Fire Detection Algorithms Using Multimodal ... - Bilkent University

CHAPTER 6. WILDFIRE DETECTION 87The decision function D 2 (x, n) takes values between 1 and −1 dependingon the values of the Y (x, n), U(x, n) and V (x, n) channel values. The decisionfunction D 2 (x, n) is defined as:D 2 (x, n) ={1 −|U(x,n)−128|+|V (x,n)−128|,128if Y (x, n) > T I−1, otherwise(6.3)where Y (x, n), U(x, n) and V (x, n) are the luminance and chrominance values ofthe pixel at location x of the input image frame at time step n, respectively. Theluminance component Y takes real values in the range [0, 255] in an image andthe mean values of chrominance channels, U and V are increased to 128 so thatthey also take values between 0 and 255. The threshold T I is an experimentallydetermined value and taken as 100 on the luminance (Y) component in thiswork. The confidence level of D 2 (x, n) is −1 if Y (x, n) is below T I . The reasonthat we have the threshold T I is to eliminate dark regions which also have lowchrominance values. Since wildfire smoke regions are mostly colorless, having verylow chrominance values, the decision value approaches to 1 as the chrominancevalues U(x, n) and V (x, n) are around the mean value of 128 for pixels whoseluminance values are greater than T I . Confidence value drops down to −1 forpixels with high chrominance values.6.2.3 Detection of Rising RegionsWildfire smoke regions tend to rise up into the sky at the early stages of the fire.This characteristic behavior of smoke plumes is modeled with three-state HiddenMarkov Models (HMM) in this chapter. Temporal variation in row number of theupper-most pixel belonging to a slow moving region is used as a one dimensional(1-D) feature signal, F = f(n), and fed to the Markov models shown in Fig.6.2.One of the models (λ 1 ) corresponds to genuine wildfire smoke regions and theother one (λ 2 ) corresponds to regions with clouds and cloud shadows. Transitionprobabilities of these models are estimated off-line from actual wildfires and testfires, and clouds. The state S1 is attained, if the row value of the upper-most pixelin the current image frame is smaller than that of the previous frame (rise-up).If the row value of the upper-most pixel in the current image frame is larger than