EP0308162A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Optical system for fingerprint imaging
Assignee: Idemia Identity and Security USA LLC
•
Filing: 1988-09-12
•
Granted: —
•
Expires: 2008-09-12
Abstract
Abstract An optical system for fingerprint imaging utilizing a platen prism (14) and a correction prism (30). The platen prism includes a platen area (18) on one face for receiving a finger to be imaged. Light from a monochromatic light source (22) enters the platen prism through a second face (18) and is totally internally reflected at the platen area surface except in the regions where ridges of the finger directly contact the platen prism. The correction prism (30) receives the light from the platen prism. An objective lens (38) receives the light from the correction prism and forms a fingerprint image on a light detector. The geometry and placement of the correction prism, with respect to the platen prism, are selected to reduce defocussing of the fingerprint image on the detector introduced by the tilting of the platen area with respect to the axis of the objective lens. The light detector (48), typically an area array detector such as a charge coupled device array, provides an output used for fingerprint verification and the like. Preferably, the correction prism, in combination with the platen prism, also provides anamorphic magnification of the fingerprint image thereby permitting the aspect ratio of the image to be controlled. Thus, the image aspect ratio can be selected to match the aspect ratio of the light sensitive cells which form the area array detector.
Inventors
- 👤 Thomas F. Sartor
- 👤 Edward C. Driscoll, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 20:46
CPC Classifications
A; A61; A61B; A61B5/00; A61B5/117; A61B5/1171; A61B5/1172; G; G06; G06V; G06V40/00; G06V40/10; G06V40/12; G06V40/13; G06V40/1324
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
323 words
An optical system for fingerprint imaging comprising: light means for producing a source of light; a platen prism having first, second and third faces, with said second face having a rectangular-shaped platen area for receiving a finger to be imaged, with said area having first and second opposite edges generally parallel to the line of intersection of the planes defined by said second and third faces, and with said light means and said platen prism being positioned relative to one another such that light from said light means enters said platen prism through said first face, strikes said second face at an angle of incidence greater than a critical angle determined by the respective indices of refraction of said prism and a medium adjacent said second face so that light is internally reflected at said second face which exits said platen prism through said third face, with light reflected from said platen area on said second face forming a fingerprint image when a finger is positioned on said platen area; an objective lens having an optical axis, an optical plane at an entrance of said objective lens normal to said optical axis and an entrance pupil; light detector means for detecting light provided by said objective lens; a correction prism, intermediate said platen prism and said objective lens, having fourth and fifth faces which define a correction prism angle therebetween, with said correction prism angle and the relative positions of said correction prism and said platen prism being selected such that light from said third face of said platen prism enters said correction prism through said fourth face and exits from said fifth face and is received by said objective lens and further selected so that a difference in effective optical path lengths of principal rays of light reflected at said first edge of said platen area and said second edge of said platen area to said objective lens optical plane is reduced.
Claim 2
Dependent Claim
323 words
An optical system for fingerprint imaging comprising: light means for producing a source of light; a platen prism having first, second and third faces, with said second face having a rectangular-shaped platen area for receiving a finger to be imaged, with said area having first and second opposite edges generally parallel to the line of intersection of the planes defined by said second and third faces, and with said light means and said platen prism being positioned relative to one another such that light from said light means enters said platen prism through said first face, strikes said second face at an angle of incidence greater than a critical angle determined by the respective indices of refraction of said prism and a medium adjacent said second face so that light is internally reflected at said second face which exits said platen prism through said third face, with light reflected from said platen area on said second face forming a fingerprint image when a finger is positioned on said platen area; an objective lens having an optical axis, an optical plane at an entrance of said objective lens normal to said optical axis and an entrance pupil; light detector means for detecting light provided by said objective lens; a correction prism, intermediate said platen prism and said objective lens, having fourth and fifth faces which define a correction prism angle therebetween, with said correction prism angle and the relative positions of said correction prism and said platen prism being selected such that light from said third face of said platen prism enters said correction prism through said fourth face and exits from said fifth face and is received by said objective lens and further selected so that a difference in effective optical path lengths of principal rays of light reflected at said first edge of said platen area and said second edge of said platen area to said objective lens optical plane is reduced.
Claim 3
Dependent Claim
25 words
The optical system of Claim 1 wherein said difference in effective optical path lengths is reduced to less than 5% of the average path length.
Claim 4
Dependent Claim
49 words
The optical system of Claim 2 wherein said correction prism angle and said relative positions of said correction prism and said platen prism are also selected to produce anamorphic magnification of said fingerprint image along a first axis normal to said first and second edges of said platen area.
Claim 5
Dependent Claim
66 words
The optical system of Claim 3 wherein said light detector means includes an area array detector comprised of light sensitive cells, with said cells arranged with respect to one another so as to have a predetermined cell aspect ratio and wherein said anamorphic magnification is selected such that said fingerprint image has an image aspect ratio at said optical plane which matches said call aspect ratio.
Claim 6
Dependent Claim
15 words
The optical system of Claim 4 wherein said cell aspect ratio is other than unity.
Claim 7
Dependent Claim
17 words
The otpical system of Claim 4 wherein said area array detector is a charge coupled device array.
Claim 8
Dependent Claim
20 words
The optical system of Claim 4 further including an aperture stop intermediate said objective lens and said area array detector.
Claim 9
Dependent Claim
35 words
The optical system of Claim 4 wherein said aperture stop includes an asymmetrical aperture with the height of said aperture along said first axis of anamorphic magnification being less than the width of said aperture.
Claim 10
Dependent Claim
18 words
The optical system of Claim 2 wherein said light produced by said light means is substantially monochromatic light.
Claim 11
Dependent Claim
15 words
The optical system of Claim 9 wherein said light means includes a light emitting diode.
Claim 12
Dependent Claim
23 words
The otpical system of Claim 10 wherein said light means inlcudes a condenser lens intermediate said light emitting diode and said platen prism.
Claim 13
Dependent Claim
24 words
The optical system of Claim 11 wherein said light means includes an optical diffuser disposed between said light emitting diode and said condenser lens.
Claim 14
Dependent Claim
23 words
The optical system of Claim 12 wherein said condenser lens is a fresnel lens and light existing said fresnel lens is collimated light.
Claim 15
Dependent Claim
19 words
The optical system of Claim 13 wherein said fresnel lens, said platen prism and said correction prism are plastic.
Claim 16
Dependent Claim
17 words
The optical system of Claim 2 wherein said objective lens entrance pupil is a remote entrance pupil.
Claim 17
Dependent Claim
61 words
The optical system of Claim 15 wherein the distance between said remote entrance pupil and the said fifth face is sufficient to reduce an angle between said principal rays from said first and second edges with respect to an axial principal ray from a point on said platen area equidistant from said first and second edges to less than 10 degrees.
Claim 18
Dependent Claim
127 words
An optical system for fingerprint imaging comprising: light means for producing a source of light; a platen prism having one face that includes a platen area for receiving a finger to be imaged, with said light means and said platen prism being positioned relative to one another so that light enters said platen prism and is internally reflected at said platen area on said one face so as to produce a fingerprint image when a finger is positioned on said platen area; a correction prism positioned for receiving said fingerprint image directly from said platen prism; an area array light detector; and an objective lens positioned so as to receive light from said correction prism and to form said fingerprint image on said area array light detector..
Claim 19
Dependent Claim
127 words
An optical system for fingerprint imaging comprising: light means for producing a source of light; a platen prism having one face that includes a platen area for receiving a finger to be imaged, with said light means and said platen prism being positioned relative to one another so that light enters said platen prism and is internally reflected at said platen area on said one face so as to produce a fingerprint image when a finger is positioned on said platen area; a correction prism positioned for receiving said fingerprint image directly from said platen prism; an area array light detector; and an objective lens positioned so as to receive light from said correction prism and to form said fingerprint image on said area array light detector..
Claim 20
Dependent Claim
20 words
The optical system of Claim 17 wherein said light means includes a light emitting diode which provides substantially monochromatic light.
Claim 21
Dependent Claim
27 words
The optical system of Claim 18 wherein said light means includes a fresnel lens and a light diffuser intermediate said fresnel lens and said light emitting diode.
Claim 22
Dependent Claim
19 words
The optical system of Claim 19 wherein said fresnel lens, said platen prism and said correction prism are plastic.
Claim 23
Dependent Claim
55 words
The optical system of Claim 17 wherein said correction prism includes a pair of faces which form a correction prism angle, wherein said correction prism angle and the relative positions of said platen prism and said correction prism are selected such that defocussing of said fingerprint image formed on said area array detector is reduced.
Claim 24
Dependent Claim
71 words
The optical system of Claim 21 wherein said area array detector includes an array of light sensitive cells arranged with respect to one another to provide a predetermined cell aspect ratio and wherein said correction prism angle and said relative position of said platen prism and said correction prism are further selected such that said fingerprint image formed on said array has an aspect ratio which matches said cell aspect ratio.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
Maintenance schedule is calculated for granted US utility patents.