These systems also avoid the time consuming and messy process of obtaining fingerprints by using ink and rolling the inked fingers across a printing surface.
Such systems provide a means of creating fingerprint images for purposes of storage, analysis, or printing. Optical systems have been developed for imaging fingerprints directly from the contact of a person's finger with a platen or prism. The present invention relates generally to apparatus for recording fingerprint images, and more particularly, to an apparatus which eliminates image artifacts which have been found to be attributable to moisture on the finger being imaged. The apparatus of 1, wherein light from the light source illuminating the platen is incident on the platen at an angle with respect to a normal to the platen surface which is approximately equal to zero degrees. The apparatus of 1, wherein light from the light source illuminating the platen is incident on the platen at an angle with respect to a normal to the platen surface which is greater than the critical angle corresponding to an interface of the optical platen and water, and less than the critical angle corresponding to an interface of the optical platen and the finger being imaged.ĥ. The apparatus of claim 1 wherein the optical platen is glass having an index of refraction of 1.62 to 1.65 and the angle θ is 57 to 60 degrees.Ĥ. The apparatus of claim 1 wherein an index of refraction of the optical platen is greater than 1.52.ģ.
#ANGLE OF INCIDENT EQUALING AN ANGLE OF REFLECTION FREE#
Mounting means for positioning the optical platen and light detector means in their respective relative positions, whereby an image of a print of a finger positioned on the platen surface may be obtained substantially free of artifacts resulting from the presence of moisture on the finger.Ģ. Light detector means for detecting light originating from the light source which is reflected from the finger-receiving surface of the platen, wherein the platen and light detector means are positioned relative to one another so that the light detector means detects light having an axis of propagation which is at an angle, θ, relative to the platen surface normal, where the angle θ is greater than the critical angle corresponding to an interface of the optical platen and water, and less than the critical angle corresponding to an interface of the optical platen and the finger being imaged, and An apparatus for imaging a finger, comprising:Īn optical platen having a finger-receiving surface:Ī light source for illuminating the platen
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