System and method for counting ridges in a captured print image

1. A method for counting print ridges in a captured print image frame, comprising the steps of:

(A) traversing a pixel path through the captured print image frame;

(B) determining a hysteresis band for the pixel path;

(C) counting a number of crossings of the determined hysteresis band while traversing the pixel path; and

(D) determining a number of print ridges based on the counted number of hysteresis band crossings;

wherein the hysteresis band is defined by a hysteresis band first edge value and a hysteresis band second edge value, wherein step (B) comprises the steps of:

(1) measuring a first ridge pixel value peak for the pixel path;

(2) measuring a first valley pixel value peak for the pixel path;

(3) selecting a hysteresis band center pixel value between the first ridge pixel value peak and the first valley pixel value peak;

(4) calculating the hysteresis band first edge value by adding a delta value to the selected hysteresis band center pixel value; and

(5) calculating the hysteresis band second edge value by subtracting the delta value from the selected hysteresis band center pixel value.

2. The method of claim 1 , wherein step (D) comprises the step of:

dividing the counted number of hysteresis band crossings by two to determine the number of print ridges.

3. The method of claim 1 , further comprising the steps of:

(E) traversing a second pixel path across the captured print image frame; and

(F) repeating steps (C) and (D) using the second pixel path.

4. The method of claim 1 , further comprising the steps of:

(E) determining a second hysteresis band;

(F) traversing a second pixel path across the captured print image frame; and

(G) repeating steps (C) and (D) using the second determined hysteresis band and the second pixel path.

5. The method of claim 1 , further comprising the steps of:

(E) determining a second hysteresis band;

(F) traversing the pixel path across the captured print image frame a second time; and

(G) repeating steps (C) and (D) using the second determined hysteresis band and the second traversal of the pixel path.

6. The method of claim 1 , wherein step (B)(3) comprises the step of:

calculating an average pixel value of the first ridge pixel value peak and the first valley pixel value peak; and

setting the hysteresis band center pixel value to the calculated average pixel value.

7. The method of claim 1 , further comprising the step of:

calculating the delta value according to the following equation

delta value=|(first valley pixel value peak−first ridge pixel value peak)|/6.

8. The method of claim 1 , wherein step (A) comprises the step of:

detecting pixel values sequentially along the pixel path.

9. The method of claim 8 , wherein step (C) comprises the steps of:

detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band first edge value to the hysteresis band second edge value; and

detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band second edge value to the hysteresis band first edge value.

10. A method for counting fingerprint ridges, comprising the steps of:

(A) identifying a region of interest in a stored fingerprint image frame;

(B) determining a pixel path through the region of interest;

(C) traversing the determined pixel path;

(D) determining a hysteresis band for the determined pixel path;

(E) counting a number of crossings of the determined hysteresis band while traversing the determined pixel path;

(F) determining a number of fingerprint ridges based on the counted number of hysteresis band crossings; and

(G) storing the number of fingerprint ridges determined in step (F);

wherein the hysteresis band is defined by a hysteresis band first edge value and a hysteresis band second edge value, wherein step (D) comprises the steps of:

(1) measuring a first ridge pixel value peak for the pixel path;

(2) measuring a first valley pixel value peak for the pixel path;

(3) selecting a hysteresis band center pixel value between the first ridge pixel value peak and the first valley pixel value peak;

(4) calculating the hysteresis band first edge value by adding a delta value to the selected hysteresis band center pixel value; and

(5) calculating the hysteresis band second edge value by subtracting the delta value from the selected hysteresis band center pixel value.

11. The method of claim 10 , further comprising the step of:

(H) capturing a fingerprint image; and

(I) storing the captured fingerprint image to be accessed as the stored fingerprint image frame.

12. The method of claim 11 , further comprising the step of:

(J) evaluating the stored number of fingerprint ridges to determine a quality of the captured fingerprint image.

13. The method of claim 10 , further comprising the step of:

(H) repeating steps (B)-(G) at least one additional time.

14. The method of claim 10 , further comprising the step of:

(H) evaluating the stored number of fingerprint ridges to determine a quality of the stored fingerprint image frame.

15. The method of claim 10 , wherein step (F) comprises the step of:

dividing the counted number of hysteresis band crossings by two to determine the number of fingerprint ridges.

16. The method of claim 10 , wherein step (D)(3) comprises the step of:

calculating an average pixel value of the first ridge pixel value peak and the first valley pixel value peak; and

setting the hysteresis band center pixel value to the calculated average pixel value.

17. The method of claim 10 , further comprising the step of:

calculating the delta value according to the following equation

delta value=|(first valley pixel value peak−first ridge pixel value peak)|/6.

18. The method of claim 10 , wherein step (C) comprises the step of:

detecting pixel values sequentially along the determined pixel path.

19. The method of claim 18 , wherein step (E) comprises the steps of:

detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band first edge value to the hysteresis band second edge value; and

detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band second edge value to the hysteresis band first edge value.

20. A system for counting fingerprint ridges in a captured fingerprint image frame, comprising:

a ridge counter module that includes

means for traversing a pixel path through the captured fingerprint image frame,

means for determining a hysteresis band for the pixel path;

means for counting a number of crossings of the determined hysteresis band while traversing the pixel path, and

means for determining a number of fingerprint ridges based on the counted number of hysteresis band crossings;

wherein the hysteresis band is defined by a hysteresis band first edge value and a hysteresis band second edge value, said hysteresis band determining means comprises:

means for measuring a first ridge pixel value peak for the pixel path;

means for measuring a first valley pixel value peak for the pixel path;

means for selecting a hysteresis band center pixel value between the first ridge pixel value peak and the first valley pixel value peak;

means for calculating the hysteresis band first edge value by adding a delta value to the selected hysteresis band center pixel value; and

means for calculating the hysteresis band second edge value by subtracting the delta value from the selected hysteresis band center pixel value.

21. The system of claim 20 , wherein said means for determining a number of fingerprint ridges comprises:

means for dividing the counted number of hysteresis band crossings by two to determine the number of fingerprint ridges.

22. The system of claim 20 , further comprising:

a camera that captures a fingerprint image and outputs said captured fingerprint image frame.

23. The system of claim 22 , further comprising:

a memory that stores said captured fingerprint image frame, and is accessible by said ridge counter module.

24. The system of claim 22 , further comprising:

a platen that has a finger application area.

25. The system of claim 24 , further comprising:

an illumination source that provides light to illuminate said finger application area to produce said fingerprint image.

26. The system of claim 25 , further comprising:

an optical system that directs said light to said camera.

27. The system of claim 24 , further comprising:

a controller that includes said ridge counter module and controls said illumination source and said camera.

28. The system of claim 20 , wherein said means for selecting a hysteresis band center pixel value comprises:

means for calculating an average pixel value of the first ridge pixel value peak and the first valley pixel value peak; and

means for setting the hysteresis band center pixel value to the calculated average pixel value.

29. The system of claim 20 , further comprising:

means for calculating the delta value according to the following equation

delta value=|(first valley pixel value peak−first ridge pixel value peak)|/6.

30. The system of claim 20 , wherein said means for traversing a pixel path comprises:

means for detecting pixel values sequentially along the pixel path.

31. The system of claim 30 , wherein said means for counting a number of crossings comprises:

means for detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band first edge value to the hysteresis band second edge value; and

means for detecting a hysteresis band crossing when sequentially detected pixel values range from the hysteresis band second edge value to the hysteresis band first edge value.