Binarizing a normalized image is not working properly

I have this code to binarize a normalized DTI medical image, it's not working, and I don't understand where is the problem

i

ii=24;
fname = ('SOME_PATH');

F_Name = fopen(fname);
IMG = fread(F_Name, '*float');
fclose(F_Name);    

IMG = reshape(IMG,256,256,50);
MX = max(max(max(IMG)));
IMG = IMG/MX;

GM_INDX = IMG(108,148,24);

          for l=1:256
              for m=1:256
                  for n=1:50

                      if (IMG(l,m,n) == GM_INDX)
                          IMG(l,m,n)=1;
                      else
                          IMG(l,m,n)=0;
                      end

                  end 
              end
          end
  figure, imshow((IMG(:,:,iii))); title('MD.DAT');

Answer 1

[Image Analyst]

Probably because it's floating point and there may be only 1 pixel, if any, that match. See the FAQ: http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

Try this instead of the triple for loop

tolerance = 0.01; % Whatever.
IMG = IMG > GM_INDX - tolerance & IMG < GM_INDX + tolerance;