IDENTIFYING STALE BACKGROUND PIXELS IN A VIDEO ANALYSIS SYSTEM

• US 20090087086A1
• Filed: 05/29/2008
• Published: 04/02/2009
• Est. Priority Date: 09/27/2007
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Behavioral Recognition Systems Incorporated
• Inventors: Cobb, Wesley Kenneth, Saitwal, Kishor Adinath, Blythe, Bobby Ernest, Eaton, John Eric
• Granted Patent: US 8,041,116 B2
• Time in Patent Office: Days
• US Class Current: 382/164
• CPC Class Codes: G06V 10/28 Quantising the image, e.g. histogram thresholding for discrimination between background and foreground patterns

Abstract

Embodiments of the present invention provide a method and a module for identifying a background of a scene depicted in an acquired stream of video frames that may be used by a video-analysis system. For each pixel or block of pixels in an acquired video frame a comparison measure is determined. The comparison measure depends on difference of color values exhibited in the acquired video frame and in a background image respectively by the pixel or block of pixels and a corresponding pixel and block of pixels in the background image. To determine the comparison measure, the resulting difference is considered in relation to a range of possible color values. If the comparison measure is above a dynamically adjusted threshold, the pixel or the block of pixels is classified as a part of the background of the scene.

Claims

1. A method for identifying stale background pixels in a background model of scene depicted in a sequence of video frames, the method comprising:

receiving a raw video frame of the sequence of video frames;

classifying a first set of one or more pixels of the raw video frame as depicting a portion of a background of the scene;

classifying a second set of one or more pixels of the raw video frame as depicting a portion of a foreground of the scene;

for at least a first pixel classified as depicting a portion of the foreground of the scene;

selecting a background pixel in the background model corresponding to the first pixel and a plurality of pixels in the background model neighboring the background pixel,

determining a plurality of changes between color-characteristic values of the plurality of pixels in the background model and respective color-characteristic values of a corresponding plurality of pixels in a video frame previously used to update the color-characteristic values of the background pixel, and

upon determining a difference between the change and the plurality of changes is within a specified threshold, classifying the background pixel in the background model as a stale background pixel; and

updating the color-characteristic values of the background pixel in the background model using the color-characteristic values of the first pixel.

2. The method of claim 1, further comprising, upon determining the plurality of changes is within the specified threshold, re-classifying the first pixel as depicting a portion of a background of the scene.

3. The method of claim 1, wherein color-characteristics are selected from a group consisting of a Red (R) color-channel, a Green (G) color-channel, and a Blue (B) color-channel.

4. The method of claim 1, wherein the background model includes a background image composed from a plurality of pixel color values, and wherein the background images depicts static elements of the scene depicted in the sequence of video frames.

5. The method of claim 1, wherein the operation further comprises updating the background model using the first set of one or more pixels.

6. The method of claim 1, wherein the background model includes a short-term background model and a long-term background model.

8. The computer-readable storage medium of claim 6, wherein the operation further comprises, upon determining the plurality of changes is within the specified threshold, re-classifying the first pixel as depicting a portion of a background of the scene.

9. The computer-readable storage medium of claim 6, wherein color-characteristics are selected from a group consisting of a Red (R) color-channel, a Green (G) color-channel, and a Blue (B) color-channel.

10. The computer-readable storage medium of claim 6, wherein the background model includes a background image composed from a plurality of pixel color values, and wherein the background images depicts static elements of the scene depicted in the sequence of video frames.

11. The computer-readable storage medium of claim 6, wherein the operation further comprises updating the background model using the first set of one or more pixels.

12. The computer-readable storage medium of claim 6, wherein the background model includes a short-term background model and a long-term background model.

7. A computer-readable storage medium containing a program which, when executed by a processor, performs an operation for identifying stale background pixels in a background model of scene depicted in a sequence of video frames, the operation comprising:

receiving a raw video frame of the sequence of video frames;

classifying a first set of one or more pixels of the raw video frame as depicting a portion of a background of the scene;

classifying a second set of one or more pixels of the raw video frame as depicting a portion of a foreground of the scene;

for at least a first pixel classified as depicting a portion of the foreground of the scene;

selecting a background pixel in the background model corresponding to the first pixel and a plurality of pixels in the background model neighboring the background pixel,

determining a plurality of changes between color-characteristic values of the plurality of pixels in the background model and respective color-characteristic values of a corresponding plurality of pixels in a video frame previously used to update the color-characteristic values of the background pixel, and

upon determining a difference between the change and the plurality of changes is within a specified threshold, classifying the background pixel in the background model as a stale background pixel; and

updating the color-characteristic values of the background pixel in the background model using the color-characteristic values of the first pixel.

13. A system, comprising:

a video input source configured to provide a sequence of video frames, each depicting a scene;

a processor; and

a memory containing a video analysis application, which when executed by the processor is configured to perform an operation for identifying stale background pixels in a background model of scene depicted in a sequence of video frames, the operation comprising;

receiving a raw video frame of the sequence of video frames,

classifying a first set of one or more pixels of the raw video frame as depicting a portion of a background of the scene,

classifying a second set of one or more pixels of the raw video frame as depicting a portion of a foreground of the scene, and

for at least a first pixel classified as depicting a portion of the foreground of the scene;

selecting a background pixel in the background model corresponding to the first pixel and a plurality of pixels in the background model neighboring the background pixel,

determining a plurality of changes between color-characteristic values of the plurality of pixels in the background model and respective color-characteristic values of a corresponding plurality of pixels in a video frame previously used to update the color-characteristic values of the background pixel, and

upon determining a difference between the change and the plurality of changes is within a specified threshold, classifying the background pixel in the background model as a stale background pixel; and

updating the color-characteristic values of the background pixel in the background model using the color-characteristic values of the first pixel.

14. The system of claim 13, further comprising, upon determining the plurality of changes is within the specified threshold, re-classifying the first pixel as depicting a portion of a background of the scene.

15. The system of claim 13, wherein color-characteristics are selected from a group consisting of a Red (R) color-channel, a Green (G) color-channel, and a Blue (B) color-channel.

16. The system of claim 13, wherein the background model includes a background image composed from a plurality of pixel color values, and wherein the background images depicts static elements of the scene depicted in the sequence of video frames.

17. The system of claim 13, wherein the operation further comprises updating the background model using the first set of one or more pixels.

18. The system of claim 13, wherein the background model includes a short-term background model and a long-term background model.