Image sensor with integrated region of interest calculation for iris capture, autofocus, and gain control

• US 9,131,141 B2
• Filed: 05/12/2009
• Issued: 09/08/2015
• Est. Priority Date: 05/12/2008
• Status: Active Grant

• Current Assignee: Princeton Identity Inc.
• Original Assignee: SRI International, Inc.
• Inventors: Tinker, Michael, Ackerman, David Alan, Kolczynski, Raymond, Bergen, James
• Primary Examiner(s): Joo, Joshua
• Application Number:
  US12/464,369
• Publication Number:
  US 20090278922A1
• Time in Patent Office: 2,310 Days
• Field of Search: 348/61, 348 77- 78
• US Class Current: 1/1
• CPC Class Codes: G06V 10/255 Detecting or recognising potential candidate objects based on visual cues, e.g. shapes
• CPC Class Codes: G06V 40/193 Preprocessing; Feature extraction
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 23/673 based on contrast or high frequency components of image signals, e.g. hill climbing method
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

An iris recognition system and method for operating same is disclosed. The iris recognition system includes an image sensor, a buffer, a comparator, autofocus logic, and gain control logic. The image sensor is configured to obtain at least one image from a camera. The buffer communicatively connected to the image sensor stores values associated with the pixels in the image sensor. The comparator communicatively connected to the buffer obtains a coarse segmentation of an iris of a subject. The autofocus logic for adjusts the focus of a lens associated with the camera. The gain control logic adjusts the gain of the image sensor. The functions of obtaining a coarse segmentation, adjusting the focus of the lens, and adjusting the gain are based on the locations of the pixels with the highest value in the image sensor as stored in the buffer.

Claims

1. A method for locating and identifying an iris in an image taken by a camera associated with an iris recognition system comprising an image sensor and a plurality of illuminators, comprising the steps of:

illuminating a subject;

capturing at least one image of the subject wherein the image comprises a plurality of pixels;

determining a brightness value for each of the plurality of pixels;

identifying specularities in the iris from the brightness values for each of the plurality of pixels, the specularities defining a brightest pixel set;

determining a location corresponding to each pixel in the brightest pixel set; and

identifying the iris in the at least one image from the location of each pixel in the brightest pixel set and a pattern formed by the brightest pixel set.

2. The method of claim 1, wherein the system further comprises a buffer communicatively connected to the image sensor, and a comparator communicatively connected to the buffer, and wherein the method further comprises:

storing addresses and brightness of each of the plurality of pixels in the buffer;

sending a current stored value of a pixel to the comparator;

comparing with the comparator the stored value to a current smallest brightness value in the buffer, wherein if the current stored value is greater than the current smallest brightness value, then replacing the current smallest brightness value with the current stored value in the buffer; and

repeating the sending and comparing for each of the pixels in the image.

3. The method of claim 2, further comprising:

prior to storing addresses, translating linear addresses into row and column addresses for the image sensor;

scanning all pixels on the image sensor;

selecting from among the scanned pixels the addresses and brightness values corresponding to the brightest pixel set; and

storing the selected addresses and brightness values in the buffer.

4. The method of claim 2, further comprising sending the addresses of the pixels in the brightest pixel set from the buffer to the image sensor for output to a display.

5. A method for autofocusing a camera having a lens and having a focus mechanism, the camera being associated with an iris recognition system comprising an image sensor and a plurality of illuminators, comprising:

illuminating a subject with the plurality of illuminators;

capturing at least one image of the subject with the image sensor;

determining brightest pixels in the image sensor;

determining a plurality of values associated with the brightest pixels in the image sensor;

refocusing the camera based on the brightest pixels and a pattern formed by a brightest pixel set in the image sensor; and

repeating the capturing, the determining the brightest pixels, the determining a plurality of values and the refocusing until a change in a highest pixel value among two successive scans is less than a predetermined threshold value to autofocus the camera for locating the iris.

6. The method of claim 5, wherein refocusing and repeating further comprise:

repeating the capturing and the determining the brightest pixels to obtain a second plurality of values associated with the brightest pixels; and

wherein if the highest value from among the second plurality of values is greater than a highest value from among plurality of values determined prior to the second plurality of values, then

signaling the lens to change focus in a predetermined direction and

repeating the capturing and the determining the brightest pixels to obtain a second plurality of values,

otherwise, signaling the lens to change focus in a direction opposite to the predetermined direction and repeating the capturing and the determining the brightest pixels.

7. The method of claim 5, wherein the highest pixel value is associated with a specularity generated in the at least one image by the plurality of illuminators.

8. A method for providing automatic gain control for an image sensor associated with an iris recognition system comprising an image sensor and a plurality of illuminators, comprising:

illuminating a subject with the plurality of illuminators;

capturing at least one image of the subject with the image sensor;

determining brightest pixels in the image;

determining a plurality of values associated with the brightest pixels in the image to locate an iris in the image of the subject;

adjusting gain associated with the image sensor using the brightest pixels in the image sensor, wherein the adjusting is performed at the image sensor, wherein the adjusting results in the plurality of values being between predetermined minimum and maximum threshold values; and

repeating the capturing, the determining brightest pixels, the determining a plurality of values, and the adjusting until a highest value of the plurality of values is between the predetermined minimum and maximum threshold values.

9. The method of claim 8, wherein the adjusting and repeating further comprise:

if the highest value of the plurality of values is above a maximum threshold, reducing gain associated with the image sensor; and

repeating the capturing, the determining brightest pixels, the determining a plurality of values, and the reducing until a highest value of the plurality of values is below the maximum threshold;

otherwise

if the highest value of the plurality of values is below a minimum threshold, increasing gain associated with the image sensor; and

repeating the capturing, the determining brightest pixels, the determining a plurality of values, and the increasing until a highest value of the plurality of values is above the minimum threshold.

10. The method of claim 8, wherein the minimum threshold value is a minimum predetermined value less than the maximum threshold value.

11. An iris recognition system, comprising:

an image sensor configured to receive at least one image comprising a plurality of pixels from a camera comprising a lens;

a buffer communicatively connected to the image sensor for storing values associated with the plurality of pixels; and

a comparator circuit communicatively connected to the buffer configured to locate and identify an iris of a subject from the stored values;

wherein locating and identifying the iris of the subject uses a location of each pixel in a brightest pixel set determined by the comparator circuit and a pattern formed by the brightest pixel set.

12. The system of claim 11, further comprising autofocus logic circuitry to adjust focus of a lens associated with the camera, wherein adjusting the focus of the lens is based on a location of each pixel in a brightest pixel set.

13. The system of claim 12, further comprising gain control logic circuitry for adjusting gain of the image sensor, wherein adjusting the gain is based on a location of each pixel in a brightest pixel set.

14. The system of claim 11, further comprising a plurality of illuminators communicatively connected to the image sensor for illuminating a subject.

15. The system of claim 14, wherein each of the plurality of illuminators is a near infrared (NIR) strobed sensor.

16. The system of claim 15, wherein each of illuminators are configured to strobe light with a wavelength of 850 nm.

17. The system of claim 11, wherein the image sensor is one of a charge coupled device (CCD) and a complementary metal oxide semiconductor (CMOS) image sensor.

18. The system of claim 11, wherein the system is integrated on an integrated circuit.

19. The system of claim 12, wherein the autofocus logic circuitry is to refocus the camera until a change in a highest pixel value of the at least one image among two successive scans taken by the image sensor and stored in the buffer is less than a predetermined threshold value.

20. The system of claim 13, wherein the gain control logic circuitry is to adjust gain until a highest value of the plurality of pixels taken by the image sensor and stored in the buffer is between minimum and maximum threshold values.