function H=HOG(Im)
nwin_x=3;%set here the number of HOG windows per bound box
nwin_y=3;
B=9;%set here the number of histogram bins
[L,C]=size(Im); % L num of lines ; C num of columns
H=zeros(nwin_x*nwin_y*B,1); % column vector with zeros
m=sqrt(L/2);
if C==1 % if num of columns==1
Im=im_recover(Im,m,2*m);%verify the size of image, e.g. 25×50
L=2*m;
C=m;
end
Im=double(Im);
step_x=floor(C/(nwin_x+1));
step_y=floor(L/(nwin_y+1));
cont=0;
hx = [-1,0,1];
hy = -hx’;
grad_xr = imfilter(double(Im),hx);
grad_yu = imfilter(double(Im),hy);
angles=atan2(grad_yu,grad_xr);
magnit=((grad_yu.^2)+(grad_xr.^2)).^.5;
for n=0:nwin_y-1
for m=0:nwin_x-1
cont=cont+1;
angles2=angles(n*step_y+1:(n+2)*step_y,m*step_x+1:(m+2)*step_x);
magnit2=magnit(n*step_y+1:(n+2)*step_y,m*step_x+1:(m+2)*step_x);
v_angles=angles2(:);
v_magnit=magnit2(:);
K=max(size(v_angles));
%assembling the histogram with 9 bins (range of 20 degrees per bin)
bin=0;
H2=zeros(B,1);
for ang_lim=-pi+2*pi/B:2*pi/B:pi
bin=bin+1;
for k=1:K
if v_angles(k)<ang_lim
v_angles(k)=100;
H2(bin)=H2(bin)+v_magnit(k);
end
end
end
H2=H2/(norm(H2)+0.01);
H((cont-1)*B+1:cont*B,1)=H2;
end
end