrects luminance abnormalities in saddle-stitch bound documents, improving image quality by accurately accounting for specular reflection and document curvature, even with glossy paper, thereby enhancing the readability of images.
Implementation Method 1
a line sensor having a light receiving element which receives light reflected from a document
Implementation Method 2
an image sensor 2405 such as a CCD sensor which then performs photoelectric conversion
Implementation Method 3
specular reflection light 2407, which is illumination light undergoing specular reflection on the document surface
Data Source
AI summary
An image processing apparatus determines a direction of document placement relative to a scanning direction based on a direction of a shadow region in an input image when a line sensor having a light receiving element performs a scan and an image read from a book document by a reading apparatus is input. When the direction of the binding portion of the document is determined to be along a longitudinal direction of the line sensor, an image of a region read by the light receiving element of the line sensor from reflected light undergoing specular reflection from the document is detected based on the amount of variation in luminance between adjacent pixels in the read image of the book document. Luminance of the image corresponding to the region is corrected.