DITHERED FOCUS EVALUATION

• US 20100091169A1
• Filed: 10/14/2008
• Published: 04/15/2010
• Est. Priority Date: 10/14/2008
• Status: Active Grant

• Current Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Original Assignee: Omnivision Technologies Incorporated (Will Semiconductor Co., Ltd. Shanghai)
• Inventors: Border, John N., Guidash, Robert M.
• Granted Patent: US 8,164,682 B2
• Time in Patent Office: Days
• US Class Current: 348/345
• CPC Class Codes: H04N 23/67 Focus control based on electronic image sensor signals
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

The invention utilizes an autofocus system (806) that is capable of very fast changes in focus over a relatively small portion of the focus range of the focusing system. When operating continuously in a repeating series of images or frames such as are found in preview mode or in video capture, autofocus images are captured before and after each video frame wherein the autofocus images have different focus settings than the images in the series. The autofocus images are then evaluated for focus quality to determine whether focus adjustments are needed.

Claims

1. A method for auto focusing an image capture device that can capture a series of images to be stored, comprising:

capturing an image for use in focus evaluation, said image is not one of the series of images to be stored and is captured between two of the images in the series of images to be stored;

evaluating the image used in the focus evaluation; and

adjusting the focus based on the image used in the focus evaluation if it is determined that the focus needs to be adjusted and using said adjusted focus on at least one of the series of images to be stored.

2. A method as defined in claim 1, wherein the image used for focus evaluation has a different focus setting than the series of images to be stored.

3. A method as defined in claim 1, wherein the evaluation of the image used in the focus evaluation occurs between a plurality of the series of images to be stored.

4. A method as defined in claim 2, wherein the image used for focus evaluation is comprised of sets of two or more images for focus evaluation captured between images in the series of images to be stored and the focus settings for the images used for focus evaluation includes adjusting the focus in one direction for a first set of images for focus evaluation and adjusting the focus in the opposite direction for a second set of images for focus evaluation.

5. A method as defined in claim 4, wherein the adjusting the focus in one direction is a multi-step process.

6. A method as defined in claim 5, wherein the adjusting the focus in one direction includes decreasing the optical power in a cyclic stepwise fashion.

7. A method as defined in claim 5, wherein the adjusting the focus in one direction includes increasing the optical power in a cyclic stepwise fashion.

8. A method as defined in claim 2, wherein adjusting the focus is a multi-step process, some of the steps in the process are increasing in optical power and some of the steps in the process are decreasing in optical power.

9. An image capture device, comprising:

a lens;

a sensor located in the optical path of the lens;

an autofocus system coupled to the lens for adjusting the focus of the lens, the autofocus system including;

a focus evaluation section used in evaluating an image used in focus evaluation, said image is not one of a series of images to be stored by the image capture device and is captured between two of the images in the series of images to be stored; and

a focus adjustment section responsive to the evaluation circuit for adjusting the focus of the lens based on the image used in the focus evaluation if it is determined that the focus needs to be adjusted and using said adjusted focus on at least one of the series of images to be stored.

10. An image capture device as defined in claim 9, wherein the image sensor includes panchromatic pixels.

11. An image capture device as defined in claim 9, wherein the autofocus system includes one of the following:

piezoelectric actuator, liquid lens, fluid lens, electroactive polymer lens or liquid crystal lens.

12. An image capture device as defined in claim 9, wherein the autofocus system includes a dual range focus system where a portion of the dual range focus system can be changed faster than the other portion.

13. An image capture device as defined in claim 9, wherein the image sensor includes windowing or binning on the image sensor.

14. An image capture device as defined in claim 9, wherein the image used for focus evaluation has a different focus setting than the series of images to be captured.

15. An image capture device as defined in claim 9, wherein the evaluation of the image used in the focus evaluation by the focus evaluation section occurs between a plurality of the series of images to be stored.

16. An image capture device as defined in claim 14, wherein the evaluation of the image used in the focus evaluation by the focus evaluation section is performed between two or more of the series of images to be stored and the evaluation includes adjusting the focus in one direction in one of the two or more of the series of images to be stored and in the opposite direction in the other of the two or more of the series of images to be stored.

17. An image capture device as defined in claim 16, wherein the adjusting the focus in one direction is a multi-step process.

18. An image capture device as defined in claim 17, wherein the adjusting the focus in one direction includes decreasing the optical power in a cyclic stepwise fashion.

19. An image capture device as defined in claim 17, wherein the adjusting the focus in one direction includes increasing the optical power in a cyclic stepwise fashion.

20. An image capture device as defined in claim 14, wherein adjusting the focus is a multi-step process, some of the steps in the process are increasing in optical power and some of the steps in the process are decreasing in optical power.