Fire detection method and apparatus

• US 20050271247A1
• Filed: 05/17/2005
• Published: 12/08/2005
• Est. Priority Date: 05/18/2004
• Status: Active Grant

• Current Assignee: Axonx Fike Corporation
• Original Assignee: axonX LLC
• Inventors: Privalov, George
• Granted Patent: US 7,680,297 B2
• Time in Patent Office: Days
• US Class Current: 382/100
• CPC Class Codes: G06V 20/40 in video content extracting overlay text G06V20/62; video retrieval G06F16/70; processing of video elementary streams in video servers H04N21/234; processing of video elementary streams in video clients H04N21/44

Abstract

The present invention provides a method and apparatus for detecting fire in a monitored area even if the flames are hidden behind obstructing objects. The steps of this method include: (a) detecting and capturing, at a prescribed frequency, video images of the monitored area, (b) converting the captured images into two-dimensional bitmaps of the temporally varying brightness values observed in the captured images, wherein the spatial resolution of this bitmap is determined by the number of pixels comprising the bitmaps, (c) specifying for any two of the pixels in the bitmaps a temporal coherence factor whose magnitude is a measure over a prescribed time of the similarities observed in the temporal variations of the brightness values being captured at each of the bitmap'"'"'s pixels, (d) computing this temporal coherence factors for each of the prescribed set of pixels in the captured images, and (e) analyzing the computed temporal coherence factors to identify those sets of pixels that have temporal coherence factors whose values are above a prescribed threshold value, wherein this prescribed threshold value is set so as to identify those pixels that correspond to regions of the monitored area whose temporal variations in brightness indicate that the source of this brightness is a fire in the monitored area.

Claims

1. A method of fire detection in a monitored area comprising the steps of:

detecting and capturing, at a prescribed frequency, video images of said area,

converting said captured images into two-dimensional bitmaps of the temporally varying brightness values observed in said images, wherein the spatial resolution of said bitmap being determined by the number of pixels comprising said bitmaps,

specifying for any two of said pixels in said bitmaps a temporal coherence factor whose magnitude is a measure over a prescribed time of the similarities observed in the temporal variations of the brightness values being captured at each of said pixels,

computing said temporal coherence factors for each of said prescribed set of pixels in said captured images, and

analyzing said computed temporal coherence factors to identify those sets of pixels that have temporal coherence factors whose values are above a prescribed threshold value,

wherein said prescribed threshold value set so as to identify those pixels that correspond to regions of said monitored area whose temporal variations in brightness indicate that the source of said brightness is a fire in said monitored area.

2. A method of fire detection as recited in claim 1, wherein said sets of pixels are pairs of adjacent pixels along the horizontal and vertical axes defining said bitmap.

3. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any two arbitrary pixels in said bitmaps is the convolution of the time derivative of the brightness values of said pixels.

4. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum across a prescribed number of samples of products of brightness differences of said pixels in successive bitmaps.

5. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any arbitrary pair of pixels is the timed-averaged sum of products of the brightness differences of said pixels in successive bitmaps.

6. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any two arbitrary pixels is the sum across a prescribed number of samples of the products of differences in current brightness value and the time-averaged brightness value of said pixels.

7. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any arbitrary pair of pixels is the time-averaged sum of products of differences in current brightness value and the time-averaged brightness value of the said pixels.

8. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum of the products of the Fourier terms of the time derivative brightness of one pixel and the complex conjugate Fourier terms of another pixel.

9. A method of fire detection as recited in claim 1, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum of the products of non-zero Fourier terms of brightness value of one pixel and the complex conjugate Fourier terms of brightness value of another pixel performed over a prescribed range of terms.

10. A method of fire detection as recited in claim 1, further comprising the step of issuing an alarm that signifies when said area associated with said pixels having said temporal coherence factors above said threshold value has exceed a prescribed size.

11. An apparatus for fire detection within a monitored area, said apparatus comprising:

a means for detecting and capturing, at a prescribed frequency, video images of said area,

a means for converting said captured images into two-dimensional bitmaps of the temporally varying brightness values observed in said images, wherein the spatial resolution of said bitmap being determined by the number of pixels comprising said bitmaps,

a means for specifying for any two of said pixels in said bitmaps a temporal coherence factor whose magnitude is a measure over a prescribed time of the similarities observed in the temporal variations of the brightness values being captured at each of said pixels,

a means for computing said temporal coherence factors for each of said prescribed set of pixels in said captured images, and

a means for analyzing said computed temporal coherence factors to identify those sets of pixels that have temporal coherence factors whose values are above a prescribed threshold value,

wherein said prescribed threshold value set so as to identify those pixels that correspond to regions of said monitored area whose temporal variations in brightness indicate that the source of said brightness is a fire in said monitored area.

12. An apparatus for fire detection as recited in claim 11, wherein said sets of pixels are pairs of adjacent pixels along the horizontal and vertical axes defining said bitmap.

13. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any two arbitrary pixels in said bitmaps is the convolution of the time derivative of the brightness values of said pixels.

14. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum across a prescribed number of samples of products of brightness differences of said pixels in successive bitmaps.

15. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any arbitrary pair of pixels is the timed-averaged sum of products of the brightness differences of said pixels in successive bitmaps.

16. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any two arbitrary pixels is the sum across a prescribed number of samples of the products of differences in current brightness value and the time-averaged brightness value of said pixels.

17. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any arbitrary pair of pixels is the time-averaged sum of products of differences in current brightness value and the time-averaged brightness value of the said pixels.

18. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum of the products of the Fourier terms of the time derivative brightness of one pixel and the complex conjugate Fourier terms of another pixel.

19. An apparatus for fire detection as recited in claim 11, wherein said temporal coherence factor of any arbitrary pair of pixels is the sum of the products of non-zero Fourier terms of brightness value of one pixel and the complex conjugate Fourier terms of brightness value of another pixel performed over a prescribed range of terms.

20. An apparatus for fire detection as recited in claim 11, further comprising a means for issuing an alarm that signifies when said area associated with said pixels having said temporal coherence factors above said threshold value has exceed a prescribed size.