Dithered focus evaluation

• US 8,164,682 B2
• Filed: 10/14/2008
• Issued: 04/24/2012
• 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.
• Primary Examiner(s): Perkey, W. B.
• Assistant Examiner(s): Chang, Fang-Chi
• Application Number:
  US12/250,589
• Publication Number:
  US 20100091169A1
• Time in Patent Office: 1,288 Days
• Field of Search: 348/349, 396/79
• US Class Current: 348/349
• 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 images with different focus settings, wherein the method comprises:

capturing a first set of one or more autofocus images with a first focus setting;

capturing a first video image with a second focus setting after capturing the first set;

capturing a second set of one or more autofocus images with a third focus setting, wherein the second focus setting is between the first and third focus settings and wherein the second set is captured after capturing the first video image;

evaluating a difference in focus quality between the first and second sets of autofocus images;

adjusting a fourth focus setting for a second video image based on the difference in focus quality between the first and second sets of autofocus images; and

capturing the second video image using the adjusted fourth focus setting.

2. The method of claim 1, wherein the first and the third focus settings are selected to effect substantially a same amount of defocus as compared to the second focus setting, but in opposite directions.

3. The method of claim 2, wherein adjusting the focus setting for the second video image comprises:

selecting the second focus setting used to capture the first video image when the difference in focus quality between the first and second sets of autofocus images is below a predetermined threshold; and

adjusting the fourth focus setting used to capture the second video image in the direction toward the first and second focus settings for the first and second sets of the autofocus images based on which of the first and second sets of the autofocus images is evaluated to have a better focus quality.

4. An image capture device, comprising:

a focus lens;

a sensor located in the optical path of the focus lens;

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

the autofocus system to capture a first set of one or more autofocus images with a first focus setting;

the autofocus system to capture a first video image with a second focus setting after capturing the first set;

the autofocus system to capture a second set of one or more autofocus images with a third focus setting, wherein the second focus setting is between the first and third focus settings and wherein the second set is to be captured after the capture of the first video image; and

wherein the autofocus system further comprises;

a focus evaluation section to evaluate the difference in focus quality between the first and second sets of autofocus images;

a focus adjustment section responsive to the evaluation section to adjust a fourth focus setting for a second video image based on the difference in focus quality between the first and second sets of autofocus images; and

a memory to store the second video image captured using the adjusted fourth focus setting.

5. The system of claim 4, wherein the first and the third focus settings are selected to effect substantially a same amount of defocus as compared to the second focus setting, but in opposite directions.

6. The system of claim 5, wherein the autofocus system to adjust the focus setting for the second video image comprises:

the autofocus system to select the second focus setting used to capture the first video image when the difference in focus quality between the first and second sets of autofocus images is below a predetermined threshold; and

the autofocus system to adjust the fourth focus setting used to capture the second video image in the direction toward the first and second focus settings for the first and second sets of the autofocus images based on which of the first and second sets of the autofocus images is evaluated to have a better focus quality.

7. The system of claim 4, wherein the focus lens comprises one of:

a moveable focus lens having multiple different focusing positions for auto-focusing; and

a variable focus lens with variable focal length or variable optical power for focusing, wherein the variable focus lens is adjusted electronically instead of moving the focus lens, to provide multiple different focal lengths or multiple different optical powers for auto-focusing.

8. A method for auto focusing comprising:

capturing a first set of autofocus images with a first focus setting, the first set comprised of multiple images each with decreasing steps of optical power;

capturing a first video image with a second focus setting after capturing the first set;

capturing a second set of autofocus images with a third focus setting, the second set comprised of multiple images each with increasing steps of optical power, wherein the second set is captured after capturing the first video image;

evaluating a difference in focus quality between the first and second sets of autofocus images;

adjusting a fourth focus setting for a second video image based on the difference in focus quality between the first and second sets of autofocus images; and

capturing the second video image using the adjusted fourth focus setting.

9. The method of claim 8, wherein adjusting the fourth focus setting for the second video image further comprises making a decision as to whether a focus adjustment is needed for the second video image after capturing the first set of autofocus images, after capturing the first video image, and after capturing the second set of autofocus images.

10. A method for auto focusing comprising:

capturing a first autofocus image of a first set with a first focus optical power setting;

capturing a first video image with a second focus optical power setting after capturing the first autofocus image of the first set;

capturing a first autofocus image of a second set with a third focus optical power setting, wherein the first autofocus image of the second set is captured after capturing the first video image;

capturing a second video image with the second focus optical power setting used for the first video image;

capturing a second autofocus image of the first set with a fifth focus optical power setting;

capturing a third video image with the second focus optical power setting used for the first and second video images;

capturing a second autofocus image of the second set with a sixth focus optical power setting;

evaluating a difference in focus quality between the first and second sets;

adjusting a seventh focus optical power setting for a third video image based on the difference in focus quality between the first and second sets; and

capturing the third video image using the adjusted seventh focus optical power setting.

11. The method of claim 10, wherein the first and fifth focus optical power settings used to capture the first set are less than the third and sixth focus optical power settings used to capture the second set.

12. The method of claim 10:

wherein the first focus optical power setting used to capture the first image of the first set is greater than the fifth focus optical power setting used to capture the second image of the first set; and

wherein the sixth focus optical power setting used to capture the second image of the second set is greater than the third focus optical power setting used to capture the first image of the second set.

13. A method for auto focusing comprising:

capturing a first set of autofocus images, the first set comprising at least a first autofocus image of the first set captured at a first focus setting of decreased optical power and further comprising at least a second autofocus image of the first set captured at a second focus setting of increased optical power;

capturing a first video image with a third focus setting after capturing the first set;

capturing a second set of autofocus images, the second set comprising at least a first autofocus image of the second set captured at the first focus setting of decreased optical power used to capture the first autofocus image of the first set, wherein the second set further comprises at least a second autofocus image of the second set captured at the second focus setting of increased optical power used to capture the second autofocus image of the first set, and wherein the second set of autofocus images is captured after capturing the first video image;

evaluating a difference in focus quality between the first and second sets of autofocus images;

adjusting a fourth focus setting for a second video image based on the difference in focus quality between the first and second sets of autofocus images; and

capturing the second video image using the adjusted fourth focus setting.

14. The method of claim 13, wherein capturing the first and second sets of autofocus images comprises rapid captures of autofocus images with short exposure times and fast readout of the autofocus images from the image sensor.

15. The method of claim 13, wherein the first and second sets of autofocus images are captured through a focus lens that implements rapid changes in optical power at 0.01 seconds or less per a 1 diopter change.