Search range extension for depth assisted autofocus

Patent metadata

Field	Value
Publication number	US-9638984-B2
Application number	US-201514825964-A
Country	US
Kind code	B2
Filing date	Aug 13, 2015
Priority date	Mar 10, 2015
Publication date	May 2, 2017
Grant date	May 2, 2017

Abstract

Systems and methods described herein can adjust a search range generated by a camera using depth-assisted autofocus based in part on measuring focus values in a first search range. For example, in some embodiments, a method includes estimating a depth of an object to be captured in an image, determining a first range of lens positions based at least in part on the estimating, moving the lens of the camera to a plurality of lens positions within the first range of lens positions, capturing a plurality of images, the plurality of images being captured at one or more of the plurality of lens positions, generating one or more focus values based on the plurality of images, and determining one or more additional lens positions or a second range of lens positions based at least in part on the one or more focus values.

First claim

What is claimed is:

1. A method for autofocus in an imaging device, the method comprising:
receiving depth information of an object within a scene;
determining, for an autofocus lens system, a first lens position and a second lens position defining outer boundaries of a first range including a first plurality of lens positions based on the depth information;
for each lens position of the first plurality of lens positions:
setting a lens of the autofocus lens system to the lens position; and
generating a focus value associated with the lens position;

generating, based on the focus values associated with each of the first plurality of lens positions, data representing a focus value curve;
identifying a slope of the focus value curve at each of the first plurality of lens positions;
determining, based at least partly on the slope of the focus value curve at each of the first plurality of lens positions, whether a maximum focus value is within the first range;
in response to determining that the maximum focus value is not within the first range:
determining that the slope of the focus value curve is increasing at one of the first lens position and the second lens position;
determining a second range including a second plurality of lens positions, the second range bounded by the one of the first lens position and the second lens position and a third lens position outside of the first range;
setting the lens to the second plurality of lens positions in the second range;
determining whether the maximum focus value is within the second range of lens positions; and
in response to determining that the maximum focus value is within the second range, capturing an image by the imaging device with the lens at a position in the second range corresponding to the maximum focus value.

2. The method of claim 1 , wherein the focus value indicates a measure of how well an image is focused, a higher focus value indicating a more well focused image.

3. The method of claim 1 , further comprising determining a focus value at each of the second plurality of lens positions in the second range.

4. The method of claim 1 , wherein each lens position corresponds to a focusing distance for the autofocus lens system, the focusing distance at the first lens position in the first range less than the focusing distance at the second lens position in the first range, and wherein the second plurality of lens positions in the second range are determined such that,
the second plurality of lens positions in the second range have focusing distances less than the focusing distance at the first lens position when the slope of the focus value curve is increasing at the first lens position, and
the second plurality of lens positions in the second range have focusing distances greater than the focusing distance at the second lens position when the slope of the focus value curve is increasing at the second lens position.

5. The method of claim 1 , wherein the focus value indicates sharpness or contrast of an image captured with the lens at a set lens position.

6. The method of claim 1 , wherein said setting the lens comprises moving the lens by an open-loop VCM actuator.

7. The method of claim 1 , wherein the first plurality of lens positions in the first range are separated by a uniform step size, the step size corresponding to one or more intermediate lens positions between the first and second lens positions in the first range.

8. The method of claim 1 , further comprising determining an order to set the lens to second plurality of lens positions in the second range that minimizes a total time to set the lens to each lens position.

9. The method of claim 1 , wherein the depth information represents a distance of the object in the scene from the imaging device, the method further comprising:
determining a first intermediate lens position corresponding to a focusing distance corresponding to the distance of the object from the imaging device; and
determining the first lens position and second lens position based on a tolerance on each side of the first intermediate lens position.

10. A non-transitory computer readable storage medium storing instructions that, when executed, cause at least one physical computer processor of an imaging device to perform a method comprising:
receiving depth information of an object within a scene;
determining, for an autofocus lens system, a first lens position and a second lens position defining outer boundaries of a first range including a first plurality of lens positions based on the depth information;
for each lens position of the first plurality of lens positions:
setting a lens of the autofocus lens system to the lens position; and
generating a focus value associated with the lens position;

generating, based on the focus values associated with each of the first plurality of lens positions, data representing a focus value curve;
identifying a slope of the focus value curve at each of the first plurality of lens positions;
determining, based at least partly on the slope of the focus value curve at each of the first plurality of lens positions, whether a maximum focus value is within the first range;
in response to determining that the maximum focus value is not within the first range:
determining that the slope of the focus value curve is increasing at one of the first lens position and the second lens position;
determining a second range including a second plurality of lens positions, the second range bounded by the one of the first lens position and the second lens position and a third lens position outside of the first range;
setting the lens to the second plurality of lens positions in the second range;
determining whether the maximum focus value is within the second range of lens positions; and
in response to determining that the maximum focus value is within the second range, capturing an image by the imaging device with the lens at a lens position in the second range corresponding to the maximum focus value.

11. The non-transitory computer readable storage medium of claim 10 , wherein the method further comprises determining a focus value at each of the lens positions in the second range of lens positions.

12. The non-transitory computer readable storage medium of claim 10 , wherein each lens position corresponds to a focusing distance for the autofocus lens system, the focusing distance at the first lens position in the first range less than the focusing distance at the second lens position in the first range, and wherein the second plurality of lens positions in the second range are determined such that,
the second plurality of lens positions in the second range have focusing distances less than the focusing distance at the first lens position when the slope of the focus value curve is increasing at the first lens position, and
the second plurality of lens positions in the second range have focusing distances greater than the focusing distance at the second lens position when the slope of the focus value curve is increasing at the second lens position.

13. The non-transitory computer readable storage medium of claim 10 , wherein depth information represents a distance of an object in the scene from the imaging device, and wherein the method further comprises:
determining a first intermediate lens position corresponding to a focusing distance corresponding to the distance of the object from the imaging device; and
determining the first lens position and second lens position based on a tolerance on each side of the first intermediate lens position.

14. An apparatus, comprising:
an autofocus l

Assignees

• Qualcomm Inc

Inventors

• Lou Ying Chen
• Krishnamurthy Sagar Sanket
• Velarde Ruben Manuel

Classifications

• H04N23/673

  based on contrast or high frequency components of image signals, e.g. hill climbing method · CPC title

• H04N23/676

  Bracketing for image capture at varying focusing conditions · CPC title

• G02B7/285 Primary

  including two or more different focus detection devices, e.g. both an active and a passive focus detecting device · CPC title

• H04N5/2226

  Determination of depth image, e.g. for foreground/background separation (determining depth by image analysis in general G06T7/50; segmentation by image analysis in general G06T7/10) · CPC title

• G03B13/36

  Autofocus systems · CPC title