Latent fingerprint imaging system

• US 8,774,613 B1
• Filed: 03/14/2014
• Issued: 07/08/2014
• Est. Priority Date: 11/03/2010
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Miesak, Edward J.
• Primary Examiner(s): Perkey, WB
• Application Number:
  US14/210,996
• Time in Patent Office: 116 Days
• Field of Search: 396/15
• US Class Current: 396/15
• CPC Class Codes: G06V 40/13 Sensors therefor
• CPC Class Codes: H04N 5/30 Transforming light or analogous information into electric information scanning details H04N3/00; cameras or camera modules comprising electronic image sensors, or control thereof H04N23/00; circuitry of solid-state image sensors [SSIS] or control thereof H04N25/00

Abstract

This document relates to a latent fingerprint imaging system. The system includes a light source that illuminates a sample surface having a raw latent fingerprint. The system further includes an optical detector arranged to capture fluorescence instantaneously from gap portions of the sample surface between ridges of the latent fingerprint and use the fluorescence from the gap portions to generate image data of the latent fingerprint on the sample surface. The light from the light source has a wavelength that is greater than a propagation threshold wavelength so the light can propagate from the light source to the sample surface and is less than an absorption threshold wavelength so the light is mostly absorbed by material of the latent fingerprint.

Claims

1. A latent fingerprint imaging system, comprising:

a light source that illuminates a sample surface having a raw latent fingerprint, wherein the sample surface is at an ambient temperature;

an optical detector arranged relative to the light source to capture fluorescence instantaneously upon illumination of the sample surface at the ambient temperature from gap portions of the sample surface between ridges of the latent fingerprint and to use the fluorescence from the gap portions to generate image data of the latent fingerprint on the sample surface; and

wherein light from the light source has a wavelength that is greater than a propagation threshold wavelength such that the light is configured to propagate from the light source to the sample surface, and wherein the wavelength is less than an absorption threshold wavelength such that the light is mostly absorbed by material of the latent fingerprint on the sample surface.

2. The system of claim 1, further comprising an image processor that analyzes said generated image data to verify that a contrast of the image data exceeds a minimum contrast threshold.

3. The system of claim 1, where the optical detector is aligned normal to said sample surface and wherein said light source is aligned at a non-normal angle to said sample surface.

4. The system of claim 1, wherein said light source is one of a flash lamp and a laser.

5. The system of claim 4, further comprising:

at least one mirror with a reflective coating to filter out wavelengths from the flash lamp other than wavelengths greater than the propagation threshold wavelength and less than the absorption threshold wavelength; and

a baffle configured to reduce scattering of the filtered wavelengths of light from the at least one mirror incident on the sample surface.

6. The system of claim 1, wherein the propagation threshold wavelength is in a range of approximately 160-180 nm, and wherein the absorption threshold wavelength is in a range of approximately 180-200 nm.

7. The system of claim 6, wherein the wavelength is in a range of approximately 200-213 nm.

8. The system of claim 6, wherein the wavelength is approximately 193 nm.

9. The system of claim 2, wherein said image processor is configured to:

determine the contrast based on a ratio of an intensity of an image pixel of the sample surface between the ridges of the fingerprint to an intensity of an image pixel of the ridges of the fingerprint;

compare the image contrast to a signal to noise ratio (SNR) of the optical detector; and

determine whether the image contrast exceeds the minimum contrast threshold, based on the comparison of the image contrast with the SNR.

10. The system of claim 9, wherein the image processor is configured to determine that the image contrast exceeds the minimum contrast threshold, based on the image contrast being at least twice the SNR of the optical detector.

11. A latent fingerprint imaging system, comprising:

a light source configured to output light with a wavelength that is greater than a propagation threshold wavelength such that the light can propagate a maximum distance and less than an absorption threshold wavelength such that most of the light is absorbed by fingerprint material;

wherein the light source is positioned to illuminate a sample surface having a raw latent fingerprint with the light, said sample surface separated from the light source by a distance that is less than the maximum distance; and

an optical detector arranged relative to the light source such that the optical detector captures fluorescence from gap portions of the sample surface between ridges of the latent fingerprint and uses the fluorescence of the gap portions to generate image data of the latent fingerprint on the sample surface.

12. The system of claim 11, wherein the sample surface is at an ambient temperature during the capture of fluorescence from the sample surface by the optical detector.

13. The system of claim 11, further comprising an image processor that analyzes said generated image data to verify that a contrast of the image data exceeds a minimum contrast threshold.

14. The system of claim 11, where the optical detector is aligned approximately normal to said sample surface and wherein said light source is aligned at a non-normal angle to said sample surface.

15. The system of claim 11, wherein the propagation threshold wavelength is in a range of approximately 160-180 nm, and wherein the absorption threshold wavelength is in a range of approximately 180-200 nm.

16. The system of claim wherein the light source is a flash lamp, said system further comprising:

at least one mirror with a reflective coating to filter out wavelengths from the flash lamp other than wavelengths greater than the propagation threshold wavelength and less than the absorption threshold wavelength; and

a baffle configured to reduce scattering of the filtered wavelengths of the light from the at least one mirror incident on the sample surface.

17. A method for imaging latent fingerprints, comprising:

outputting light from a light source with a wavelength that is greater than a propagation threshold wavelength such that the light can propagate a maximum distance and less than an absorption threshold wavelength such that most of the light is absorbed by fingerprint material;

positioning the light source to be separated by less than the maximum distance from a sample surface at an ambient temperature and having a raw latent fingerprint;

illuminating the sample surface and the fingerprint with the light;

instantaneously capturing fluorescence from gap portions of the sample surface between ridges of the latent fingerprint with an optical detector; and

generating image data with the fluorescence of the latent fingerprint on the sample surface.

18. The method of claim 17, further comprising analyzing said generated image data to verify that a contrast of the image data exceeds a minimum contrast threshold with an image processor.

19. The method of claim 17, further comprising:

filtering out wavelengths from the light source other than wavelengths greater than the propagation threshold wavelength and less than the absorption threshold wavelength with at least one mirror; and

reducing scattering of the filtered wavelengths of light from the at least one mirror incident on the sample surface.

20. The method of claim 18, wherein said analyzing step comprises:

determining the contrast based on a ratio of an intensity of an image pixel of the sample surface between the ridges of the fingerprint to an intensity of an image pixel of the ridges of the fingerprint;

comparing the image contrast to a signal to noise ratio (SNR) of the optical detector;

determining whether the image contrast exceeds the minimum contrast threshold, based on the comparison of the image contrast with the SNR.