Method of tracking an object in a video stream

• US 20070097112A1
• Filed: 07/21/2006
• Published: 05/03/2007
• Est. Priority Date: 10/31/2005
• Status: Active Grant

• Current Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Original Assignee: Hewlett-Packard Development Company, L.P. (HP Inc.)
• Inventors: Greig, Darryl
• Granted Patent: US 8,224,023 B2
• Time in Patent Office: Days
• US Class Current: 345/419
• CPC Class Codes: G01C 11/04 Interpretation of pictures
• CPC Class Codes: G06T 7/238 using non-full search, e.g. three-step search

Abstract

A method of tracking an object such as a face in a video stream comprises running an object detector at a plurality of locations on a first frame, defining a coarse grid. This is repeated for second and subsequent frames, with the grid slightly offset each time so that, ultimately, all of the points on a fine grid are covered but in several passes. When an object such as a face is located on one frame, positional and/or scale information is propagated to the next frame to assist in the tracking of that object onto the next frame.

Claims

1. A method of tracking an object in a video stream comprising a plurality of video frames, the method comprising:

(a) running an object detector at a plurality of sampling locations, the locations defining a first grid spaced across a first frame, and recording a hit at each location where an object of interest is found; and

(b) running the object detector at a further plurality of sampling locations defining a second grid spaced across a second frame, the second grid being offset from the first grid, and running the detector in addition at one or more further locations on the second frame derived from the or each location on the first frame at which a hit was recorded.

2. A method of tracking an object in a video stream as claimed in claim 1 in which the said further locations on the second frame are the same as the locations on the first frame at which a hit was recorded.

3. A method claimed as in claim 1 in which the said further locations on the second frame are derived by carrying out a neighbourhood search around the locations on the first frame at which a hit was recorded.

4. A method claimed as in claim 1 in which the said further locations are derived by predicting the movement of the or each object located on the first frame to one or more estimated locations in the second frame, the estimated locations being selected as the said further locations.

5. A method claimed as in claim 1 in which the said further locations are derived by predicting the movement of the or each object located on the first frame to one or more estimated location in the second frame, the further locations being chosen by carrying out a neighbourhood search around the said estimated locations.

6. A method as claimed in claim 1 including repeating step (b) for a sequence of subsequent frames, each respective sampling grid being offset from the grid used on the preceding frame.

7. A method as claimed in claim 1 in which each time the object detector runs it attempts to find an object of interest at a plurality of different scales.

8. A method as claimed in claim 1 for operating on a real-time video stream, and in which the object detector operates in sub-real-time.

9. A method as claimed in claim 1 in which the object detector is a face detector.

10. Apparatus for tracking an object in a video stream comprising a plurality of video frames, the apparatus including an object detector comprising a programmed computer for:

(a) running an object detector at a plurality of sampling locations, the locations defining a first grid spaced across a first frame, and recording a hit at each location where an object of interest is found; and

(b) running the object detector at a further plurality of sampling locations defining a second grid spaced across a second frame, the second grid being offset from the first grid, and running the detector in addition at one or more further locations on the second frame derived from the or each location on the first frame at which a hit was recorded.

11. Apparatus as claimed in claim 10 in which the said further locations on the second frame are the same as the locations on the first frame at which a hit was recorded.

12. Apparatus as claimed in claim 10 in which the said further locations on the second frame are derived by carrying out a neighbourhood search around the locations on the first frame at which a hit was recorded

13. Apparatus as claimed in claim 10 in which the said further locations are derived by predicting the movement of the or each object located on the first frame to one or more estimated locations in the second frame, the estimated locations being selected as the said further locations.

14. Apparatus as claimed in claim 10 in which the said further locations are derived by predicting the movement of the or each object located on the first frame to one or more estimated location in the second frame, the further locations being chosen by carrying out a neighbourhood search around the said estimated locations.

15. Apparatus as claimed in claim 10 including repeating (b) for a sequence of subsequent frames, each respective sampling grid being offset from the grid used on the preceding frame.

16. Apparatus as claimed in claim 10 in which each time the object detector runs it attempts to find an object of interest at a plurality of different scales.

17. Apparatus as claimed in claim 10 for operating on a real-time video stream, and in which the object detector operates in sub-real-time.

18. Apparatus as claimed in claim 10 in which the object detector is a face detector.

19. A camera including apparatus as claimed in claim 10.