obtaining greyscale image as nxm matrix

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.

Answer 1

[Guillaume]

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)

[Terry McGinnis]

this is what i had already tried dude.

I = imread('cameraman.tiff'); [xmax,ymax]=size(I)

for x=0:xmax-1

    for y=0:ymax-1

        I(x,y)
    end
end

but im still gettin the same error

??? Subscript indices must either be real positive integers or logicals.

Error in ==> codetest5 at 8 I(x,y)

and by matrix form i mean this: [ a b c d; e f g h; i j k l]

[Guillaume]

Did you actually read my answer?

matlab indexing starts at 1, so for y = 1:ymax

matlab uses row, column indexing, so I(y, x)

I still have no idea what you mean by matrix form. I is already a matrix. Ca you show an example of the output you want as valid matlab syntax?

[Terry McGinnis]

k sorry got it.

What i meant was in a row and column form,looking like this:

[Guillaume]

double click on I in the workspace browser and you'll set its value in the variable editor

Or just type I in the command window

Or use the pixel region tool

[Terry McGinnis]

italic what i really need to do is implement a 2d gaussian fitting.I am modifying the code given in:

http://in.mathworks.com/matlabcentral/fileexchange/37087-fit-2d-gaussian-function-to-data

where i need to put in the values of data obtained from my image. But I am not able to modify the code as stated in the comment by Nathan neff-mallon .Im a stuck in this part:

change line 38 to [X,Y] = meshgrid(x,y); where x and y a vectors with your x an y axis points change line 47 to Z = zdata; where _ _ zdata is a length(x) by length(y) matrix with the data you wish to fit such that zdata(i,j)=z(x_i,y_j). _ _

[Guillaume]

It's a completely different question to your original one, so you should start a new question.

[Terry McGinnis]

thanks Guillaume