Method and apparatus for illuminating a fingerprint through side illumination of a platen

• US 6,188,781 B1
• Filed: 07/28/1998
• Issued: 02/13/2001
• Est. Priority Date: 07/28/1998
• Status: Expired due to Term

• Current Assignee: Digital Persona Inc (Assa Abloy AB)
• Original Assignee: Digital Persona Inc (Assa Abloy AB)
• Inventors: Brownlee, Kenneth
• Primary Examiner(s): MEHTA, BHAVESH M
• Application Number:
  US09/124,182
• Time in Patent Office: 931 Days
• Field of Search: 382/115-116, 382/124-127, 356/71
• US Class Current: 382/127
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

The present invention provides a method and apparatus for illuminating a fingerprint. A finger is placed on a transparent platen which has a microprism array on one surface. A light source directs light through a horizontal plane of the platen to illuminate the finger. Light directed through the platen is substantially parallel to an axis of the microprism array and is largely contained within the body of the platen. The skin in contact with the platen is illuminated by the light, and the light is imaged by an imaging device.

Claims

1. An apparatus for illuminating a fingerprint comprising:

a transparent platen having sensing surface, a bottom surface, and sides, one of the surfaces including a microprism array; and

a light source positioned to direct light through a horizontal plane of the platen substantially parallel to an axis of the microprism array, the fingerprint illuminated using multiple total-internal-reflection (TIR) bounces of light rays down the plane of the platen, between the microprism array and the other surface to reach points of skin contact.

2. The apparatus of claim 1 further comprising a reflective surface on the side of the platen opposite to the light source.

3. The apparatus of claim 1 further comprising a reflective surface positioned adjacent to the platen opposite to the light source.

4. The apparatus of claim 1 wherein the platen comprises a plastic platen.

5. The apparatus of claim 1 wherein the platen comprises a glass platen.

6. The apparatus of claim 1 wherein the light source comprises a light-emitting diode (LED).

7. The apparatus of claim 1 further comprising an imaging device positioned to capture an image of the fingerprint.

8. The apparatus of claim 7 further comprising a focusing device positioned to focus the image of the fingerprint onto the imaging device.

9. The apparatus of claim 8 wherein the focusing device comprises one of the following:

a lens, a curved mirror, and a SELFOC lens.

10. The apparatus of claim 1, wherein the microprism array is located on the bottom surface.

11. The apparatus of claim 1, wherein the microprism array is located on the sensing surface.

12. The apparatus of claim 7 wherein the imaging device comprises a charge-coupled device (CCD).

13. The apparatus of claim 7 wherein the imaging device comprises a complementary metal-oxide semiconductor (CMOS) sensor.

14. The apparatus of claim 7 wherein the imaging device comprises a contact image sensor (CIS).

15. A method for illuminating a fingerprint comprising:

receiving a finger on a transparent platen having sensing surface, a bottom surface, and sides, one of the sensing surfaces including a microprism array; and

illuminating the fingerprint with a light source positioned to direct light through a horizontal plane of the platen substantially parallel to an axis of the microprism, the fingerprint illuminated using multiple total-internal-reflection (TIR) bounces of light rays down the plane of the platen, between a first surface and the microprism array to reach points of skin contact.

16. The method of claim 15 further comprising capturing an image of the fingerprint through the platen with an imaging device.

17. The method of claim 16 further comprising focusing the image of the fingerprint onto the imaging device.

18. The method of claim 15, further wherein the platen comprises a sensing surface, a bottom surface, and two sides, the method further comprising:

reflecting the light off a reflective surface located on a side of the platen opposite the light source.

19. The method of claim 18, further wherein the reflective surface is a mirrored surface.

20. The method of claim 18, wherein the microprism is a part of the bottom surface.

21. The method of claim 18, wherein the microprism is a part of the sensing surface.