Defocus Estimation for Non-Planar Scanning
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional document scanners face issues with geometric distortion and defocus blur when scanning non-planar objects like bound books due to varying defocus distances and illumination variations, leading to suboptimal image quality and increased complexity in image processing.
Innovation Solution
The method involves scanning a non-planar object at two different focal planes with a predetermined distance between them, estimating the out-of-focus distance using the differences in the scanned images, and applying inverse filtering for deblurring and geometric distortion correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional document scanner optical systems are used to scan non-planar objects, then the scanning process is simple and fast, but geometric distortion and defocus blur occur in regions outside the depth of field
Solution Approach 1:
The patent applies dynamics by making the focal plane adjustable and movable to adapt to different defocus distances across non-planar objects. The optical system dynamically adjusts the focal plane position during scanning to maintain focus on surfaces at varying distances from the platen, thereby resolving the contradiction between fast scanning and high image quality.
2Manufacturing precision
If the platen is modified with a sloping edge portion to improve contact with bound books, then defocus blur is reduced, but magnification range is limited and split scan capability is lost
Solution Approach 1:
The patent applies parameter changes by adjusting the focal plane position parameter dynamically during scanning. Instead of modifying the platen geometry, the system changes the optical focal plane parameter to match the defocus distance of non-planar surfaces, thereby maintaining defocus correction while preserving full magnification range and split scan capability.
3Measurement precision
If infrared distance sensors or profile detectors are added to measure defocus distance, then defocus measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies self-service by using the scanned image data itself to determine the defocus distance. The system analyzes the scanned images to identify features and calculate defocus distances without requiring external sensors or detectors. This self-determination approach maintains measurement precision while avoiding additional hardware complexity and cost.
4Manufacturing precision
If fixed or time-varying image restoration filters with pre-selected coefficients are used, then defocus restoration is achieved, but image processing complexity increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the restoration filter coefficients based on the measured defocus distance for each image region. Instead of using fixed pre-selected coefficients, the system changes the filter parameters adaptively to match the local defocus conditions, achieving high restoration quality while maintaining processing efficiency through parameter optimization.
Data Source
AI summary
A method for determining local defocus distance in a scanned image of a non-planar original object is provided comprising scanning at least a portion of the non-planar original object to produce first scanned image data at a first focal plane and scanning same the at least a portion of the non-planar original object to produce at least second scanned image data at a second focal plane. The first scanned image data is different from the second scanned image data wherein a distance between the first focal plane and the second focal plane is a predetermined quantity. The method further comprises estimating an out-of-focus distance of the object from the first and the second scanned image data.