There have been numerous optical technologies for palm-print identification in recent years. The uniformity of illumination and field of view limitations of these systems make it challenging to take high-quality photographs of palm prints at ultra-short distance range. We proposed a visible-lighting system with high illuminance, homogeneity, and lighting efficiency specifically for palm-print recognition applications as a solution to these problems. We enumerated the theoretical underpinnings and walk through the process of designing the ultra-short-range circular lighting system. The next step was to select a combination of surface textures and materials with an appropriate ratio of the diffusion agent to balance the illuminations at both the near-end and the far-end. A trade-off between illumination uniformity and system efficiency is revealed by the analysis of experimental data: near-end illumination favors high uniformity and so requires high scattering, whereas far-end illumination prefers high efficiency and thus requires low scattering. We achieved the trade-offs design goal by ensuring the illumination at the far end with an acceptable diameter and enhancing the illumination at the center of the near end by developing a distinctive inwardly curved surface. Our ultra-short-distance (30 mm) lighting solution obtained over 80% illumination uniformity in the recognition area and an 80% increase in the far-end efficiency of the illumination system. We believe the theoretical basis and data compiled in this paper are beneficial to the development of the palm recognition industry and also applicable to other related near-field image acquisition systems.
KEYWORDS: Light sources and illumination, Light emitting diodes, LED lighting, Veins, Infrared imaging, Cameras, Infrared radiation, Design and modelling, Power consumption, Refractive index
The existing palm vein recognition equipment cannot fully illuminate the palm at the near end (30 mm), and the illumination is low at the far end (120 mm), it is challenging for the poor palm vein images to meet the financial grade biometric accuracy requirements. This is due to the specification limitation of the lighting system components. We propose a compact rectangular-FOI infrared lighting system for palm-print and palm vein recognition with high uniformity and high efficiency. This ultra-short-distance (30 mm) lighting solution achieved a 200% increase in system efficiency, with illuminance uniformity of over 60% at the near end and over 90% at the far end. We have developed a novel LED component and a light distribution lampshade with multiple refractive index resins, according to the inverse square law of light, reduce the center illuminance and enhance the illuminance of the edge area at the target projection plane. It supports a broader working distance range for palm recognition, offers a more simplified design, and provides a more natural user experience. The proposed system is endowed with three significant advantages. Firstly, it matches the lighting FOI with the camera FOV to increase efficiency. Secondly, it provides high illuminance uniformity with fewer lighting components, eliminating the need for complex lighting layouts. Thirdly, it avoids the utilization of diffuse materials for enhancing uniformity, which would otherwise result in reduced light transmittance. The simplified lighting source layout, which requires only two or even one component, significantly reduces system design difficulty.
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