Smoke detection method and apparatus

• US 20050100193A1
• Filed: 11/08/2004
• Published: 05/12/2005
• Est. Priority Date: 11/07/2003
• Status: Active Grant

• Current Assignee: FIKE Video Analytics Corporation
• Original Assignee: axonX LLC
• Inventors: Privalov, George
• Granted Patent: US 7,805,002 B2
• Time in Patent Office: Days
• US Class Current: 382/103
• CPC Class Codes: G08B 17/103 using a light emitting and receiving device
• CPC Class Codes: G08B 17/107 for detecting light-scattering due to smoke
• CPC Class Codes: G08B 17/125 by using a video camera to detect fire or smoke

Abstract

A smoke detection method and system, which uses the effects of the diffusion of light to identify the presence of smoke in a monitored area, are disclosed. This method comprises the steps of: (1) electronically capturing a sequence of images of a light source in the monitored area, (2) transferring these images into an image buffer, (3) scanning these images to identify the chunks of adjacent pixels with brightness values above a prescribed threshold, (4) maintaining the sequence of such chunks obtained from consecutive images in a cluster stack, (5) analyzing the evolution of the features of each of these cluster over a prescribed period of time to identify the patterns that are caused by particle-induced light diffusion, and (6) issuing a prescribed system response in the event such light diffuised patterns are identified.

Claims

1. A method of detecting smoke in a monitored area containing a light source, said method comprising the steps of:

capturing, at a point in said monitored area that is distant from said light source and at a prescribed frequency, video images of said light source in the form of two-dimensional bitmaps,

wherein the spatial resolution of said bitmap is determined by the number of pixels comprising said bitmaps,

wherein the pixels corresponding to said light source are identified as such by the brightness levels of said pixels exceeding a prescribed threshold value, temporally monitoring the smoke influenced properties reflected in said bitmaps of the pixels corresponding to said light source so as to identify the presence of smoke in said monitored area,

wherein said smoke influenced properties of said pixels chosen from the group consisting of the size of the bitmap area associated with those pixels that are identified as corresponding to said light source, the variations in the brightness of said pixels that are identified as corresponding to said light source, and the shape of the bitmap area associated with those pixels that are identified as corresponding to said light source.

2. The method of smoke detection as recited in claim 1, wherein said brightness level threshold is dynamically adjusted for temporal changes in the background brightness conditions within said monitored area.

3. The method of smoke detection as recited in claim 1, wherein:

the calculation of the temporal change in the size of the bitmap area, that is associated with those pixels that are identified as corresponding to said light source, is approximated by an assumed linear trend in said size change over a prescribed period of time, and

the magnitude of the rate of this assumed linear trend being above a prescribed value is used to identify the presence of smoke in said monitored area.

4. The method of smoke detection as recited in claim 1, wherein:

the calculation of the temporal change in the variation in the brightness levels of said pixels that are identified as corresponding to said light source utilizes the computation of the Shannon entropy for said pixels, and

the increase over time of said Shannon entropy being above a prescribed value is used to identify the presence of smoke in said monitored area.

5. The method of smoke detection as recited in claim 1, wherein:

the calculation of the temporal change in the variation in the brightness levels of said pixels that are identified as corresponding to said light source utilizes the computation of the changes in the shape of the histograms of the brightness levels corresponding to said successive captured images.

6. The method of smoke detection as recited in claim 1, further comprising the step of:

in the event that said presence of smoke in said monitored area is identified, signaling the detection of smoke in said monitored area.

7. An apparatus for detecting smoke in a monitored area having a light source, said apparatus comprising:

a means, located at a point in said monitored area that is distant from said light source, for capturing at a prescribed frequency, video images of said light source in the form of two-dimensional bitmaps having a specified number of pixels,

a means for cyclically accumulating a sequential set of said captured bitmaps,

a means for examining said set of bitmaps to identify those pixels in said bitmaps that correspond to said light source, said identification being dependent upon the brightness levels of said pixels exceeding a prescribed threshold value,

a means for temporally monitoring and analyzing the smoke influenced properties reflected in said bitmaps of the pixels corresponding to said light source so as to identify the presence of smoke in said monitored area,

wherein said smoke influenced properties of said pixels chosen from the group consisting of the size of the bitmap area associated with those pixels that are identified as corresponding to said light source, the variations in the brightness of said pixels that are identified as corresponding to said light source, and the shape of the bitmap area associated with those pixels that are identified as corresponding to said light source.

8. The apparatus as recited in claim 7, wherein said brightness level threshold is dynamically adjusted for temporal changes in the background brightness conditions within said monitored area.

9. The apparatus as recited in claim 7, wherein:

the calculation of the temporal change in the size of the bitmap area, that is associated with those pixels that are identified as corresponding to said light source, is approximated by an assumed linear trend in said size change over a prescribed period of time, and

the magnitude of the rate of this assumed linear trend being above a prescribed value is used to identify the presence of smoke in said monitored area.

10. The apparatus as recited in claim 7, wherein:

the calculation of the temporal change in the variation in the brightness levels of said pixels that are identified as corresponding to said light source utilizes the computation of the Shannon entropy for said pixels, and

the increase over time of said Shannon entropy being above a prescribed value is used to identify the presence of smoke in said monitored area.

11. The apparatus as recited in claim 7, wherein:

the calculation of the temporal change in the variation in the brightness levels of said pixels that are identified as corresponding to said light source utilizes the computation of the changes in the shape of the histograms of the brightness levels corresponding to said successive captured images.

12. The apparatus as recited in claim 7, fuirther comprising:

a means for, in the event that said presence of smoke in said monitored area is identified, signaling the detection of smoke in said monitored area.