# Evaluation of a Vein Biometric Recognition System on an Ordinary Smartphone
## 3 Creation of a Database with a Viewer App for Vein Images  
In this work, a Xiaomi Redmi Note 8 smartphone and the IRVeinViewer app were used for the acquisition of the images. The used smartphone has an ordinary quad camera with 48 mega pixels. As many other smartphone cameras, it has a NIR blocking filter to improve the quality of the acquired images. Hence, acquisition of veins based on the absorption of the IR light is not possible. The IRVeinViewer App is a free Android application that can be used as a vein scanner. Currently, there are other similar apps, such as VeinSeek, VeinCamera, or VeinScanner. These apps transform the images captured in the visible spectrum into NIR-like images by enhancing the contrast and visualization of green and blue channels. The limitation is that only the most superficial veins can be detected. The common use of these apps is for medical applications, not for biometric recognition purposes. Once the IRVeinViewer app is started, the user has to focus the body area with the back camera. The application adjusts the optimal contrast and shows the simulated IR images in real-time on the smartphone screen. Figure 1 shows acquisition examples. Since we noticed that deep veins (like palm and finger veins) were not well acquired with the app, we focused on veins from the dorsal hand and wrist. Some factors must be considered besides the acquisition device: biological, environmental, and sample position. Regarding biological factors, the thickness of the subcutaneous layers can hinder the acquisition of veins correctly, and diseases (such as anemia, hyperthermia, or hypotension) can influence the way in which blood flows through the veins. Regarding environmental factors, sunlight contains a part of the infrared wavelength spectrum that converts images from blue to violet, and the recogn  
Figure 1: Examples of acquisition with the IRVeinViewer app: (**a**,**c**) acquisition procedure; (**b**,**d**) final images obtained. affected in this situation. Changes in temperature and humidity can also affect how blood flows through the veins. In order to evaluate environmental factors, different day times under five conditions were considered:  
* Outdoor: open areas with non-direct sunlight. * Indoor natural light 1: closed areas (inside a building) with natural light. * Indoor natural light 2: closed areas with natural light and a dark homogeneous background to capture the sample. * Indoor artificial light: closed areas (inside a building) with artificial light. * Indoor darkness: closed areas in absence of light. It is important to consider that the smartphone flashlight was always used, since it was not possible to turn it off. This could affect the acquisition in certain light conditions. Veins from the wrist and dorsal hand (2 body areas) were acquired from 10 volunteers for both left and right hands (2 sides). For each condition, 5 samples were taken. The complete database is composed of 1000 veins images (10 individuals \(\times\) 2 body areas \(\times\) 2 sides \(\times\) 5 conditions \(\times\) 5 samples). The ages of the volunteers ranged from 18 to 75 to assess biological factors. The average age in the participants of this database is 36.4 years. Additionally, both genders were considered, with 8 women and 2 men. The acquisition followed a protocol with the following steps:  
* Inform about the target and procedure of the acquisition. * Deliver an informed consent document. * Collect information about age and gender. * Capture 5 biometric samples considering body side and area (left wrist, left dorsal hand, right wrist, and right dorsal hand) and condition (outdoor, indoor natural light 1, indoor natural light 2, indoor artificial light, and darkness). Samples were acquired by the individuals who held the smartphone and interacted with the app. Since the IRveinViewer has not been developed to take pictures, the samples were collected by means of screenshots. In general, individuals tried to acquire samples containing enough information about the veins.