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Copy pathcalc_sift_descriptor.m
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calc_sift_descriptor.m
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function [descriptor]=calc_sift_descriptor(gradient,angle,x,y,scale,main_angle,d,n)
histlen=(d+2)*(d+2)*(n+2);
hist=zeros(1,histlen);
cos_t=cos(-main_angle/180*pi);
sin_t=sin(-main_angle/180*pi);
exp_scale=-1/(0.5*d*d);
hist_width=3*scale;
radius=round(hist_width*(d+1)*1.414/2);
[M,N]=size(gradient);
radius=min(radius,round(sqrt(M*M+N*N)));
cos_t=cos_t/hist_width;
sin_t=sin_t/hist_width;
radius_x_left=x-radius;
radius_x_right=x+radius;
radius_y_up=y-radius;
radius_y_down=y+radius;
if(radius_x_left<=0)
radius_x_left=1;
end
if(radius_x_right>N)
radius_x_right=N;
end
if(radius_y_up<=0)
radius_y_up=1;
end
if(radius_y_down>M)
radius_y_down=M;
end
sub_gradient=gradient(radius_y_up:radius_y_down,radius_x_left:radius_x_right);
sub_angle=angle(radius_y_up:radius_y_down,radius_x_left:radius_x_right);
X=-(x-radius_x_left):1:(radius_x_right-x);
Y=-(y-radius_y_up):1:(radius_y_down-y);
[XX,YY]=meshgrid(X,Y);
c_rot=XX*cos_t-YY*sin_t;
r_rot=XX*sin_t+YY*cos_t;
Rbin=r_rot+d/2-0.5;
Cbin=c_rot+d/2-0.5;
%gaussian_weight=exp((c_rot.^2+r_rot.^2)*exp_scale);
[row,col]=size(sub_angle);
for i=1:1:row
for j=1:1:col
rbin=Rbin(i,j);cbin=Cbin(i,j);
if(rbin<=-1 || rbin>=d || cbin<=-1 || cbin>=d)
continue;
end
obin=(sub_angle(i,j)-main_angle)*(n/360);
%mag=sub_gradient(i,j)*gaussian_weight(i,j);
mag=sub_gradient(i,j);%ÕâÀï²»Óøß˹ȨÖØ
r0=floor(rbin);
c0=floor(cbin);
o0=floor(obin);
rbin=rbin-r0;
cbin=cbin-c0;
obin=obin-o0;
if(o0<0)
o0=o0+n;
end
if(o0>=n)
o0=o0-n;
end
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
v_r1 = mag*rbin; v_r0 = mag - v_r1;
v_rc11 = v_r1*cbin; v_rc10 = v_r1 - v_rc11;
v_rc01 = v_r0*cbin; v_rc00 = v_r0 - v_rc01;
v_rco111 = v_rc11*obin;v_rco110 = v_rc11 - v_rco111;
v_rco101 = v_rc10*obin; v_rco100 = v_rc10 - v_rco101;
v_rco011 = v_rc01*obin; v_rco010 = v_rc01 - v_rco011;
v_rco001 = v_rc00*obin; v_rco000 = v_rc00 - v_rco001;
idx = ((r0+1)*(d+2) + c0+1)*(n+2) + o0+1;
hist(idx) =hist(idx)+ v_rco000;
hist(idx+1) =hist(idx+1)+ v_rco001;
hist(idx+(n+2))=hist(idx+(n+2)) +v_rco010;
hist(idx+(n+3)) =hist(idx+(n+3))+ v_rco011;
hist(idx+(d+2)*(n+2)) =hist(idx+(d+2)*(n+2))+v_rco100;
hist(idx+(d+2)*(n+2)+1) =hist(idx+(d+2)*(n+2)+1)+ v_rco101;
hist(idx+(d+3)*(n+2)) =hist(idx+(d+3)*(n+2))+ v_rco110;
hist(idx+(d+3)*(n+2)+1) =hist(idx+(d+3)*(n+2)+1) +v_rco111;
end
end
descriptor=zeros(1,n*d*d);
for i=0:d-1
for j=0:d-1
idx = ((i+1)*(d+2) + (j+1))*(n+2)+1;
hist(idx) =hist(idx)+ hist(idx+n);
hist(idx+1) =hist(idx+1)+ hist(idx+n+1);
for k=1:n
descriptor((i*d + j)*n + k) = hist(idx+k-1);
end
end
end
%% Feature vector normalization
descriptor=descriptor/sqrt(descriptor*descriptor');
descriptor(descriptor>=0.2)=0.2;
descriptor=descriptor/sqrt(descriptor*descriptor');
end