Importance

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Abstract

An apparatus for imaging a fingerprint or a topographic relief pattern (i.e., ridges) on the surface of an object comprising: (a) a transparent platen having a top layer of microprisms in a matrix form and a bottom layer of a platen substrate, the top of the layer of microprisms being the surface against which the object is pressed and the bottom surface of the platen substrate being provided for receiving light to illuminate the object surface, both layers of materials having equal or nearly equal refractive indices; (b) a light source with a focusing lens for providing substantially uniform and parallel light rays; (c) a beam splitter for splitting incident light emitted by the light source into tow parts, one part passing through and the other part being reflected by 90 degrees, the beam splitter being positioned at an angle to the object contact surface of the platen so that the reflected beams of the split light enter the platen bottom surface perpendicularly; (d) a 2-D photo electric image sensor with an imaging lens for receiving light reflected from portions of the platen surface not in contact with the object ridges so as to produce an object surface image, the image sensor having a focal plane which is positioned in such a manner such that the focal plane is parallel to portions of the platen surface in contact with the object. The microprisms has sufficient elasticity so that they become deformed when pressed by the object, and return to their original shape when the object impression is released. A fraction of light emitted by the light source enters the platen substrate perpendicularly by means of the beam splitter and travels forward toward faces of the microprisms, the light rays reverse their traveling directions if the microprism faces impinged by the light rays are not in contact with the object ridges and the reversed light rays are then received by the image sensor to give rise of bright regions on the dark background in the object surface image, the dark background is associated with the microprism surfaces which are in contact with the object ridges and is due to sweat on the object ridges or the deformation of the microprism faces.

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First Claim