Fingerprint scanner auto-capture system and method

• US 7,657,067 B2
• Filed: 12/29/2005
• Issued: 02/02/2010
• Est. Priority Date: 08/18/2000
• Status: Expired due to Term

• Current Assignee: HID Global Corporation (Assa Abloy AB)
• Original Assignee: Cross Match Technologies Incorporated (Assa Abloy AB)
• Inventors: Smith, David C.
• Primary Examiner(s): Chawan; Sheela C
• Application Number:
  US11/320,472
• Publication Number:
  US 20060110016A1
• Time in Patent Office: 1,496 Days
• Field of Search: 382/124, 382/274, 352/125, 352/169, 352/274, 352/232, 352/130, 352/173, 358/1.15, 358/504, 358/461, 358/501, 358/474, 348/247, 348/229.1, 348/243, 359/17
• US Class Current: 382/124
• CPC Class Codes: G06V 10/993 Evaluation of the quality of the acquired pattern
• CPC Class Codes: G06V 40/13 Sensors therefor

Abstract

A system and method of capturing an acceptable fingerprint image is disclosed herein. The method includes a step of capturing an initial fingerprint image at a nominal image integration time. Once this initial fingerprint image is captured, a first intermediate fingerprint image at a first intermediate image integration time is captured. Next, an image darkness test is performed followed by an image definition test. If one or more of these tests indicates that the first intermediate fingerprint image is unacceptable, a subsequent intermediate fingerprint image at a subsequent intermediate image integration time is captured. This subsequent intermediate fingerprint image can be captured before the image definition test is performed. Additional intermediate fingerprint images can be captured until an image that has an acceptable darkness level as a well as an acceptable definition level is captured. Also disclosed is a fingerprint scanner that performs this method.

Claims

1. A method of capturing an acceptable fingerprint image comprising the steps of:

(a) capturing with a scanner an initial fingerprint image at a nominal image integration time;

(b) capturing with the scanner a first intermediate fingerprint image at a first intermediate image integration time;

(c) performing with a processor an image darkness test on the first intermediate fingerprint image to determine if the first intermediate fingerprint image results in an acceptable image darkness level;

(d) performing with the processor an image definition test on the first intermediate fingerprint image to determine if the first intermediate fingerprint image results in an acceptable image definition level; and

(e) determining with the processor that the first intermediate fingerprint image is acceptable if the image darkness test results in an acceptable image darkness level and if the image definition test results in an acceptable image definition level.

2. A method of capturing an acceptable biometric image comprising the steps of:

(a) automatically capturing with a scanner an initial biometric image at a nominal image integration time;

(b) automatically capturing with the scanner a first intermediate biometric image at a first intermediate image integration time;

(c) performing with a processor an image darkness test on the first intermediate biometric image to determine if the first intermediate biometric image results in an acceptable image darkness level;

(d) performing with the processor an image definition test on the first intermediate biometric image to determine if the first intermediate biometric image results in an acceptable image definition level; and

(e) determining with the processor that the first intermediate biometric image is acceptable if the image darkness test results in an acceptable image darkness level and if the image definition test results in an acceptable image definition level.

3. The method of claim 2, further comprising a step (f) of capturing with the scanner a subsequent intermediate biometric image at a subsequent intermediate image integration time prior to said step (d) when said step (c) results in an unacceptable image darkness level.

4. The method of claim 3, further comprising repeating said step (f) at additional subsequent intermediate image integration times until said step (c) results in an acceptable image darkness level.

5. The method of claim 4, further comprising using a range of intermediate integration times that includes the nominal image integration time.

6. The method of claim 5, further comprising using multiples of 1/7 of the nominal image integration time as the intermediate image integration times.

7. The method of claim 3, further comprising repeating steps (b), (c), (d), (e), and (f) until said step (d) results in an acceptable image definition level.

8. The method of claim 2, wherein step (c) further comprises calculating with the processor average darkness values for a plurality of image darkness lines arranged in pairs of image darkness lines, said pairs of image darkness lines situated within an expected image capture region.

9. The method of claim 8, wherein the plurality of image darkness test lines includes a first pair of image darkness test lines, the first pair including a first image darkness test line and a second image darkness line, wherein the first image darkness test line intersects with the second image darkness test line, and wherein step (c) comprises calculating with the processor average darkness values for the first image darkness test line and the second image darkness test line.

10. The method of claim 2, wherein step (c) further comprises the steps of:

(c1) calculating with the processor average darkness values for a plurality of image darkness test lines;

(c2) verifying with the processor that overall image darkness is acceptable; and

(c3) verifying with the processor that image darkness distribution is acceptable.

11. The method of claim 10, wherein step (c2) further comprises verifying with the processor that a predetermined number of said plurality of image darkness test lines have associated calculated average darkness values that exceed a darkness threshold value.

12. The method of claim 2, further comprising the step of:

(f) performing said step (c) after a first companding curve is applied to the first intermediate biometric image.

13. The method of claim 12, further comprising the steps of:

(g) performing the following steps when said step (c) results in an unacceptable image darkness level;

(g1) repeating said step (a) and said step (b);

(g2) applying with the processor a subsequent companding curve to the subsequent biometric image captured in step (g1); and

(g3) repeating said step (c).

14. The method of claim 13, further comprising the step of repeating said step (g) until said step (c) results in an acceptable image darkness level.

15. A biometric scanner for capturing an acceptable image, comprising:

a camera configured to automatically capture an initial biometric image at a nominal image integration time and a first intermediate biometric image at a first intermediate image integration time; and

a processor configured to;

perform an image darkness test on the first intermediate biometric image to determine if the first intermediate biometric image results in an acceptable image darkness level;

perform an image definition test on the first intermediate biometric image to determine if the first intermediate biometric image results in an acceptable image definition level; and

determine that the first intermediate biometric image is acceptable if the image darkness test results in an acceptable image darkness level and if the image definition test results in an acceptable image definition level.

16. The biometric scanner of claim 15, wherein the camera is further configured to capture a subsequent intermediate biometric image at a subsequent intermediate image integration time when the processor performs an image darkness test that results in an unacceptable darkness level.

17. The biometric scanner of claim 16, wherein the camera is further configured to capture additional subsequent intermediate biometric images at subsequent intermediate image integration times until the processor performs an image darkness test that results in an acceptable darkness level.

18. The biometric scanner of claim 17, wherein the camera captures subsequent intermediate biometric images at subsequent intermediate integration times until both the image darkness test and the image definition test result in acceptable darkness and definition levels respectively for a single biometric image.

19. The biometric scanner of claim 18, wherein the camera is further configured to determine the intermediate image integration times from the nominal image integration time.

20. The biometric scanner of claim 19, wherein the camera is further configured to determine the intermediate image integration times using multiples of 1/7 of the nominal image integration time.

21. The biometric scanner of claim 15, wherein the processor is further configured to calculate average darkness values for a plurality of image darkness test lines arranged in pairs of image darkness lines, said pairs of image darkness lines situated within an expected image capture region.

22. The biometric scanner of claim 21, wherein the processor is further configured to determine if a predetermined number of said plurality of image darkness test lines have associated calculated average darkness values that exceed a darkness threshold value.

23. The biometric scanner of claim 15, wherein the processor is further configured to determine if (1) overall image darkness is acceptable and (2) image darkness distribution is acceptable.

24. The biometric scanner of claim 15, wherein the processor is further configured to determine if image definition is acceptable.

25. The biometric scanner of claim 15, wherein the camera is further configured to apply a companding curve to a captured biometric image.

26. A system controller for use in a biometric scanner,

wherein said system controller performs an image darkness test on a biometric image to determine if the biometric image results in an acceptable image darkness level, and

wherein said system controller performs an image definition test on a biometric image to determine if the biometric image results in an acceptable image definition level.