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Fire Detection Algorithms Using Multimodal ... - Bilkent University

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CHAPTER 2. FLAME DETECTION IN VISIBLE RANGE VIDEO 11and motion recurrence images do not provide a quantitative frequency domainmeasure. On the other hand, wavelet transform is a time-frequency analysis toolproviding both partial frequency and time information about the signal. Onecan examine an entire frequency band in the wavelet domain without completelyloosing the time information [10], [52]. Since the wavelet transform is computedusing a subband decomposition filter bank, it does not require any batch processing.It is ideally suited to determine an increase in high-frequency activity infire and flame colored moving objects by detecting zero crossings of the wavelettransform coefficients.In practice, flame flicker process is time-varying and it is far from being periodic.This stochastic behavior in flicker frequency is especially valid for uncontrolledfires. Therefore, a random model based modeling of flame flicker processproduces more robust performance compared to frequency domain based methodswhich try to detect peaks around 10 Hz in the Fourier domain. In [84], fire andflame flicker is modeled by using HMMs trained with pixel domain features invideo. In this thesis, temporal wavelet coefficients are used as feature parametersin Markov models.Turbulent high-frequency behaviors exist not only on the boundary but alsoinside a fire region. Another novelty of the proposed method is the analysis ofthe spatial variations inside fire and flame colored regions. The method describedin [78] does not take advantage of such color variations. Spatial wavelet analysismakes it possible to detect high-frequency behavior inside fire regions. Variationin energy of wavelet coefficients is an indicator of activity within the region. Onthe other hand, a fire colored moving object will not exhibit any change in valuesof wavelet coefficients because there will not be any variation in fire colored pixelvalues. Spatial wavelet coefficients are also used in Markov models to characterizethe turbulent behavior within fire regions.

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