Iris Recognition - Visible Wavelength (VW) Vs Near Infrared (NIR) Imaging

Visible Wavelength (VW) Vs Near Infrared (NIR) Imaging

Most iris recognition systems acquire images of the iris in the visible wavelength (400-700 nm) or near infrared range (700 - 900 nm) of the electromagnetic spectrum. Each wavelength distinguishes different features of the iris with NIR and VW obtaining Information from the iris by its texture and pigmentation, respectively. The majority of iris recognition systems operate within the longer NIR spectrum which can penetrate dark-coloured irides, the dominant phenotype of the human population, revealing texture not easily observed in the VW spectrum. The NIR spectrum also reduces iris pattern contamination by blocking ambient corneal reflections.

Although reducing reflections through NIR makes system recognitions robust, NIR imaging cannot distinguish the effects of melanin, the primary colouring component in irides. The melanin, also known as chromophore, mainly consists of two distinct heterogeneous macromolecules, called eumelanin (brown–black) and pheomelanin (yellow–reddish), whose absorbance at longer wavelengths in the NIR spectrum is negligible. At shorter wavelengths within the VW spectrum, however, these chromophores are excited and provide rich sources of information mainly coded as shape patterns in iris. Hosseini, et al. provide a comparison between these two imaging modalities and fused the results to boost the recognition rate. An alternative feature extraction method to encode VW iris images was also introduced, which is highly robust to reflectivity terms in iris. Such fusion results are seemed to be alternative approach for multi-modal biometric systems which intend to reach high accuracies of recognition in large databanks.