Biometrics holds a range of techniques for identity verification using physical data and/or behavioral such as handwriting recognition, Iris recognition, speech recognition and fingerprint recognition.
In the past, the acquirement of fingerprint images was performed by “ink-technique” which is also referred as off- line fingerprint acquisition in the law enforcement. Now-a-days, fingerprint sensors are used. Most of the sensors available today use “touch” method since it is simple and little training is required. These touch sensors acquire fingerprint images as the user’s fingerprint is contacted on a solid flat sensor. Both the sensor method and ink-technique requires the person to press his/her finger against a flat rigid surface. For this reason they are known as touch-based methods. But there are some basic problems of touch-based fingerprint. These are:
- Distortions by skin deformation
- Image quality degradation by skin condition changes & Latent problem
- Minuate information changes
- Fake fingerprints
- Worn fingerprint and scratch : aging
- Hygiene and contamination : germs, inflections
To overcome the above limitations, touch-less fingerprint technology came into existence. This technology is known as touch-less fingerprint technology .The touch-less fingerprint technology requires no contact between the skin of the finger and the sensing area. Touch-less fingerprint technology is a remote sensing technology to capture the ridge-valley pattern which provides essential information for recognition. Because of the lack of contact between the finger and any rigid surface, the skin does not deform during the capture and the repeatability of the measure is quite ensured.
Digital camera is used to present a touch-less fingerprint recognition system. Fingerprint images that are acquired using digital camera consist of certain constraints such as low contrast between the ridges and the valleys, defocus and motion blurriness.
Touch-less fingerprint recognition system comprises of three stages:-
- Preprocessing: Preprocessing is an essential step in detecting minutiae from the fingerprints. It is used to reduce the noises and increase the contrast between ridges and valleys.
- Feature extraction: The feature vectors are extracted from the images after preprocessing. The Gabor filter based feature extractor is used to form the feature vectors.
- Matching: For the comparison purpose in verifying the individuality of a person through the feature matching, many distance measures can be adopted like Manhattan distance, Euclidean distance and Cosine .The result of the experiments justify that Cosine Angle is the best measure.
There are different approaches to capture a fingerprint based on touch-less technology. The approaches can be grouped in two families:
Reflection-based Touch-less Finger Imaging
In RTFI, the light sources are placed in front of the fingerprint to illuminate it. Part of this light is absorbed by the skin, while the majority is reflected and thus, collected by a detector. The quantity of light energy incident on the detector surface is quantized to 256 gray values, providing the final image representing a fingerprint.
Transmission-based Touch-less Finger Imaging
This touch-less capture approach, is based on the transmission of the light through the finger. This time, the light sources are placed in such a way that they illuminate the nail side. Red light with a wavelength of 660 nm is used, because it has high transmittance ratio to the skin tissue. Hence, the light penetrating the finger is collected by the detector placed in front of the fingerprint.
Some of the advantages of touch-less fingerprint technology are:
No discrimination: No sex, race, age related enrollment issues
No Latent Fingerprints:. It is therefore impossible for the sensor to make errors due to latent fingerprints.
No restriction on number of users: there are any restrictions on the number of users as the technology is touch-less.
Identification accuracy: The ridges on the fingers are always reproduced in consistently high quality, independent of the finger’s appearance, pressure applied or ambient conditions. There are no problems of false minutiae or bad contact.
Large Clear Image: The touch-less technology allows for clear, precise pictures that are not influenced by movements on a contact surface.
Robust and Reliable: Dirt or dust on the protective glass has virtually no influence on the quality of the image and the function of the sensor.
Maintenance free and durable: The complete sensor optic is protected behind a glass screen and never is touched when in use.
User comfort: The assembly is extremely easy to use. Touch-free fingerprint identification allows the highest standard of hygiene, which further increases the system’s user acceptance
Touch-less fingerprint recognition is considered as a feasible alternative to touch-based fingerprint recognition technology. Touch-less fingerprint technology provides a near perfect solution to the problems in terms of hygienic, maintenance and latent fingerprints.
Written by Pooja Gautam