System and method for determining if a fingerprint image contains an image portion representing a dry fingerprint impression

• US 5,995,640 A
• Filed: 10/23/1996
• Issued: 11/30/1999
• Est. Priority Date: 10/23/1996
• Status: Expired due to Term

• Current Assignee: Pendragon Networks LLC (Pendrell Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Bolle, Rudolf Maarten, Pankanti, Sharathchandra Umapatirao, Yao, Yi-Sheng
• Primary Examiner(s): Kelley, Christopher S
• Assistant Examiner(s): CHAWAN, SHEELA C
• Application Number:
  US08/735,721
• Time in Patent Office: 1,133 Days
• Field of Search: 382/124, 382/125, 382/126, 382/116, 382/274, 382/266, 382/263, 382/272, 283/68, 283/69, 283/78, 356/71, 340/825.34
• 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 fingerprint image is divided into blocks of pixels. The blocks are also determined to be within the foreground or background of the image. A dryness process determines a mean intensity of pixels within each foreground block, a second mean intensity of pixels for those pixels whose intensities are smaller than the mean intensity, a standard deviation of intensities of all pixels within the respective foreground block, and a contrast measure being a function of a first ratio of the second mean intensity to the standard deviation. A comparator that determines that the foreground block is a dry block if the contrast measure is larger than a dryness threshold and that the image is a dry image if a second ratio of the number of dry blocks to total number of foreground blocks is larger than a third dryness threshold.

Claims

1. A system for determining whether fingerprint images contain dry impressions comprising:

a computer comprising at least one central processing unit, at least one memory, and at least one input device;

at least one fingerprint image having a foreground and a background and being acquired by the input device and stored in the at least one memory, the at least one fingerprint image further comprising a plurality of blocks of pixels;

a dryness process that operates on said computer for determining a mean intensity of pixels within each foreground block of pixels, for determining a second mean intensity of pixels for those pixels within the respective foreground block of pixels whose intensities are less than the mean intensity, and for determining a standard deviation of intensities of all pixels within the respective foreground block of pixels, wherein a contrast measure is a function of a first ratio of the determined second mean intensity to the determined standard deviation; and

a comparator that determines that the foreground block of pixels is a dry block if the contrast measure is greater than a dryness threshold, and that further determines that the fingerprint image is a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold.

2. A system, as in claim 1, where the contrast measure is less than the dryness threshold, and wherein the corresponding foreground block is identified as being a dry block if a variation in the contrast measure of two or more neighboring blocks is greater than a third dryness threshold, the neighboring blocks being adjacent to the corresponding foreground block.

3. A system, as in claim 1, wherein said at least one input device is comprised of at least one of a camera, an image scanner, and a second computer connected to a network in common with the system.

4. A system, as in claim 1, where the blocks of pixels comprise down-sampled subsets of pixels from an area on an original fingerprint image.

5. A system, as in claim 1, where the foreground block is not identified as a dry block, but wherein the image is identified as failing a quality criteria.

6. A system, as in claim 1, where the second mean intensity is comprised of a mean ridge intensity.

8. A system, as in claim 1, where the dryness threshold is 4.5.

10. A system, as in claim 2, where the third dryness threshold is 3.5.

12. A system, as in claim 1, where the second dryness threshold is 0.4.

7. A system for determining whether fingerprint images contain dry impressions comprising:

a computer comprising at least one central processing unit, at least one memory, and at least one input device;

at least one fingerprint image having a foreground and a background and being acquired by the input device and stored in the at least one memory, the at least one fingerprint image further comprising a plurality of blocks of pixels;

a dryness process that operates on said computer for determining a mean intensity of pixels within each foreground block of pixels, for determining a second mean intensity of pixels for those pixels within the respective foreground block of pixels whose intensities are less than the mean intensity, and for determining a standard deviation of intensities of all pixels within the respective foreground block of pixels, wherein a contrast measure is a function of a first ratio of the determined second mean intensity to the determined standard deviation; and

a comparator that determines that the foreground block of pixels is a dry block if the contrast measure is greater than a dryness threshold, and that further determines that the fingerprint image is a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold, where the dryness threshold is greater than 4.0.

9. A system for determining whether fingerprint images contain dry impressions comprising:

a computer comprising at least one central processing unit, at least one memory, and at least one input device;

at least one fingerprint image having a foreground and a background and being acquired by the input device and stored in the at least one memory, the at least one fingerprint image further comprising a plurality of blocks of pixels;

a dryness process that operates on said computer for determining a mean intensity of pixels within each forearound block of pixels, for determining a second mean intensity of pixels for those pixels within the respective foreground block of pixels whose intensities are less than the mean intensity, and for determining a standard deviation of intensities of all pixels within the respective foreground block of pixels, wherein a contrast measure is a function of a first ratio of the determined second mean intensity to the determined standard deviation; and

a comparator that determines that the foreground block of pixels is a dry block if the contrast measure is greater than a dryness threshold, and that further determines that the fingerprint image is a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold.

where the contrast measure is less than the dryness threshold, and wherein the corresponding foreground block is identified as being a dry block if a variation in the contrast measure of two or more neighboring blocks is greater than a third dryness threshold, the neighboring blocks being adjacent to the corresponding foreground block, where the third dryness threshold is between 2 and 4.0.

11. A system for determining whether fingerprint images contain dry impressions comprising:

a computer comprising at least one central processing unit, at least one memory, and at least one input device;

at least one fingerprint image having a foreground and a background and being acquired by the input device and stored in the at least one memory, the at least one fingerprint image further comprising a plurality of blocks of pixels;

a dryness process that operates on said computer for determining a mean intensity of pixels within each foreground block of pixels, for determining a second mean intensity of pixels for those pixels within the respective foreground block of pixels whose intensities are less than the mean intensity, and for determining a standard deviation of intensities of all pixels within the respective foreground block of pixels, wherein a contrast measure is a function of a first ratio of the determined second mean intensity to the determined standard deviation; and

a comparator that determines that the foreground block of pixels is a dry block if the contrast measure is greater than a dryness threshold, and that further determines that the fingerprint image is a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold, where the second dryness threshold is greater than or equal to 0.4.

13. A method of detecting a dry fingerprint image comprising the steps of:

selecting at least one foreground block of pixels in a fingerprint image;

determining a mean intensity of pixels for each selected foreground block of pixels;

determining a second mean intensity of all the pixels of the selected foreground block that have an intensity below the determined mean intensity;

determining a standard deviation of the intensities of pixels of the selected foreground block;

marking the foreground block as a dry block if a contrast measure is greater than a dryness threshold, the contrast measure being a function of a ratio of the determined second mean intensity to the determined standard deviation; and

identifying the fingerprint image as a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold.

14. A method, as in claim 13, where the contrast measure is less than the dryness threshold, and wherein the corresponding foreground block is identified as being a dry block if a variation in the contrast measure of two or more neighboring blocks is greater than a third dryness threshold, the neighboring blocks being adjacent to the corresponding foreground block.

15. A method for processing an image of a fingerprint, comprising steps of:

obtaining an image of a fingerprint, the image being comprised of pixels;

processing the fingerprint image to partition the image into blocks of pixels each specified to be one of a background block or a foreground block;

further processing foreground blocks to obtain regions each comprised of set of contiguous foreground blocks wherein the pixels of a block exhibit a prominent directionality;

weighting blocks as a function of distance from a common reference point within the fingerprint image;

determining a quality measure for the fingerprint image by computing a ratio of a summation of total weights of blocks exhibiting a prominent directionality to a summation of the weights of the foreground blocks; and

directing further processing of the fingerprint image based on the determined quality measure by comparing the determined quality measure to a quality threshold;

wherein if the determined quality measure is less than the quality threshold, the step of directing further processing is comprised of a step of performing a dryness analysis of the fingerprint image;

wherein the dryness analysis comprises steps of,

determining a mean intensity of pixels for individual ones of foreground blocks of pixels;

determining a second mean intensity of pixels for the individual ones of the foreground blocks that have an intensity below the determined mean intensity;

determining a standard deviation of the intensities of pixels for the individual ones of the foreground blocks;

marking a given foreground block as being a dry block if a contrast measure is greater than a dryness threshold, the contrast measure being a function of a ratio of the determined second mean intensity to the determined standard deviation; and

identifying the fingerprint image as a dry image if a second ratio of the number of dry blocks to a total number of foreground blocks is larger than a second dryness threshold.

16. A method as in claim 15, where the contrast measure is less than the dryness threshold, and wherein the corresponding foreground block is identified as being a dry block if a variation in the contrast measure of two or more neighboring blocks is greater than a third dryness threshold, the neighboring blocks being adjacent to the corresponding foreground block.

17. A method as in claim 16, where the dryness threshold has a value between about 4.0 and about 5.0, where the second dryness threshold is approximately 0.4, and where the third dryness threshold has a value between about 2.0 and 4.0.

18. A method as in claim 15, wherein the common reference point is a centroid of the regions of foreground blocks.