MATLAB: Obtaining greyscale image as nxm matrix

image

i have a gray scale image and wish to obtain values in matrix form.(as in an n x m matrix).This is what i have attempted :
I = imread('cameraman.tiff');
[xmax,ymax]=size(I)
for x=0:1:xmax
      for y=0:1:ymax
          I(x,y)
      end
  end
but am getting an error:
??? Subscript indices must either be real positive integers or logicals.

Best Answer

I is already a matrix, so what do you mean by obtain values in matrix form?
Matrix indexing in matlab starts at 1, so your loops should be
for x = 1:xmax
  for y = 1:ymax
    %whatever you want to do
  end
end
Note that if indexing started at 0, then your loop would have to terminate at xmax-1, not xmax.
Also note that indexing is in the form (row, column), so if you use the standard convention that x is horizontal and y vertical, then your indexing should be:
I(y, x)
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