METHOD AND APPARATUS FOR REDUCTION OF TRAPEZOIDAL DISTORTION AND IMPROVEMENT OF IMAGE SHARPNESS IN AN OPTICAL IMAGE CAPTURING SYSTEM

摘要

An apparatus and method for acquiring an image of a patterned object such as afingerprint including a light refractingdevice, a focusing lens, and a light source. The light refracting device can,for example, be a prism and includes an imaging surface,a light receiving surface and a viewing surface. Incident light from the lightsource is projected through the light receiving surfaceand reflected off a surface other than the imaging surface. This reflectedlight is then projected onto the imaging surface to createan image of the patterned object from substantially all scattered lightthrough the viewing surface. The lens is placed adjacent to theviewing surface to focus the light on an image sensor. The apparatus isconfigured to reduce or substantially eliminate trapezoidaldistortion and improve overall image sharpness in an image of an objectcreated by the apparatus.