Fire Detection Algorithms Using Multimodal ... - Bilkent University

CHAPTER 4. SHORT RANGE SMOKE DETECTION IN VIDEO 57Figure 4.1: Image frame with smoke and its single level wavelet sub-images.Blurring in the edges is visible. The analysis is carried out in small blocks.images are computed, then the energy value, e(l 1 , l 2 ), should be computed usingall wavelet sub-images of the R, G, and B color images. In our implementation,sub-images are computed from the luminance image only and the block size istaken as 8 by 8 pixels.Let B represent a background image built-up in time according to the IIR-typebackground update filter described in Section 2.2.1. Let B v (x, y) = |B LH (x, y)| +|B HL (x, y)| + |B HH (x, y)| represent a composite image containing high-frequencyinformation corresponding to the background image B obtained by the samesingle-level 2-D discrete wavelet transformation operation as for I v (x, y). In asimilar manner, local energy values, e B (l 1 , l 2 ), of the composite image for the backgroundimage can be computed as e B (l 1 , l 2 ) = ∑ (x,y)∈R iB v (x + l 1 K 1 , y + l 2 K 2 )where R i represents a block of size (K 1 , K 2 ) in the wavelet sub-image of thebackground.These local energy values, e I (l 1 , l 2 ) and e B (l 1 , l 2 ), corresponding to currentand background images are compared with each other. If there is a decrease inenergy value e B (l 1 , l 2 ) of a certain block at location (l 1 , l 2 ), then this means thatthe texture or edges of the scene monitored by the camera no longer appear assharp in the current image of the video, as they used to be. Therefore, the imageregion in the viewing range of the camera corresponding to (l 1 , l 2 )-th block couldbe covered with smoke. One can set up thresholds for the comparison. If a certainlocal background energy value e B (l 1 , l 2 ) drops below a pre-determined threshold,