METHODS FOR BACKGROUND SUBTRACTION USING FOCUS DIFFERENCES

• US 20150093030A1
• Filed: 12/08/2014
• Published: 04/02/2015
• Est. Priority Date: 10/31/2012
• Status: Active Grant

• Current Assignee: West Texas Technology Partners LLC
• Original Assignee: Atheer, Inc.
• Inventors: Chehade, Mohamed Nabil Hajj, Fateh, Sina, Itani, Sleiman, Yang, Allen Yang
• Granted Patent: US 10,070,054 B2
• Time in Patent Office: Days
• US Class Current: 382/173
• CPC Class Codes: G06T 2207/10004 Still image; Photographic image
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 7/11 Region-based segmentation
• CPC Class Codes: G06T 7/174 involving the use of two or more images
• CPC Class Codes: G06T 7/194 involving foreground-background segmentation
• CPC Class Codes: G06T 7/557 from light fields, e.g. from plenoptic cameras
• CPC Class Codes: G06T 7/571 from focus
• CPC Class Codes: H04N 13/239 using two 2D image sensors having a relative position equal to or related to the interocular distance H04N13/243 takes precedence
• CPC Class Codes: H04N 23/45 for generating image signals from two or more image sensors being of different type or operating in different modes, e.g. with a CMOS sensor for moving images in combination with a charge-coupled device [CCD] for still images
• CPC Class Codes: H04N 23/80 Camera processing pipelines; Components thereof
• CPC Class Codes: H04N 23/959 by adjusting depth of field during image capture, e.g. maximising or setting range based on scene characteristics

Abstract

First and second images are captured at first and second focal lengths, the second focal length being longer than the first focal length. Element sets are defined with a first element of the first image and a corresponding second element of the second image. Element sets are identified as background if the second element thereof is more in-focus than or as in-focus as the first element. Background elements are subtracted from further analysis. Comparisons are based on relative focus, e.g. whether image elements are more or less in-focus. Measurement of absolute focus is not necessary, nor is measurement of absolute focus change; images need not be in-focus. More than two images, multiple element sets, and/or multiple categories and relative focus relationships also may be used.

Claims

1. A method, comprising steps of:

receiving a first image with a first focal length and a first field of view;

receiving a second image with a second focal length longer than said first focal length and a second field of view substantially identical to said first field of view;

defining a plurality of element sets, each said element set comprising a first element in said first image and a substantially corresponding second element in said second image;

comparing said first and second elements in said element sets, with regard to a relative focus thereof;

assigning as background any of said element sets wherein said second element thereof is more in-focus than or substantially equally in-focus as said first element therein; and

excluding said element sets assigned as background from further analysis.

2. The method of claim 1, wherein:

for a foreground object in said first and second images, neither said first image nor said second image is substantially fully in-focus.

3. The method of claim 1, wherein:

said first focal length is less than a distance to a foreground object in said field of view.

4. The method of claim 1, wherein:

said first focal length is substantially equal to a distance to a foreground object in said field of view.

5. The method of claim 1, wherein:

said first focal length is greater than a distance to a foreground object in said field of view.

6. The method of claim 1, wherein:

said second focal length is less than a distance to a foreground object in said field of view.

7. The method of claim 1, wherein:

said second focal length is substantially equal to a distance to a foreground object in said field of view.

8. The method of claim 1, wherein:

said second focal length is greater than a distance to a foreground object in said field of view.

9. The method of claim 1, wherein:

said first focal length is approximately at least an anticipated distance to a foreground object in said field of view.

10. The method of claim 1, wherein:

said first focal length corresponds to a length of a user'"'"'s arm.

11. The method of claim 2, wherein:

said first focal length images to a maximum extension of a user'"'"'s hand.

12. The method of claim 2, wherein:

said first focal length is at least 0.5 meters.

13. A method, comprising steps of:

receiving a plurality of images having unique focal lengths and substantially sharing a field of view;

determining a sequence of said images of increasing focal length, such that an n+1th image has a longer focal length than an nth image;

defining in said plurality of images at least one element set, each said element set comprising substantially corresponding elements in said plurality of images;

comparing said substantially corresponding elements in each said element set with regard to a relative focus thereof; and

identifying as a first category any of said element sets wherein said relative focus of said sequence of images satisfies a first relationship.

14. The method of claim 13, wherein:

for a foreground object in said images, none of said images is substantially fully in-focus.

15. The method of claim 13, wherein:

a shortest focal length of said plurality of images is less than a distance to a foreground object in said field of view.

16. The method of claim 13, wherein:

a shortest focal length of said plurality of images is substantially equal to a distance to a foreground object in said field of view.

17. The method of claim 13, wherein:

a shortest focal length of said plurality of images is greater than a distance to a foreground object in said field of view.

18. The method of claim 13, wherein:

a longest focal length of said plurality of images is less than a distance to a foreground object in said field of view.

19. The method of claim 13, wherein:

a longest focal length of said plurality of images is substantially equal to a distance to a foreground object in said field of view.

20. The method of claim 13, wherein:

a longest focal length of said plurality of images is greater than a distance to a foreground object in said field of view.

21. The method of claim 13, wherein:

a shortest focal length of said plurality of images is approximately at least an anticipated distance to a foreground object in said field of view.

22. The method of claim 13, wherein:

a shortest focal length of said plurality of images corresponds to a length of a user'"'"'s arm.

23. The method of claim 13, wherein:

a shortest focal length of said plurality of images corresponds to a maximum extension of a user'"'"'s hand.

24. The method of claim 13, wherein:

a shortest focal length of said plurality of images is at least 0.5 meters.

25. A method, comprising steps of:

receiving a plurality of images having unique focal lengths and substantially sharing a field of view, wherein for a foreground object in said images none of said images is substantially fully in-focus;

determining a sequence of said images of increasing focal length, such that an n+1th image has a longer focal length than an nth image;

defining in said plurality of images at least one element set, each said element set comprising substantially corresponding elements in said plurality of images;

comparing said substantially corresponding elements in each said element set with regard to a relative focus thereof;

assigning as background any of said element sets wherein said relative focus of said sequence of images satisfies a first relationship;

wherein;

a shortest focal length of said plurality of images is less than a distance to a foreground object in said field of view; and

a longest focal length of said plurality of images is greater than a distance to a foreground object in said field of view.