High contrast, low distortion optical acquistion system for image capturing

• US 6,381,347 B1
• Filed: 11/12/1998
• Issued: 04/30/2002
• Est. Priority Date: 11/12/1998
• Status: Expired due to Term

• Current Assignee: SecuGen Corporation (Pivotec Corp.)
• Original Assignee: SecuGen Corporation (Pivotec Corp.)
• Inventors: Teng, Harry H., Jo, Sung-Chan
• Primary Examiner(s): Boudreau, Leo
• Assistant Examiner(s): Werner, Brian P.
• Application Number:
  US09/191,428
• Time in Patent Office: 1,265 Days
• Field of Search: 382/124-127, 382/116, 382/312, 382/315, 382/321, 382/275, 382/108, 356/71, 340/5.53, 340/5.83, 902/3, 902/6, 713/186, 359/438, 359/638, 359/831, 359/837, 358/511
• US Class Current: 382/127
• CPC Class Codes: G06V 40/1324 by using geometrical optics, e.g. using prisms G06V40/1312 takes precedence

Abstract

An apparatus and method for acquiring an image of a patterned object such as a fingerprint including a light refracting device, 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 light source is projected through the light receiving surface and reflected off a surface other than the imaging surface. This reflected light is then projected onto the imaging surface to create an image of the patterned object from substantially all scattered light through the viewing surface. The lens is placed adjacent to the viewing surface to focus the light on an image sensor.

Claims

1. A compact apparatus for forming a high contrast, low distortion image of a patterned object including:

a light refractor for reflecting and refracting light, the light refractor including;

an imaging surface against which a patterned object to be imaged is to be placed;

at least one light entrance surface adjacent to the imaging surface and through which light enters the refractor; and

a viewing surface adjacent to the imaging surface and through which an image of the object to be imaged is projected and which is the same surface as the light entrance surface;

a further surface positioned between and different from the imaging surface and the light entrance surface;

at least one focusing lens adjacent to the viewing surface and for receiving and focusing an image of a patterned object projected through the viewing surface; and

at least one light source located adjacent to the light receiving surface and for emitting incident light which enters the light refractor to create an image of the patterned object at the viewing surface, the image focused by the at least one focusing lens, the light source positioned such that light emitted therefrom and entering the light refractor strikes at least the further surface at an angle greater than the critical angle of the further surface before striking the imaging surface at an angle less than the critical angle of the imaging surface such that the image of the patterned object from the imaging surface and projected through the viewing surface is generated by substantially all scattered light from the imaging surface.

2. The apparatus of claim 1 wherein the light refractor is a five faced triangular prism and the imaging surface includes a first rectangular face of the triangular prism different from both the viewing surface and the light entrance surface.

3. The apparatus of claim 2 wherein light reflected from the further surface strikes the imaging surface at an angle less than a critical angle of the imaging surface.

4. The apparatus of claim 3 wherein the triangular prism is an isosceles prism.

5. The apparatus of claim 4 wherein:

the triangular prism includes;

a first edge opposite the imaging surface and adjacent to the light entrance surface; and

a second edge adjacent to the imaging surface; and

the light source is a strip of light emitting diodes (LEDs) oriented towards and parallel with the light entrance surface and adjacent to the first edge such that the LED strip does not pass through a plane normal to the light entrance surface and intersecting with the second edge.

6. The apparatus of claim 5 wherein the viewing surface includes the light entrance surface.

7. The apparatus of claim 6 wherein a light shield is positioned along a linear path between the light source and the image sensor so as to block light directly emitted from the light source from reaching the image sensor.

8. The apparatus of claim 5 wherein the further surface includes a light diffusing face, such that the light reflecting off the further surface before surface before striking the imaging surface is diffused by the light diffusing face.

9. The apparatus of claim 8 wherein a portion of the light receiving surface is mirrored towards the interior of the triangular prism.

10. The apparatus of claim 9 wherein a portion of the light receiving surface includes a light absorbing surface.

11. The apparatus of claim 10 wherein a portion of the further surface adjacent to the first edge is mirrored towards the interior of the triangular prism.

12. The apparatus of claim 11 wherein:

a lens plane of the focusing lens is tilted with respect to a plane defined by the viewing surface so as to reduce a difference in image light path lengths between different portions of an object to be imaged; and

the base angles of the isosceles triangular prism are greater than 45 degrees, such that trapezoidal distortion of an image is reduced.

13. The apparatus of claim 12 wherein the angle between the base angles of the isosceles triangular prism are between 50 degrees and 65 degrees, inclusive.

14. The apparatus of claim 5 wherein a portion of the light receiving surface adjacent to the first edge and facing the light source is streaked to cause diffusion of light passing through the light receiving surface.

15. The apparatus of claim 5 wherein the viewing surface is between the light entrance surface and the imaging surface.

16. The apparatus of claim 15 wherein a portion of the viewing surface adjacent to the first edge is mirrored towards the interior of the triangular prism.

17. The apparatus of claim 16 wherein a light shield is positioned along a linear path between the light source and the image sensor so as to block light directly emitted from the light source from reaching the image sensor.

18. The apparatus of claim 17 wherein a portion of the light receiving surface adjacent to the first edge and facing the light source is streaked to cause diffusion of light passing through the light receiving surface.

19. The apparatus of claim 2 wherein:

the triangular prism includes a first triangular end face opposite a second triangular end face; and

the at least one light source extends along and is co-extensive with an edge formed between the first triangular end face and a rectangular face of the triangular prism.

20. The apparatus of claim 19 wherein the at least one lens adjacent to the viewing surface is at least as wide as the viewing surface.

21. The image acquisition apparatus of claim 1 housed in a computer input device.

22. The device of claim 21 wherein the computer input device includes a mouse and the image acquisition system is housed inside the mouse.

23. The device of claim 22 wherein the refractor includes a isosceles triangular prism.

24. A method of imaging a patterned object comprising:

providing a light refractor having an imaging surface, a light receiving surface, a viewing surface which is the same as the light receiving surface and a further surface different from and between the light receiving surface and the imaging surface;

placing the patterned object against the imaging surface of the light refractor;

projecting incident light from a light source through the light receiving surface of the light refractor;

reflecting the incident light off at least the further surface at an angle greater than the critical angle of the further surface before the incident light strikes the imaging surface at an angle less than the critical angle of the imaging surface and

scattering the incident light off the imaging surface and patterned object and through the viewing surface.

25. The method of claim 24 further including the steps of:

providing a lens adjacent to the viewing surface; and

projecting the scattered light from the viewing surface into the lens to form an image of the patterned object.

26. The method of claim 25 wherein providing a light refractor includes providing an isosceles triangular prism having base angles which measure greater than 45 degrees.

27. The method of claim 26 wherein reflecting the incident light off the further surface of the triangular prism includes scattering the incident light off the further surface of the triangular prism.

28. The method of claim 27 wherein the step of providing a lens includes tilting the lens plane of the lens with respect to a plane of the viewing surface to reduce trapezoidal distortion in the image of the patterned object.