Iris Image Definition Estimation Using Corneal Reflection Astigmatism
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Solution Overview
Problem
Current iris recognition systems face challenges in determining the resolution and direction of focus adjustment for high-definition iris images, particularly due to the shallow depth of field in telephoto lenses and the impact of user head movements, leading to inefficiencies and errors in auto-focusing processes.
Innovation Solution
The system employs a non-coaxial light source to produce astigmatism in the corneal reflection, allowing for the use of a single image to determine both the resolution and direction of focus adjustment by analyzing the shape and size of the composite glint area formed by meridional and sagittal virtual images, enabling fast and accurate auto-focusing without additional equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a telephoto lens with a long focal length is used to obtain high resolution iris pattern, then the resolution of iris image is improved, but the depth of field becomes very shallow making focus adjustment difficult
Solution Approach 1:
The patent replaces the traditional mechanical auto-focusing system with an optical-based astigmatism detection method. By analyzing the shape of the corneal reflection (glint area) formed by a non-coaxial light source, the system determines focus status and adjustment direction without mechanical movement or complex calculations, thereby simplifying the focusing mechanism while maintaining high resolution capability
Solution Approach 2:
The patent introduces the corneal reflection (glint area) as an intermediary indicator to assess focus status. Instead of directly measuring iris image quality, the system uses the easily detectable glint area shape as a proxy, which correlates with focus accuracy and provides clear directional feedback for adjustment
2Measurement precision
If auto-focusing or guided focusing mechanism is used to produce high resolution image, then the resolution of iris image is improved, but the time required for focus determination and adjustment increases
Solution Approach 1:
The patent extracts the focus assessment information from the iris image itself by analyzing the corneal reflection pattern. This extracted glint area shape provides direct focus status information without requiring full iris image processing, significantly reducing computational time while maintaining focus accuracy
Solution Approach 2:
The patent performs preliminary focus assessment by detecting the glint area shape before final image capture. This preliminary detection provides immediate feedback on focus status and adjustment direction, allowing for rapid correction without waiting for full image processing
3Measurement precision
If intensity of high frequency components is used to determine focus measure, then the resolution estimation is achieved, but the calculation workload is extensive preventing real-time processing
Solution Approach 1:
The patent substitutes complex computational analysis of high frequency components with a simpler geometric analysis of the glint area shape. By measuring the aspect ratio of the corneal reflection instead of processing frequency spectra, the system achieves real-time focus assessment with minimal computational load
Solution Approach 2:
The patent changes the measurement parameter from frequency domain (intensity of high frequency components) to spatial domain (shape of glint area). This parameter transformation simplifies the calculation while preserving the ability to determine focus status and adjustment direction
4Productivity
If near coaxial light source is used to reduce calculation time, then the processing speed is improved, but the direction of focus adjustment cannot be determined when iris pattern is close to focus distance
Solution Approach 1:
The patent employs an asymmetric non-coaxial light source configuration where the light source is positioned at an angle to the optical axis. This asymmetry creates an asymmetric glint area shape that encodes directional information, allowing the system to determine both focus status and adjustment direction even when the iris is near the focal plane
5Measurement precision
If multiple trials are conducted to explore focus direction when iris is close to focus distance, then the accuracy of focus adjustment is improved, but the time required for image acquisition increases dramatically
Solution Approach 1:
The patent uses the glint area shape as an intermediary indicator that provides immediate directional feedback without requiring multiple trial images. The asymmetric shape directly indicates which direction focus adjustment should proceed, eliminating the need for iterative exploration and reducing acquisition time
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 simplifies the calculation for high-definition iris image acquisition, reduces user training requirements, and minimizes errors in focus adjustment, achieving real-time processing and cost-effective iris recognition.
Implementation Method 1
uses the astigmatism of the corneal reflection of a non-coaxial source to produce two virtual images of the light source on the meridional and sagittal image planes
Implementation Method 2
the corneal reflection of a non-coaxial light source
Data Source
AI summary
An iris image definition estimation system using the astigmatism of the corneal reflection of a non-coaxial light source to assess both the resolution of the iris patterns and the direction of focus adjustment. The corneal reflection results in two virtual images on the meridional and the sagittal planes. These virtual images are formed behind the cornea and close to the iris. Yet, both are projected onto the same location and result in a composite glint area. In addition, the shape of the glint area of a non-coaxial light source varies with different camera focus settings. Furthermore, due to the high intensity of the glint area, the shape can be easily observed, and the size and the shape of the glint area can be used to determine the resolution of the iris image and the direction of focus adjustment, respectively.