FAST HUMAN DETECTING USING A CASCADE OF HISTOGRAM OF ORIENTED GRADIENTS Qiang Zhu, Shai Avidan, Mei-Chen Yeh, and Kwang- Ting Cheng In: Computer vision and Pattern Recognition-CVPR’2006 Presenter: Hoang, Van Dung dungvanhoang@islab.ulsan.ac.kr April 28, 2012 Intelligent Systems Lab. Outline Histogram of Oriented Gradients (HOG) Method Variable size block “Integral image” method Training classification Experiments Conclusions. 2 Intelligent Systems Lab. Introduction Paper (*) showed that the system is powerful enough to classify humans by use HOG feature. However, it has high computational cost. This paper try to speed up above method by using AdaBoost, and HOG feature. However, if using original HOG (fix size blocks) is not informative enough to classify at high accuracy. => This paper proposed HOG computing with variable size block. *Dalal, N and Triggs, B.. Histograms of Oriented Gradients for Human Detection. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, Vol. II, pp. 886-893 (2005). 3 Intelligent Systems Lab. Histogram of Oriented Gradients Gradient computation Orientation binning Descriptor blocks Block normalization Gradient computation Gx=I[-1 0 1] Gy=I[-1 0 1]T Gy 61 117 107 176 193 193 Magnitude G Gx Gy 2 2 ac tan( Gy Gx 64 111 133 254 254 234 146 211 214 168 255 255 74 140 254 254 231 195 69 111 148 254 187 126 ) 3 -6 26 78 61 41 85 94 107 -8 62 62 10 29 121 0 -23 -39 4 -77 -100 -66 86 -68 -129 -2 -48 -96 -64 -30 9 72 92 158 190 201 204 Gx Gy Gx Angle G 3 -19 10 -64 14 78 56 46 59 86 17 0 47 69 143 121 -20 -20 65 68 -43 41 87 0 66 180 114 -23 -59 -36 42 79 143 39 -128 -61 20 86 98 43 14 3 Intelligent Systems Lab. Computing HOG within a Region Computing histogram of gradient based on orientation (Using unsigned of orientation (0-1800) and 9 bins) Magnitude 56 46 64 116 63 41 97 117 179 121 65 65 66 74 128 41 90 39 Angle 101 206 132 89 90 134 42 92 172 75 131 62 20 88 99 77 20 78 87 97 66 48 16 1 5 29 36 53 94 18 18 81 67 20 90 105 180 139 119 120 15 139 164 93 121 124 149 103 82 81 102 84 146 45 2 Intelligent Systems Lab. Computed HOG Calculation histogram of orientation gradient within cells, blocks. Accumulation features to construct HOG feature vector. i i F f 1 f h1,1 , ..., h1,9 , ....., ..., h 4 ,1 , ..., h 4 ,9 i 2 , f , ...., f i n i F is the vector feature of image, f i is the vector feature of ith-block and normalizing. 6 Intelligent Systems Lab. Variable-size Blocks Different with original HOG feature, this paper don’t fix size of block. The block size rangers from 12x12 to 128x64 with restrictive ratio between block width and height is (1:1), (1:2), and (2:1). Original HOG: 105 block (3,780 features). This paper: 5,031 block (181,116 features). Intelligent Systems Lab. Discretize Gradients into Bins Discretization each pixel’s gradient magnitude into 9 bins based on their orientation. Computing gradient 8 Intelligent Systems Lab. “Integral Image” Method Using “Integral image” method for rapid compute HOG There are two steps to calculate sum of gradients with in a region . Creation the SAT table. SA T ( x , y ) x y i 1 j 1 g (i , j ) SA T ( x 1, y ) SA T ( x , y 1) SA T ( x 1, y 1) g ( x , y ) SAT(x,y) Calculation a histogram bin of gradient within a region (x,y,w,h) based on SAT S(x,y,w,h)= SAT(x+w-1,y+h-1)-SAT(x-1,y+h-1) SAT(x+w-1,y-1) SAT(x-1,y-1) SAT(x+w-1,y-1)+SAT(x-1,y-1) SAT(x-1,y+h-1) SAT(x+w-1,y+h-1) => HOG within cell(x,y,w,h), we compute S(x,y,w,y) of 9 bin layers, respectively. Intelligent Systems Lab. Training the Cascade Chose one block that is best classification 10 Intelligent Systems Lab. Training the Cascade Each a cascade consists several weak classifiers Each weak classifier used one block. The number weak classifiers of each cascade depend on the training process After “loop fi>fmax”, if Fi> Ftarget is not satisfied, resampling by put false positive sample (from evaluate test) into negative samples for next iteration. 11 Intelligent Systems Lab. Experiments 12 Intelligent Systems Lab. Experiments 13 Intelligent Systems Lab. Experiments 14 Intelligent Systems Lab. Experiments 15 Intelligent Systems Lab. Experiments Figure 6. Comparing the Dalal & Triggs algorithm, a Rectangular filter detector and our cascade of the HoG method. Our method (using either L1 or L2 norms) is comparable to the Dalal & Triggs method, especially when the FPPW goes down. 16 Intelligent Systems Lab. Experiments 17 Intelligent Systems Lab. Conclusions This system used AdaBoost that is up to 70X faster than previous method (Dalal&Triggs). Using multiple sizes block in order to accumulate more features that rich for training and classification. Using “integral image” method that rapid compute features. 18 Intelligent Systems Lab. THANK YOU FOR LISTENING! Intelligent Systems Lab. x1= (x11 x2= (x21 x3= (x31 x4= (x41 ………….. xn= (xn1 x12 x22 x32 x42 x13 x23 x33 x43 …. …. …. …. x1m) x2m) x3m) x4m) xn2 xn3 …. xnm) m3 …… mm) mean m= (m1 m2 20 Intelligent Systems Lab. 450 400 350 300 Using all features that accumulated from sample image. 250 200 150 100 50 0 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 500 450 400 Using only the best features that were selected by training. 350 300 250 200 150 100 50 0 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 21 1 Intelligent Systems Lab.