Corrective optical component

• US 6,373,969 B1
• Filed: 03/15/1999
• Issued: 04/16/2002
• Est. Priority Date: 03/15/1999
• Status: Expired due to Fees

• Current Assignee: Activcard Ireland, Limited
• Original Assignee: Activcard Ireland, Limited
• Inventors: Adler, Andrew
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): AZARIAN, SEYED H
• Application Number:
  US09/267,615
• Time in Patent Office: 1,128 Days
• Field of Search: 382/114, 382/115, 382/116, 382/124, 382/126, 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

An optical imaging device such as a fingerprint imager is disclosed that has an optical modification to reduce perspective distortion in a read image. The optical modification is a contoured lens, a contoured platen recess, a contoured output port, or a contoured reflective surface that compensates for perspective distortion. The optical modification is provided by a complex optical surface and is distinct for a uniformly planar, spherical or cylindrical lens. In addition, a method for determining a perspective distortion correction is disclosed.

Claims

1. A corrective optical component comprising:

an input port for input light;

an output port comprising a smooth contoured complex surface for altering a path of light emerging from the output port, the smooth contoured complex surface shaped for correcting a perspective distortion; and

,

a platen for receipt of a biometric surface and for reflecting some of the input light received at the input port toward the output port.

2. A perspective correction optical component according to claim 1, wherein the smooth contoured complex surface defines a recess.

3. An optical component as defined in claim 2 wherein the smooth contoured complex surface has a concave contour.

4. A perspective correction optical component according to claim 3, wherein the recess describes a surface contour other than a planar, cylindrical or spherical surface contour.

5. An optical component as defined in claim 3 wherein the smooth contoured complex surface has a contour for altering the path of light emerging from the output port, the path altered to narrow a beam of light along an axis perpendicular to an axis of the perspective distortion.

6. An optical component as defined in claim 1 wherein the smooth contoured complex surface has a convex contour.

7. An optical component as defined in claim 6 wherein the smooth contoured complex surface has a contour for altering the path of light emerging from the output port, the path altered to magnify a beam of light along an axis of the perspective distortion.

8. A corrective optical component comprising:

an input port;

an interrogating light source for launching light into the input port;

a platen having a platen surface for receipt of a biometric surface, the platen surface for reflecting light received from the input port;

a perspective correction optical component including a contoured surface shaped for altering the path of the reflected light to correct for a perspective distortion of the biometric surface; and

,

a detector for receiving the corrected reflected light and for providing a signal in dependence thereon.

9. A corrective optical component according to claim 8, wherein the perspective correction optical component comprises a contoured platen, wherein the contours of the platen are complex.

10. A corrective optical component according to claim 8, wherein the input port, the platen and the perspective correction optical component are in the form of a single optical element and wherein the perspective correction optical component comprises a contoured surface disposed optically between the platen and the detector, wherein the contours of the surface are complex.

11. A corrective optical component according to claim 8, wherein the perspective correction optical component comprises a contoured lens, wherein the contours of the lens are complex.

12. A corrective optical component according to claim 8, wherein the perspective correction optical component comprises a contoured reflective surface, wherein the contours of the reflective surface are complex.

13. A method of determining a perspective distortion correction for an optical contact imager having a platen and an image sensor for detecting light received from the platen, the method comprising the steps of:

(a) selecting a platen scan line on the platen;

(b) selecting an image scan line on the image sensor;

(c) selecting pairs of points each pair comprising a point on the platen scan line and a corresponding point on the image scan line;

(d) determining a two-dimensional surface contour function for constructing a smooth contoured complex surface shaped for correcting the perspective distortion by directing light from each point within the platen scan line to a corresponding point within the image scan line.

14. A method of determining a perspective distortion correction for an optical contact imager as defined in claim 13 comprising the step of:

iterating steps (a) to (d) for a plurality of platen scan lines and corresponding image scan lines.

15. A method of determining a perspective distortion correction for an optical contact imager as defined in claim 14 wherein during each iteration a scan line adjacent that scan line selected for a previous iteration is selected and wherein the determined surface contour has a similar function with parameters thereof varied within predetermined limits to produce a smooth optically corrective contour function.

16. A method of determining a perspective distortion correction for an optical biometric-imager according to claim 15, wherein adjacent scan lines are parallel to each other.

17. A method of determining a perspective distortion correction for an optical biometric-imager according to claim 14, wherein the step of determining a two-dimensional surface contour function comprises the steps of:

determining a function describing the determined contour;

determining at least a modifiable parameter within the function;

during iterations after the first iteration, varying the at least a parameter of the function within predetermined limits to determine a further two-dimensional surface contour defined by the same function having varied parameters which describes a further optically corrective surface contour.

18. A method of determining a perspective distortion correction for an optical biometric-imager according to claim 17, such that the two-dimensional surface contour function and the further two-dimensional surface contour function vary smoothly from one to the other.

19. A method of determining a perspective distortion correction for an optical biometric-imager according to claim 17, wherein the determined surface contour is hyperbolic.