# How to get average intensity from a selected image window

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Tania on 26 Nov 2014
Answered: Abdullah on 8 Feb 2017
Hi everyone,
I have got the intensity value like below from the selected image window.
66 61 54
65 59 55
60 54 60
How can I get the average of this numbers.
Thanks

Guillaume on 26 Nov 2014
First of all, usually x is used to refer to the horizontal dimension and y to the vertical one. That's the 2nd and 1st dimension of your matrix respectively. So to access pixel (x, y), you need to do:
value = I(y, x);
Because of that, I usually don't use x and y as a variable, but row and col.
Secondly, to access a rectangle of pixels, don't use a loop (particularly as you keep overwriting the scalar value), but just use matrix indexing:
values = I(y-g:y+g, x-g:x+g)
Finally to get the average of all values in a matrix:
meanvalues = mean(values(:));

#### 1 Comment

Tania on 26 Nov 2014
Excellent, Works perfect

Abdullah on 8 Feb 2017
How to let x and y read the row and column ?