Iris Capture Camera with Dynamic Focus Sweep and Range Finder
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Solution Overview
Problem
Iris recognition systems face challenges in capturing focused near-infrared iris images due to the short depth of field and inefficiencies in NIR illumination, making it difficult to accurately focus on the iris, especially with dark eyes, as autofocus mechanisms are ineffective.
Innovation Solution
A digital camera system that dynamically changes focus points in a sequence with overlapping depths of field, using a mechanical or electronic shutter and synchronized illumination, to ensure at least one well-focused image is captured, employing a range finder for precise positioning and optimizing focus and illumination settings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If near-infrared illumination is used to capture iris images, then the ability to see through iris coloration is improved, but the sensor efficiency decreases and more illumination is required
Solution Approach 1:
The system pre-determines the subject's position using a range finder before capturing the iris image. This preliminary positioning allows the camera to pre-adjust focus and illumination settings optimized for NIR imaging, compensating for reduced sensor efficiency by ensuring maximum light capture at the correct focal point before the actual image capture occurs.
Solution Approach 2:
The system dynamically changes camera parameters including focus position and illumination intensity based on the predetermined subject position. By adjusting these parameters optimally for NIR imaging conditions, the system maximizes the already-limited NIR sensor efficiency while maintaining the ability to penetrate iris coloration.
2Illumination intensity
If camera aperture is set for intense illumination, then illumination capability is improved, but depth of field becomes short and focusing becomes difficult
Solution Approach 1:
The range finder provides preliminary position information that allows the system to pre-calculate the optimal focus position before capturing the image. This preliminary action enables precise focusing despite the shallow depth of field created by the wide aperture setting, as the focus is predetermined based on accurate range measurement rather than relying on autofocus mechanisms.
Solution Approach 2:
The system introduces an intermediary positioning system (range finder) that mediates between the wide aperture setting and the need for precise focusing. The range finder acts as an independent measurement tool that provides accurate distance information, allowing the camera to set focus precisely without being constrained by the limited depth of field of the wide aperture lens.
3Ease of operation
If autofocus mechanism is used, then ease of operation is improved, but reliability decreases because iris position varies within operating range
Solution Approach 1:
The system replaces the unreliable autofocus mechanism with an intermediary active ranging system. The range finder serves as an intermediary that directly measures distance to the subject, providing reliable position information independent of the camera's focus mechanism. This intermediary measurement system eliminates the variability and unreliability of autofocus when the iris position changes within the operating range.
Solution Approach 2:
The system substitutes the mechanical autofocus system with an electronic active ranging system. Instead of relying on mechanical focus adjustment mechanisms that struggle with varying iris positions, the system uses electronic range finding to determine position and then electronically controls focus settings, achieving both ease of operation and reliability through electronic substitution of mechanical autofocus.
4Reliability
If depth of field is increased, then focusing reliability is improved, but illumination intensity must be reduced
Solution Approach 1:
The system performs preliminary position determination using the range finder, allowing it to capture the image at the optimally determined focus position with maximum illumination intensity. By knowing the exact position in advance, the system can use a wide aperture for intense illumination without sacrificing focusing reliability, as the focus is predetermined rather than relying on increased depth of field.
Data Source
AI summary
According to one example embodiment, a process and system include a camera used to capture a sequence of illuminated images of an subject, wherein the images are stored in frames. The focus point is changed for each image captured so that the focus point sweeps from a far to a near end of a sweep range, in discrete steps or continuous motion, so that successive images have slightly overlapping depths of field. The sweep range and overlapping depths of field provide that at least one image is well focused on the iris of the eye of the subject. In one other example embodiment, one or more of the images are illumined with a illumination fired for a respective captured image. In another embodiment, the sweep range is determined at least in part using a range finder or is otherwise controlled to determine a position of the subject so that the sweep range starts and stops a desired distance in front of and behind the subject, respectively.