Continuous autofocus mechanisms for image capturing devices

• US 8,786,761 B2
• Filed: 06/05/2009
• Issued: 07/22/2014
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Brunner, Ralph, Hayward, David
• Primary Examiner(s): Harrington, Alicia M
• Application Number:
  US12/479,728
• Publication Number:
  US 20100309364A1
• Time in Patent Office: 1,873 Days
• Field of Search: 348/345, 348/349, 348351-353
• US Class Current: 348/349
• CPC Class Codes: G03B 13/36 Autofocus systems
• CPC Class Codes: H04M 2250/12 including a sensor for measuring a physical value, e.g. temperature or motion telephones including GPS signal receivers H04M2250/10
• CPC Class Codes: H04M 2250/52 including functional features of a camera constructional features concerning the integration of cameras in portable phones H04M1/0264
• 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 23/68 for stable pick-up of the scene, e.g. compensating for camera body vibrations
• CPC Class Codes: H04N 23/6812 based on additional sensors, e.g. acceleration sensors
• CPC Class Codes: H04N 5/772 the recording apparatus and the television camera being placed in the same enclosure

Abstract

At least certain embodiments described herein provide a continuous autofocus mechanism for an image capturing device. The continuous autofocus mechanism can perform an autofocus scan for a lens of the image capturing device and obtain focus scores associated with the autofocus scan. The continuous autofocus mechanism can determine an acceptable band of focus scores based on the obtained focus scores. Next, the continuous autofocus mechanism can determine whether a current focus score is within the acceptable band of focus scores. A refocus scan may be performed if the current focus score is outside of the acceptable band of focus scores.

Claims

1. A method to implement a continuous autofocus

mechanism for an image capturing device, the method comprising:

performing an autofocus scan that positions a lens of the image capturing device in a plurality of positions;

obtaining a plurality of focus scores with each focus score being associated with a respective lens position of the autofocus scan; and

determining an acceptable band of focus scores based on the obtained plurality of focus scores, wherein determining the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores, wherein determining the acceptable band of focus scores comprises determining a first derivative of a peak focus score value with respect to a first focus score value that is adjacent to the peak focus score value and determining a first derivative of the peak focus score value with respect to a second focus score value that is adjacent to the peak focus score value, wherein the first focus score value is associated with a different lens position than the second focus score value.

2. The method of claim 1, further comprising:

determining whether a frame is stable;

determining a current lens position and a current focus score associated with the frame if the frame is stable; and

determining whether the current focus score associated with the frame is within the acceptable band of focus scores.

3. The method of claim 2, further comprising:

setting the lens position to a new position in which the lens moves from the current position by a predetermined adjustment towards a lens position associated with the lens being focused near infinity if the current score is greater than the upper limit of the acceptable band of scores; and

starting a refocus scan at the new position.

4. The method of claim 1, wherein determining each of the lower limit and the upper limit of the acceptable band of focus scores is based on the peak focus score value, the acceptable band of focus scores, and a largest first derivative of the peak focus score value with respect to one of a plurality of focus score values adjacent to the peak focus score value.

5. The method of claim 1, wherein determining the acceptable band of focus scores further comprises determining a first derivative of the peak focus score value with respect to a third focus score value that is adjacent to the peak focus score value and determining a first derivative of the peak focus score value with respect to a fourth focus score value that is adjacent to the peak focus score value.

6. A method to implement a continuous autofocus mechanism for an image capturing device, the method comprising:

performing an autofocus scan that positions a lens of the image capturing device in a plurality of positions;

obtaining a plurality of focus scores with each focus score being associated with a respective lens position of the autofocus scan;

determining an acceptable band of focus scores based on the obtained plurality of focus scores, wherein determining the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores;

determining an intersection of the current score on a focus graph of focus scores versus lens positions if the current score is less than the lower limit of the acceptable band of scores;

estimating a lens position based on the intersection; and

starting a refocus scan, which is a new autofocus scan, at the lens position.

7. A method to implement a continuous autofocus mechanism for an image capturing device, the method comprising:

performing an autofocus scan that positions a lens of the image capturing device in a plurality of positions;

obtaining a plurality of focus scores with each focus score being associated with a respective lens position of the autofocus scan;

determining an acceptable band of focus scores based on the obtained plurality of focus scores;

determining whether a lens is focused close to infinity; and

setting a starting position that corresponds to the lens focused at infinity for a refocus scan if the lens is focused close to infinity.

8. A machine readable medium containing executable computer program instructions which when executed by a data processing system cause said system to perform a method, the method comprising:

performing an autofocus scan for a lens of the image capturing device;

obtaining a plurality of focus scores associated with the autofocus scan; and

determining an acceptable band of focus scores based on the obtained focus scores, wherein determining the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores, wherein determining the acceptable band of focus scores comprises determining a first derivative of a peak focus score value with respect to a first focus score value that is adjacent to the peak focus score value and determining a first derivative of the peak focus score value with respect to a second focus score value that is adjacent to the peak focus score value, wherein the first focus score value is associated with a different lens position than the second focus score value.

9. The medium of claim 8, the method further comprising:

determining whether a frame is stable;

determining a current lens position and a current focus score associated with the frame if the frame is stable; and

determining whether the current focus score associated with the frame is within the acceptable band of focus scores.

10. The medium of claim 8, wherein determining each of the lower limit and the upper limit of the acceptable band of focus scores is based on the peak focus score value, the acceptable band of focus scores, and a largest first derivative of the peak focus score value with respect to one of a plurality of focus score values adjacent to the peak focus score value.

11. The medium of claim 8, the method further comprising:

determining an intersection of the current score on a focus graph of focus scores versus lens positions if the current score is less than the lower limit of the acceptable band of scores;

estimating a lens position based on the intersection; and

starting a refocus scan, which is a new autofocus scan, at the lens position.

12. A machine readable medium containing executable computer program instructions which when executed by a data processing system cause said system to perform a method, the method comprising:

performing an autofocus scan for a lens of the image capturing device;

obtaining a plurality of focus scores associated with the autofocus scan; and

determining an acceptable band of focus scores based on the obtained focus scores, wherein determining the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores;

determining whether a frame is stable;

determining a current lens position and a current focus score associated with the frame if the frame is stable;

determining whether the current focus score associated with the frame is within the acceptable band of focus scores;

setting the lens position to a new position in which the lens moves from the current position by a predetermined adjustment towards a lens position associated with the lens being focused near infinity if the current score is greater than the upper limit of the acceptable band of scores; and

starting a refocus scan at the new position.

13. An image capturing device, comprising:

a storage device to store a plurality of captured images;

a lens to receive incident light associated with an image to be captured; and

a processing system coupled to the storage device, the processing system is configured to perform an autofocus scan, to obtain a plurality of focus scores associated with the autofocus scan; and

to determine an acceptable band of focus scores for the lens based on the obtained focus scores, wherein to determine the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores, wherein to determine the acceptable band of focus scores comprises determining a first derivative of a peak focus score value with respect to a first focus score value that is adjacent to the peak focus score value and determining a first derivative of the peak focus score value with respect to a second focus score value that is adjacent to the peak focus score value, wherein the first focus score value is associated with a different lens position than the second focus score value.

14. The device of claim 13, wherein the processing system is further configured:

to determine whether a frame is stable;

to determine a current lens position and a current focus score associated with the frame if the frame is stable; and

to determine whether the current focus score associated with the frame is within the acceptable band of focus scores.

15. The device of claim 13, wherein determining each of the lower limit and the upper limit of the acceptable band of focus scores is based on the peak focus score value, the acceptable band of focus scores, and a largest first derivative of the peak focus score value with respect to one of a plurality of focus score values adjacent to the peak focus score value.

16. The device of claim 13, further comprising:

a motion sensor to determine motion information for the device.

17. The device of claim 16, wherein the motion sensor comprises an accelerometer.

18. The device of claim 13, wherein the processing system is configured to determine whether a refocus scan is needed and to start a refocus scan.

19. The device of claim 18, wherein the processing system is configured to perform the refocus scan by positioning the lens in a plurality of positions.

20. An image capturing device, comprising:

a storage device to store a plurality of captured images;

a lens to receive incident light associated with an image to be captured; and

a processing system coupled to the storage device, the processing system is configured to perform an autofocus scan, to obtain a plurality of focus scores associated with the autofocus scan; and

to determine an acceptable band of focus scores for the lens based on the obtained focus scores, wherein to determine the acceptable band of focus scores comprises determining a lower limit and an upper limit of the acceptable band of focus scores, wherein the processing system is configured to determine whether a refocus scan is needed and to start a refocus scan, wherein the processing system is configured to perform the refocus scan by positioning the lens in a plurality of positions, wherein the processing system is configured to detect that the lens has moved past a predetermined position and to abort the refocus scan without moving the lens to the remaining positions of the refocus scan.

21. A method, comprising:

determining motion information for an image capturing device using one or more motion sensors;

determining whether the device is moving based on the motion information; and

filtering a plurality of focus scores based on the motion information, wherein each focus score is filtered by applying a dampening factor to each focus score based on the associated motion information with the dampening factor indicating how fast a filter reacts to changes in the focus scores.

22. The method of claim 21, further comprising:

performing an autofocus scan for a lens of the image capturing device; and

obtaining the plurality of focus scores associated with the autofocus scan, wherein motion information for the device is associated with each focus score.

23. The device of claim 21, wherein the one or more motion sensors comprise an accelerometer.

24. A method, comprising:

determining motion information for an image capturing device using a motion sensor;

determining whether the device is moving based on the motion information;

starting or stopping an autofocus mechanism based on the motion information; and

parking a lens position of a lens of the device at a hyperfocal position if the device is moving for a period of time that compares in a predetermined manner with a threshold value.