AU2004202851B2

AU2004202851B2 - Method and Device for Detecting Flames

Info

Publication number: AU2004202851B2
Application number: AU2004202851A
Authority: AU
Inventors: Giuseppe Marbach
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2003-07-11
Filing date: 2004-06-25
Publication date: 2008-08-28
Anticipated expiration: 2024-06-25
Also published as: NO330182B1; DE50306852D1; KR20050009135A; CN100595583C; NO20042948L; ES2282550T3; AU2004202851A1; NO20042948D0; EP1496483A1; PL369016A1; ATE357714T1; EP1496483B1; CN1576839A

Abstract

A flame detection procedure (2) analyses a video (1) image (3) for bright spots and moving areas using a weighted accumulation matrix (4) constructed from the differences between successive images with low intensity and so dark moving objects filtered (5) out to leave small areas of interest for integration (6) and flame presence probability (7) estimation (8). Includes INDEPENDENT CLAIMs for equipment using the procedure.

Description

S&F Ref: 681004

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Siemens Building Technologies AG, of Bellerivestrasse 36, 8008, Zirich, Switzerland Giuseppe Marbach Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Method and Device for Detecting Flames The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c 24/01 2008 THU 14:58 FAX Smoorenburg Attorneys IP AUSTRALIA R005/021 00 2 c- Method and device for detecting flames SDescription SField of the invention C In particular arrangements, the present invention relates to a method and a device for detecting flames in a monitored zone, referred to hereinafter as Imonitoring space, by analysis of at least one parameter of a radiation that occurs

V)

00 in the monitoring space.

c,-i Background to the Invention Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.

Previous devices, as are described for example in US Patents No.

4,866,420 and No. 4,280,058, contain at least one sensor which evaluates the flicker frequency spectrum of the radiation, signals lying outside a specific frequency band being assessed as interference signals. The typical flicker of the flames in a very low-frequency oscillation range is thus used as a feature for distinguishing between the radiation emitted by a flame and interference radiation. In the simplest case, the frequency band is defined by filters connected upstream of the sensor, or by frequency-selective amplifiers connected downstream thereof, a specific passband of 5 to 25 Hz, for example, being obtained in both cases.

These flames detectors have proved to be successful, but they represent a not inconsiderable cost factor in a fire alarm system. Apart from that, even with optimum tuning of the frequency band to the flicker of flames, disturbances and incorrect indications cannot be precluded because it happens again and again that random changes in intensity of the ambient radiation lie in the passband.

Such changes in intensity may be caused for example by shading or reflections of vibrating or slowly moving objects, by reflections of sunlight on water surfaces or by flickering or fluctuating light sources.

COMS ID No: ARCS-176621 Received by IP Australia: Time 15:05 Date 2008-01-24 24/01 2008 THU 14:58 FAX Smoorenburg Attorneys IP AUSTRALIA Q006/021 00 3 O3 m It would be advantageous if there could be provided a method for detecting flames which is distinguished by high interference immunity in conjunction with low costs.

C Summary of the Invention According to a first aspect of arrangements herein described there is provided

V)

o00 a method for detecting flames in a monitoring space, by analysis of at least Sone parameter of a radiation that occurs in the monitoring space, said method comprising: generating a video image of the monitoring space, searching for zones having high light intensity and local flicker motion in said video image, the search for zones having high light intensity and local flicker motion being effected with the aid of an accumulation matrix, which is obtained from the difference images of successive intensity images, said differences being weighted with a weighting factor, the weighting factor specifying the extent to which the difference images influence the accumulation matrix, and said zones being localized and the relevant image excerpts being analyzed with regard to the present of a flame.

According to a second aspect of arrangements herein described there is provided a device for detecting flames in a monitoring space, by analysis of at least one parameter of a radiation that occurs in the monitoring space, said device comprising a video camera, an evaluation stage for the images supplied by the camera, the evaluation stage having a processor with an algorithm for the localization of regions having high light intensity and local flicker motion in the images of the camera and the subsequent analysis of the corresponding image excerpts with regard to the presence of a flame.

Advantageously in preferred embodiments there is provided a method characterized in that a video image of the monitoring space is generated and zones having high light intensity and local flicker motion are sought in said video image, in which case, in a first step, said zones are localized and the relevant COMS ID No: ARCS-176621 Received by IP Australia: Time 15:05 Date 2008-01-24 24/01 2008 THU 14:59 FAX Smoorenburg Attorneys IP AUSTRALIA I007/021 00 3a C1 image excerpts are subsequently analyzed with regard to the presence of a Sflame.

A first preferred embodiment of the method according to the invention is c characterized in that the video images are generated with a specific frequency and intensity images are attained therefrom.

A second preferred embodiment of the method according to the invention 00oO is characterized in that the search for zones having high light intensity and local flicker motion is effected with the aid of an accumulation matrix, which is obtained from the difference images of successive intensity images, said difference images being weighted with a weighting factor, the weighting factor specifying the extent to which the difference images influence the accumulation matrix.

A third preferred embodiment of the method according to the invention is characterized in that the coordinates of the brightest pixels are sought with the aid of the accumulation matrix.

A fourth preferred embodiment is characterized in that an image region of interest which contains the brightness pixel or pixels and is reduced with respect to the original image is defined and analyzed with regard to the presence of a flame.

Advantageously there is preferably provided a video camera with an evaluation stage for the images supplied by the camera, the evaluation stage having a processor with an algorithm for the localization of regions having high light intensity and local flicker motion in the images of the camera and the subsequent analysis of the corresponding image excerpts with regard to the presence of a flame.

As CCTV systems and installations are becoming ever more widespread, it can be assumed that in many cases a video camera will be present in a monitoring space, and so a dedicated sensor does not have to be installed for the flame detection, which undoubtedly means a reduction of costs. A further reduction of costs results from restricting the evaluation to the image excerpts possibly containing a flame, which enables the computer power to be significantly reduced. It can also be assumed that the evaluation of these image excerpts is sufficiently robust toward disturbances.

COMS ID No: ARCS-176621 Received by IP Australia: Time 15:05 Date 2008-01-24 24/01 2008 THU 14:59 FAX Smoorenburg Attorneys IP AUSTRALIA 008/021 00 3b 0 Further preferred embodiments of the method according to the invention emerge from each of the claims forming part of the present disclosure.

C Preferred arrangements of the present invention are described in more detail below by way of example with reference to a block diagram showing a device for detecting flames. The reference symbol 1 designates a video camera, 00 which, via an output, supplies video sequences to an evaluation stage 2, in which O the evaluation stage 2 may be integrated into the camera 1 or be connected thereto. The evaluation stage 2 may be provided at the location where the camera 1 is installed, or in direct proximity thereto, or it may also be provided spatially COMS ID No: ARCS-176621 Received by IP Australia: Time 15:05 Date 2008-01-24 4 remote from the camera 1, there being a communication link between camera 1 and evaluation stage 2 in the latter case.

The evaluation stage 2 contains a processor (not illustrated) having an algorithm for the localization of flames found in the images of the camera 1 and the subsequent analysis of the corresponding image excerpts. In accordance with the illustration, in a first process of the algorithm, designated image obtaining, intensity and/or chrominance images Xij (t) (referred to hereinafter as intensity images) are obtained from the video sequences supplied by the camera 1; i and j are the coordinates of the individual pixels. The frequency of these images is at least images per second, and the image size is 352 by 288 pixels, for example. Intensity images are obtained because it can be assumed that a flame represents a location having a high light intensity and additionally has a characteristic hue.

In a next process, designated preprocessing 4, flames are sought in the intensity images Xij(t) and the flames found are localized in corresponding image excerpts.

This localization is effected with the aid of a socalled accumulation matrix, which is formed in the following manner: In a first step the maximum value max [Xij(t)] and the mean value mean [Xij(t)] of the intensity are determined and a brightness threshold q(t) is determined therefrom, the following holding true: q(t+l) )i max [Xij if mean [Xij X, max [Xij and q(t+l) X 2 {max [Xij(t)] mean mean in all other cases.

X

1 and k 2 are constants lying between 0 and 1, in which case, by way of example, X, is equal to 0.68 and 2 is 5 equal to 0.05.

A weighting factor wij that takes account of the flame properties is determined with the aid of these two conditions: wj Xij(t) if Xij(t) max [Xij and wij(t) 0 in all other cases.

This means that all pixels having an intensity below the value max [Xij(t)] that is to say dark objects, are filtered out and not taken into account any further. As will directly be revealed, the objects filtered out are dark moving objects.

Since it can be assumed that a flame can be identified as motion having high light intensity, a difference image is formed by comparison of successive images in order to find such motion; since dark objects are omitted on account of the definition of the weighting factor wij(t), moving dark objects, which cannot be flames, are thus filtered out during the formation of the difference image. Zones having high light intensity and local flicker motion are thus sought and this means that, by way of example, a stationary light source which does not flicker would not be interpreted as a flame, and nor would a lamp moved transversely through the monitoring space.

The following hold trues for the difference image Qij i Xi t 4-ij. t-l 'I The difference image Qij(t) is then used to determine the accumulation matrix Aij(t): Aij(t) a Aij(t-1) Qij(t) a is a constant between 0 and 1 specifying the extent to which the difference image Qij(t) influences the 6 accumulation matrix Aij(t). For a 0, the accumulation matrix becomes equal to the difference image, and for a 1, the difference image no longer has an influence because Aij is equal to Aij(t-l). The accumulation matrix is primarily formed in order to obtain a smoothed image without noise and momentary changes.

As a final step of preprocessing 4, the pixel or pixels [im, jm[(t) having the highest value is or are sought with the aid of the accumulation matrix and a so-called image region of interest ROI which contains said pixel or pixels and in which a flame might be situated is defined: max [Aij(t)]} This determination thus supplies the coordinates of the pixels having local flicker motion and maximum brightness. Generally, a single pixel will be involved, but it is also possible, of course, to determine a plurality of brightest pixels, for which purpose a multichannel selection may be used and minimum spacings between the individual pixels are preferably defined.

In the next process, designated analysis 5, firstly a significant reduction of the data is effected in that the analysis is not effected in the entire original image of 352 by 288 pixels, but rather in the image region of interest ROI having a reduced size of 32 by 32 pixels, for example. This results in a reduction to a hundredth. This reduction may, of course, also be lower, for example to a fiftieth, or else significantly greater The following image information items are then determined for each image region of interest: Mean brightness L(t) of the image region of interest XRoi(t): L(t) [mean of Xij(t) IROI] Chrominance C(t) of the image region of interest 7 XROI C(t) [number of Cij(t) IRo] c "fire chroma sector" where Cij designates the chrominance pair (Vij, Uij) of the image Xij(t) at the time t. YUV is a known representation of the color space, with two color components U and V on the x and y axis, respectively, and the intensity Y on the z axis, the length of the vector from the zero point to a pixel in the UV plane specifies the color saturation of this pixel. The fire chroma sector R(t) is a sector of the color space in the UV plane, in the color range typical of a flame, which, in particular, contains the color red.

Number of active pixels R(t) of the accumulation matrix AROI(t) R(t) [Number of Aij(t) IRoI 1i]; 1 ri Z (Z total number of pixels of the image region of interest ROI) for example ri Degree of saturation S(t) of the image region of interest XRO S(t) [number of Xij(t) IROI T1 2 1 2 Z for example 12 In order that the result remains stable, a time integration of the image information items determined during the analysis 5 is subsequently effected in a process designated extraction 6. If the integration is carried out for example over 1 second, it extends over 25 images in the PAL format. Thus, the mean brightness, the chrominance, the active pixels and the degree of saturaton are integrated over time t from t to n and the following properties are obtained: Mean value of brightness: FL =L Mean value of frequency: FF F Mean value of amplitude: FM M Mean value of fire chroma pixels: Fc C Mean value of active pixels: FR R 8- Mean value of saturation: Fs S The mean value of the frequency is obtained for example by counting the pixels having the mean brightness L(t).

The frequency caused by the characteristic flicker of a flame is an important quantity for the detection of a flame because it lies in a defined narrow range of generally between 1 Hz and 10 Hz.

In the subsequent process designated pattern recognition 7, the properties obtained during the extraction 6 are used to calculate the probability that a flame is present. In this case, an examination is effected for example for each of the above properties to determine whether the mean value lies above or below a threshold value and the probability is correspondingly set equal to one or equal to zero. An overall probability is then formed from the probabilities of all n properties.

TL F(FL) 1, if FL 8L TL F(FL) 0, if FL 8L and so on for the other properties.

Overall probability H(t): 1/NF Z n (T.WL TF.WF TM.WM C.-Wc TR.WR s.Ws)/NF (lw, w. w cWR +R Sws)/NF F n for wi, it holds true that 0 wi 1, the values wi being determined empirically. Np is the sum of wi over all i.

In the process designated decision 8, as to whether an alarm is triggered is subsequently taken. This process contains an integration during which the overall probability 17(t) is integrated upward over successive images. The integration starts at zero and counts an 9 increment thereto for each 17(t) K (K is a threshold) and subtracts an increment for each 17(t) K. If I(t) designates the value of the integral, the following holds true: I(t 0) 0 If 1(t) K then I(t) I(t-l) o+ (saturated toward if I(t) S+ in all other cases I(t) I(t-1) C_ holds true (saturated towards S_ (usually if I(t) S_) T+ and are generally equal to +1.

The decision as to whether an alarm is triggered is then taken with the aid of the integral I(t): If I(t) P (P is a threshold), an alarm is triggered, in all other cases no alarm is triggered.

The device described has the advantage that, in many applications, it is possible to recourse to already installed video cameras and an installation of special flame sensors is not necessary, which undoubtedly means a reduction of costs. A further reduction of costs results from restricting the evaluation to the image excerpts possibly containing a flame, which enables the computer power to be significantly reduced. It can also be assumed that the evaluation of the said image excerpts is sufficiently robust with respect to disturbances.

Claims

1. A method for detecting flames in a monitoring space, by analysis of at least C one parameter of a radiation that occurs in the monitoring space, said method comprising: Sgenerating a video image of the monitoring space, 00 searching for zones having high light intensitiy and local flicker motion in Ssaid video image, the search for zones having high light intensity and local flicker motion being effected with the aid of an accumulation matrix, which is obtained from the difference images of successive intensity images, said differences being weighted with a weighting factor, the weighting factor specifying the extent to which the difference images influence the accumulation matrix, and said zones being localized and the relevant image excerpts being analyzed with regard to the presence of a flame.

2. A method as claimed in claim 1 wherein the video images are generated with a specific frequency and intensity images are attained therefrom.

3. A method as claimed in claim I1 or 2 including searching for all pixels having a brightness that lie below a predetermined threshold and filtering out moving, dark objects during the formation of the difference images and thus of the accumulation matrix.

4. A method as claimed in claim 3 wherein the coordinates of the brightest pixels are sought with the aid of the accumulation matrix.

A method as claimed in claim 4 wherein an image region of interest which contains the brightest pixel or pixels and is reduced with respect to the original image is defined and analyzed with regard to the presence of a flame.

6. A method as claimed in claim 5 wherein the size of the image region of interest amounts at most to one fiftieth of the size of the original image. COMS ID No: ARCS-176621 Received by IP Australia: Time 15:05 Date 2008-01-24 08/08 2008 FRI 16:08 FAX Smoorenburg Pini 444 IP AUSTRALIA a003/009 00 C

7. A method as claimed in claim 6, wherein the image information items of brightness, chrominance, number of active pixels above a specific intensity threshold, and the saturation, are determined in the image region of interest. 00

8. A method as claimed in claim 7, wherein said image information items are integrated over a specific time and thus over a plurality of images and their mean 00 value is determined in that the mean value of the frequency and the mean value of the amplitude are determined as additional parameters during the integration, and probability for the presence of a flame is calculated for each of said mean values.

9. A method as claimed in claim 8, wherein the probabilities of the mean values are used to calculate an overall probability for the presence of a flame in the reduced image region and said overall probability is integrated over a plurality of images, with an alarm being triggered when a threshold is exceeded by the integrated value. A device for detecting flames in a monitoring space, by analysis of at least one parameter of a radiation that occurs in the monitoring space, said device comprising a video camera, an evaluation stage for the images supplied by the camera, the evaluation stage having a processor with an algorithm for the localization of regions having high light intensity and local flicker motion in the images of the camera and the subsequent analysis of the corresponding image excerpts with regard to the presence of a flame, wherein the algorithm contains a preprocessing process for determining an accumulation matrix for the search for zones having high light intensity and local flicker motion, said accumulation matrix being obtained from the difference images of successive intensity images, said difference images being weighted with a weighting factor, the weighting factor specifying the extent to which the difference images influence the accumulation matrix.

COMS ID No: ARCS-201517 Received by IP Australia: Time 16:08 Date 2008-08-08 08/08 2008 FRI 16:08 FAX Snmoorenburg Plnl 444 IP AUSTRALIA Q004/009 00 12

11. A device as claimed in claim 10, wherein the algorithm contains an image Sobtaining process for obtaining intensity images from the video images generated with a specific frequency. 00

12. A device as claimed in claim 11, wherein the preprocessing process, with _the aid of the accumulation matrix determines the coordinates of the brightest n pixels and an image region of interest is defined which contains the brightest pixel 00 or pixels and is reduced with respect to the original image.

13. A device as claimed in claim 12, wherein the algorithm contains an N analysis process, for the analysis of the image region of interest determining image information items of brightness, chrominance, number of active pixels above a specific intensity threshold, and the saturation.

14. A device as claimed in claim 13, wherein the algorithm contains an extraction process for integrating said image information items over a specific time and thus over a plurality of images and determining the mean values of the image information items, the mean value of the frequency and the mean value of the amplitude being determined as additional parameters during the integration, and the probability for the presence of a flame being calculated for each of said mean values.

A device as claimed in claim 14, wherein the algorithm contains a process of pattern recognition and a process of decision, during which the probabilities of the mean values are used to calculate an overall probability for the presence of a flame in the reduced image region and said overall probability is integrated over a plurality of images and an alarm is triggered in the event of a threshold being exceeded by the integrated value.

16. A method for detecting flame in a monitored zone substantially as described herein with reference to the accompanying drawing. COMS ID No: ARCS-201517 Received by IP Australia: Time 16:08 Date 2008-08-08 08/08 2008 FRI 16:09 FAX Smoorenburg P1int IF AUSTRALIA f1005/009 00 13 C117. A device for detecting flames in a monitored zone substantially as described herein with reference to the accompanying drawing. ;Z 00 COMS ID No: ARCS-201 517 Received by IP Australia: Time 16:08 Date 2008-08-08