Radiation optimization and image processing algorithms in the identification of hand vein patterns Septimiu Crisan ⁎, Ioan Gavril Tarnovan, Titus Eduard Crisan Department of Electrical Measurement, Faculty of Electrical Engineering, Technical University of Cluj-Napoca, Str.C.Daicoviciu nr.15, 400020 Cluj-Napoca, Romania abstract article info Available online 13 November 2009 Keywords: Biometric recognition Infrared scanning Vein patterns Image processing Vein pattern recognition is one of the newest biometric techniques researched today. While the concept behind the method is simple, there are various challenges to be found throughout the design and implementation of a vein-scanning device concerning the lighting system and the image processing algorithms. To achieve low scanning errors, the acquired image should be almost noiseless and the algorithms should detect the vein pattern in various conditions. Many implementations of this method are now in a commercial phase and there is a great need for low cost systems that can detect human veins with minimum computational requirements. © 2009 Elsevier B.V. All rights reserved. 1. Introduction A biometric system is essentially a pattern-recognition system that recognizes a person based on a feature vector derived from specific physiological or behavioral characteristic that the person possesses [1]. A vein pattern detection has been proved to fully comply with this definition [2,3] and it provides many important biometric features: • uniqueness and permanence of the pattern • noncontact detection procedure • almost impossible to forge or copy • the biometric parameter is hidden from general view • the vein pattern is intricate enough to allow sufficient criteria for positively detecting various subjects, even identical twins. The vein detection process consists of an easy to implement device that takes a snapshot of the subject's veins under a source of infrared radiation at a specific wavelength. The system is able to detect veins but not arteries due to the specific absorption of infrared radiation in blood vessels. Almost any part of the body could be analyzed in order to extract an image of the vascular pattern but the hand and the fingers are preferred. The reason for this choice is the general availability of the hand. A sketch of an actual vein detection system is shown in Fig. 1. The infrared radiation is absorbed in a different way in various types of tissue. In order to achieve visual penetration through the respective tissue, lighting should be performed under a very tight optical window namely 740 nm up to 960 nm (inside the near infrared part of the electromagnetic radiation spectrum). Because of the optical properties of the human tissue, a near IR vein-scanning device cannot penetrate very deep under the skin therefore the device will recognize the superficial veins and rarely the deep veins. Good candidates for the scanning procedure are the dorsal metacarpal veins and the general dorsal venous network. A statistical maximum penetration distance is 3 mm and this poses some limitations on the quantity and quality of the extracted vein pattern. Two basic optical coefficients are involved in this absorption process: - absorption coefficient ∝a - scattering coefficient ∝s. The absorption coefficient ∝a determines how far light can travel before losing its intensity while still in its original path, and, the scattering coefficient ∝s determines how far light can travel before losing its original phase and changes direction [13]. Taking these optical properties into account it is obvious that the lighting source should be uniform throughout the region of interest, the degree of illumination should be kept constant for different acquisitions and the contrast of the resulting image should be sharp enough to reduce the need for complex post processing image algorithms. 2. Hardware setup and radiation source design As mentioned in the introduction, the hardware setup has a crucial role in the acquisition of vein images. Two aspects can be underlined here: o the actual camera used for taking the snapshot has only one important parameter, the response to near infrared radiation. Computer Standards & Interfaces 32 (2010) 130–140 ⁎ Corresponding author. E-mail address: crisans@mas.utcluj.ro (S. Crisan). 0920-5489/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.csi.2009.11.008 Contents lists available at ScienceDirect Computer Standards & Interfaces journal homepage: www.elsevier.com/locate/csi