Fingerprint-reading system

• US 6,459,804 B2
• Filed: 06/13/2001
• Issued: 10/01/2002
• Est. Priority Date: 06/14/1996
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Thomson-CSF (Thales SA)
• Inventors: Mainguet, Jean-François
• Primary Examiner(s): Couso, Yon J.
• Application Number:
  US09/878,966
• Publication Number:
  US 20010026636A1
• Time in Patent Office: 475 Days
• Field of Search: 382/124, 382/125, 382/126, 382/127, 382/135, 382/284, 382/323, 386/71
• US Class Current: 382/124
• CPC Class Codes: G06V 40/1306 non-optical, e.g. ultrasonic or capacitive sensing
• CPC Class Codes: G06V 40/1335 Combining adjacent partial images (e.g. slices) to create a composite input or reference pattern; Tracking a sweeping finger movement

Abstract

A fingerprint-reading system includes a fingerprint sensor having an active surface sensitive to the pressure and a temperature of a finger. The surface area of this sensor is far smaller than the surface area of the fingerprint to be read. The reading is done when the sensor and the finger are in contact and in a relative motion of sliding of the sensor and the finger with respect to each other. The system reconstitutes a complete image of the fingerprint from the partial images given by the sensor during this motion.

Claims

1. A process for reading a fingerprint, comprising:

obtaining a series of partial images of the fingerprint during a sliding relative motion between a finger and a sensor, said sensor having a sensing surface area smaller than a surface of area of an image on said sensor of said fingerprint to be read, and having several lines of sensing elements, each partial image partially overlapping a previous partial image, and

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images.

2. A process for reading a fingerprint according to claim 1, comprising:

determining a number of said sensitive elements having substantially identical signal values in an area of overlap between two successive partial images;

comparing said number to a predetermined number; and

adjusting a size of said area of overlap if said number is less than said predetermined number.

3. A process for reading a fingerprint according to claim 1, comprising:

generating first, second and third successive partial images;

matching said first and second successive images and form a first combined image; and

matching said third successive image with said first combined image to form a second combined image.

4. A process for reading a fingerprint according to claim 1, comprising:

generating first and second successive partial images; and

adjusting a relative position of said first and second partial images in at least two orthogonal directions to match said first and second partial images.

5. A process for reading a fingerprint according to claim 1, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

shifting a selected partial image with respect to a previous image to determine an optimal position of overlapping between said given partial image and said previous image; and

obtaining a new image from a shifted partial image and said previous image, said new image being larger than an image obtainable by said sensing surface.

6. A process for reading a fingerprint according to claim 1, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by shifting a partial image;

determining a correlation between a shifted partial image and a previous image;

determining a position of a shifted partial image which gives optimal correlation; and

constructing an image from said shifted partial image and said previous image.

7. A process for reading a fingerprint according to claim 1, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images, two successive overlapping partial images being such, due to said sliding movement, that said several lines of sensing elements receive different portions of an image of said fingerprint in said successive overlapping partial images.

8. A process for reading a fingerprint according to claim 1, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images, said correlation comprising effecting a displacement of one or two successive partial images towards the other to determine an optimal correlation in overlapping zones of said images; and

building from the two partial images an image larger than an image obtainable by the sensor.

9. A process for reading a fingerprint according to claim 1, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

finding a high correlation between a first zone of pixels of one partial image and another, different, zone of pixels of another partial image; and

building from said two partial images an image larger than said one and said other partial image, said larger image comprising;

a) said one partial image, and

b) said other partial image disclosed from an amount corresponding to a difference in position of said first and second zone of pixels in said sensing surface, said difference due to said sliding movement.

10. process for reading a fingerprint, comprising:

obtaining a series of partial images of the fingerprint during a sliding relative motion between a finger and a sensor, said sensor having several lines of sensing elements and having a sensing surface area capable of encompassing not more than a small portion of the fingerprint to be read, each partial image formed on said sensing surface area during said sliding movement corresponding to a different part of the fingerprint partially overlapping a previous part; and

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images.

12. A process for reading a fingerprint according to one of claims 10 and 11, comprising:

determining a number of said sensitive elements having substantially identical signal values in an area of overlap between two successive partial images;

comparing said number to a predetermined number; and

adjusting a size of said area of overlap if said number is less than said predetermined number.

13. A process for reading a fingerprint according to one of claims 10 and 11, comprising:

generating first, second and third successive partial images;

matching said first and second successive images and form a first combined image; and

matching said third successive image with said first combined image to form a second combined image.

14. A process for reading a fingerprint according to one of claims 10 and 11, comprising:

generating first and second successive partial images; and

adjusting a relative position of said first and second partial images in at least two orthogonal directions to match said first and second partial images.

15. A process for reading a fingerprint according to one of claims 10 and 11, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

shifting a selected partial image with respect to a previous image to determine an optimal position of overlapping between said given partial image and said previous image; and

obtaining a new image from a shifted partial image and said previous image, said new image being larger than an image obtainable by said sensing surface.

16. A process for reading a fingerprint according to one of claims 10 and 11, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by shifting a partial image;

determining a correlation between a shifted partial image and a previous image;

determining a position of a shifted partial image which gives optimal correlation; and

constructing an image from said shifted partial image and said previous image.

17. A process for reading a fingerprint according to one of claims 10 and 11, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images, two successive overlapping partial images being such, due to said sliding movement, that said several lines of sensing elements receive different portions of an image of said fingerprint in said successive overlapping partial images.

18. A process for reading a fingerprint according to one of claims 10 and 11, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images, said correlation comprising effecting a displacement of one or two successive partial images towards the other to determine an optimal correlation in overlapping zones of said images; and

building from the two partial images an image larger than an image obtainable by the sensor.

19. A process for reading a fingerprint according to one of claims 10 and 11, wherein the step of reconstructing a global image of said fingerprint to be read comprises:

finding a high correlation between a first zone of pixels of one partial image and another, different, zone of pixels of another partial image; and

building from said two partial images an image larger than said one and said other partial image, said larger image comprising;

a) said one partial image, and

b) said other partial image disclosed from an amount corresponding to a difference in position of said first and second zone of pixels in said sensing surface, said difference due to said sliding movement.

11. A process for reading a fingerprint, comprising:

obtaining a series of partial images of the fingerprint during a sliding relative motion between a finger and a sensor in direct contact with the finger, said sensor having a sensing surface area smaller than a surface of area of an image on said sensor of said fingerprint to be read, and having several lines of sensing elements, each partial image partially overlapping a previous partial image, and

reconstructing a global image of said fingerprint to be read by correlation of overlapping partial images.