%computes spectral teture of an image
function [srad,sang,S]=specxture(f)
S=fftshift(fft2(f));
S=abs(S);
[M,N]=size(S);
x0=M/2+1;
y0=N/2+1;
rmax=min(M,N)/2-1;
srad=zeros(1,rmax);
srad(1)=S(x0,y0);
for r=2:rmax
   [xc,yc] =halfcircle(r,x0,y0);
   srad(r)=sum(S(sub2ind(size(S),xc,yc)));
end
[xc,yc] =halfcircle(rmax,x0,y0);
sang=zeros(1,length(xc));
for a=1:length(xc)
    [xr,yr] =radial(x0,y0,xc(a),yc(a));
    sang(a) =sum(S(sub2ind(size(S),xr,yr)));
end
S=mat2gray(log(1+S));