Prototype Non-Contact Fingerprint Reader
A non-contact fingerprint sensor is the ultimate for a convenient, secure biometric. Lumidigm is developing such a fingerprint reader that allows you to move your hand in front of the sensor while it automatically captures the fingerprint image and verifies your identity. This sensor would be as easy to use as a barcode reader with the security of a fingerprint reader.
The Lumidigm development system for non-contact fingerprinting uses a new poly-imaging system. The system is based on a combination of photometric stereo and stereo imaging technologies. A hardware development system has been built by customizing and combining two imaging sensors currently used in the Lumidigm Venus fingerprint sensors. The development system is comprised of two synchronized color CMOS imagers that are aligned to view the same region of space located approximately 10 cm above the front surface of each imager’s lens. This region of space is simultaneously illuminated by three LEDs of different colors (red, green, and blue) from three different angles. When a finger is placed in the field of view, both imagers collect images of the finger from two different view points and illuminated from three distinct angles.
Non-contact collection GUI
The interface provides an ability to acquire the synchronized video streams at approximately 10 FPS. The streams go through a circular buffer so that when an acquisition is triggered, the current frame as well as 29 prior frames from both video streams are available for subsequent processing. This capability was incorporated to facilitate a temporal analysis of the data as well as the static analysis.
A graphical user interface for image collection is also a part of the development system. The GUI shows the two separate images as well as a focus metric. The focus metric gives the user visual cues to aid the user in good placement of the finger to capture properly focused images. This metric is based on the vertical and horizontal Sobel gradients that are calculated for both images.
Image capture is initialized by the user. Once initialized, the system detects the presence of a finger in the imaging area and triggers the capture sequence. A series of images is acquired for which a focus profile is computed. At the end of the process the system retains the image pair with the highest focus number for further processing. The focused images can be saved for off-line analysis.
Fingerprint image with minutiae points overlayed
The key aspect of the stereo imaging system is to combine the raw image data into a single quasi-3D representation from which biometric data can be extracted. The algorithmic approach is based on concepts from stereo imaging and shape from color.
Concept non-contact system
Initial biometric performance studies using a small data set of finger images has been conducted by Lumidigm. The matching between the samples lead to a good separation between genuine and impostor scores suggesting strong biometric capabilities of the prototype. Further development will lead to hardware in a very small form factor useful in a wide range of applications.
Genuine and impostor match scores
