APPARATUS FOR CAPTURING A HIGH QUALITY IMAGE OF A MOIST FINGER

• US 20080273771A1
• Filed: 04/17/2008
• Published: 11/06/2008
• Est. Priority Date: 05/01/2007
• Status: Active Grant

• Current Assignee: Thales DIS France SAS (Thales SA)
• Original Assignee: 3M Cogent Incorporated (Thales SA)
• Inventors: Zhou, Fei, Wang, Ankuo, Hsieh, Ming, Chen, Wheshi
• Granted Patent: US 8,275,179 B2
• Time in Patent Office: Days
• 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 apparatus for capturing the image of a wet/moist fingerprint. The apparatus includes: a prism having an imaging plane on which a finger having valleys and ridges is place, a bottom plane parallel to the imaging plane and a reflective plane intercepting the imaging plane and intercepting the bottom plane at an angle α; a light source for generating a light with an incident angle of approximately 0° with respect to a surface normal of the imaging plane; and a lens for capturing light reflected from the reflective plane. The apparatus further includes an image sensor for generating an image of the valleys and ridges of the finger, wherein the reflective plane is arranged in such a way to meet the equation of α>45 +(a sin(n₁/n₂))/2, where n₁ is a refraction index of medium filled between the valleys of the finger and the imaging plane, and n₂ is refraction index of the prism.

Claims

1. A fingerprint image capturing apparatus comprising:

a prism having an imaging plane on which a finger having valleys and ridges is place, a bottom plane parallel to the imaging plane and a reflective plane intercepting the imaging plane and intercepting the bottom plane at an angle α

;

a light source for generating a light with an incident angle of approximately 0°

with respect to a surface normal of the imaging plane;

a lens for capturing light reflected from the reflective plane; and

an image sensor for generating an image of the valleys and ridges of the finger, wherein the reflective plane is arranged in such a way to meet the following equation;

α

>

45+(a sin(n₁/n₂))/2,

where n₁ is a refraction index of medium filled between the valleys of the finger and the imaging plane, and n₂ is refraction index of the prism.

2. The fingerprint image capturing apparatus of claim 1, wherein α

is approximately in the rage of 73°

to 80°

.

3. The fingerprint image capturing apparatus of claim 1, wherein n₁ is approximately equal to 1.33 for water, and n₂ is approximately equal to 1.76 for the prism.

4. The fingerprint image capturing apparatus of claim 1, further comprising a mirror placed between the lens and the image sensor.

5. The fingerprint image capturing apparatus of claim 1, further comprising an adjusting means for tilting the reflective plane to change the value of α

.

6. The fingerprint image capturing apparatus of claim 5, wherein the adjusting means is a knob or screw.

7. The fingerprint image capturing apparatus of claim 1, wherein the prism is made from glass.

8. The fingerprint image capturing apparatus of claim 1, wherein the prism is made from plastic.