System and method to autofocus assisted by autoexposure control

• US 8,149,323 B2
• Filed: 12/18/2008
• Issued: 04/03/2012
• Est. Priority Date: 12/18/2008
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Li, Jingqiang, Velarde, Ruben M., Hung, Szepo R.
• Primary Examiner(s): SELBY, GEVELL V
• Application Number:
  US12/338,147
• Publication Number:
  US 20100157136A1
• Time in Patent Office: 1,202 Days
• Field of Search: 348/222.1, 348/229.1, 348/345, 348/362
• US Class Current: 348/345
• 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 23/72 Combination of two or more compensation controls
• CPC Class Codes: H04N 23/73 by influencing the exposure time

Abstract

In a particular embodiment, a method is disclosed that includes comparing a frame rate of image capture by an image sensor to a frame rate threshold at an image capture device. The method also includes when the frame rate is less than the frame rate threshold, increasing the frame rate to a modified frame rate that is greater than or at least equal to the frame rate threshold. The method further includes performing an autofocus operation on an image to be captured at the modified frame rate.

Claims

1. A method comprising:

comparing a frame rate of image capture by an image sensor to a frame rate threshold at an image capture device;

when the frame rate is less than the frame rate threshold, increasing the frame rate to a modified frame rate that is greater than or equal to the frame rate threshold;

decreasing an integration time and increasing an image signal gain at the image capture device to adjust an image brightness level before performing an autofocus operation on an image captured at the modified frame rate; and

performing an autofocus operation on the image captured at the modified frame rate.

2. The method of claim 1, wherein the frame rate threshold is a maximum frame rate for the image capture device and wherein the modified frame rate is approximately equal to the maximum frame rate.

3. The method of claim 1, wherein the modified frame rate is in a range of about 1.5 times the frame rate to about three times the frame rate.

4. The method of claim 1, wherein the modified frame rate is approximately two times the frame rate.

5. The method of claim 1, further comprising reducing an exposure index at the image capture device before performing the autofocus operation.

6. The method of claim 1, wherein the image capture device comprises one of a digital camera, a digital video camera, and a camera-phone.

7. The method of claim 1, further comprising reducing an integration time at the image capture device when the frame rate is not less than the frame rate threshold.

8. The method of claim 1, wherein the image comprises one or more pixels of image data and the autofocus operation on the image includes consideration of all of the one or more pixels of image data.

9. An image capture method comprising:

capturing a first image at a frame rate of image capture using a lens system coupled to an image sensor of an image capture device;

adjusting an image signal gain of an image signal output from the image sensor;

processing the adjusted image signal using a digital signal processor in the image capture device, the digital signal processor coupled to an autoexposure controller and to an autofocus device in the image capture device;

increasing the frame rate of image capture by the image sensor of the image capture device using the autoexposure controller when the frame rate is below a predetermined frame rate;

reducing an exposure time of the image sensor of the image capture device using the autoexposure controller after increasing the frame rate;

capturing a second image at the increased frame rate of image capture using the lens system coupled to the image sensor of the image capture device;

increasing the image signal gain to adjust a brightness level of the second image;

performing an autofocus operation using the autofocus device to adjust a lens position of the lens system to focus the second image; and

decreasing an autofocus latency by increasing the frame rate and increasing an autofocus accuracy by reducing the exposure time and increasing the image signal gain.

10. The image capture method of claim 9, further comprising determining the lens position corresponding to a highest image contrast of the second image.

11. The image capture method of claim 10, further comprising returning the frame rate, the exposure time, and the image signal gain to original values after the lens position is determined.

12. The image capture method of claim 9, further comprising reducing an exposure index at the image capture device using the autoexposure controller and increasing the image signal gain to adjust the brightness level of the image using the autoexposure controller.

13. The image capture method of claim 9, further comprising decreasing an integration time of integrating the image at the image sensor of the image capture device.

14. The image capture method of claim 9, further comprising reducing an integration time of integrating the image at the image sensor of the image capture device when the frame rate is not less than the predetermined frame rate.

15. The method of claim 9, wherein the second image comprises one or more pixels of image data and the autofocus operation on the second image includes consideration of all of the one or more pixels of image data.

16. An image capture device comprising:

an image sensor configured to capture an image comprising one or more pixels of image data;

an autoexposure control device configured to;

increase a frame rate of image capture by the image sensor to an increased frame rate when the frame rate is less than a frame rate threshold;

reduce an integration time of the image sensor to a reduced integration time when the frame rate is less than a frame rate threshold; and

increase an image signal gain of an image signal output from the image sensor to an increased image signal gain to adjust an image brightness level when the frame rate is less than a frame rate threshold; and

an autofocus device configured to perform an autofocus operation on the image using the increased frame rate, the reduced integration time, and the increased image signal gain.

17. The image capture device of claim 16, wherein the autoexposure control device is further configured to reduce an exposure index of the image sensor.

18. The image capture device of claim 16, wherein the autofocus device is further configured to perform the autofocus operation on the image by considering all of the one or more pixels of image data representing the image.

19. An image capture device comprising:

an image sensor configured to capture an image comprising one or more pixels of image data;

means for controlling an autoexposure configured to;

increase a frame rate of image capture by the image sensor to an increased frame rate when the frame rate is less than a frame rate threshold;

reduce an integration time of the image sensor to a reduced integration time when the frame rate is less than a frame rate threshold; and

increase an image signal gain of an image signal output from the image sensor to an increased image signal gain to adjust an image brightness level when the frame rate is less than a frame rate threshold; and

means for performing an autofocus operation on the image using the increased frame rate, the reduced integration time, and the increased image signal gain.

20. A portable device including a camera, the portable device comprising:

an image sensor configured to capture an image comprising one or more pixels of image data;

an autoexposure control device configured to;

increase a frame rate of image capture of the image sensor to a modified frame rate when the frame rate is less than a frame rate threshold;

reduce an integration time at the camera to a reduced integration time when the frame rate is less than a frame rate threshold; and

increase an image signal gain at the camera to an increased image signal gain to adjust an image brightness level when the frame rate is less than a frame rate threshold; and

means for performing an autofocus operation on an image captured at the modified frame rate, the reduced integration time, and the increased image signal gain.

21. The portable device of claim 20, wherein the autoexposure control device and the means for performing the autofocus operation are disposed in an application chipset within the portable device.

22. The portable device of claim 20, wherein the autoexposure control device and the means for performing the autofocus operation are disposed in an image sensor of the portable device.

23. The image capture device of claim 20, wherein the means for performing an autofocus operation is further configured to perform the autofocus operation on the image by considering all of the one or more pixels of image data representing the image.

24. A computer-readable medium including computer executable instructions that are operative to cause a computer to:

increase a frame rate of capture of an image by an image sensor to a modified frame rate that is greater than or at least equal to a frame rate threshold at an image capture device;

reduce an exposure time of the image sensor at the image capture device;

increase an image signal gain of an image signal output from the image sensor at the image capture device; and

reduce an integration time of integrating the image at the image sensor of the image capture device when the frame rate is not less than the frame rate threshold.

25. The computer-readable medium of claim 24, wherein the frame rate threshold is a maximum frame rate for the image capture device.