convert from to binary

a=imread('coin.png');  #read th image
b=double(a);   # convert into double
s=size(a);    # store size of image in a
cc=zeros(s(1),s(2)); #new empty image
acc=0;   #sum
for i=1:s(1)
         for j=1:s(2)
           acc=acc+b(i, j); #calculate the accumaltion number
         endfor
endfor
th=acc/(s(1)*s(2));  # threshould > 1 white mmm  < 0 black
for i=1:s(1)
  for j=1:s(2)
    if b(i, j)>=th
      cc(i, j) = 1;
    else
      cc(i, j)=0;
      endif
     endfor
    endfor
imshow(cc)