Background: I want to compare two images that are identical in many respects (pixel-wise) but are different in the pixel intensity values they have. I'm aware of the many image comparison methods out there, but I want to keep it very very simple  (for all the image analysists: these two images are artificial and made through the same process with some differences without any spatial translation). 
What I am doing right now: is calculating the euclidian distance between the pixel intensities of the 2 images. The mean of all the distances (if the image is 500*500 pixels then there are 500^2 distances) gives me a measure of how similar those images are. 
My question is: is the euclidian distance really the best option when comparing natural numbers that can only range between 0 and 255, or should I use some other measure of distance or transform the pixel intensities first?

Thanks in advance!

Yakir L. Gagnon, PhD student
The Lund Vision Group
Tel  +46 (046) 222 93 40
Cell +46 (073) 753 63 54
Fax +46 (046) 222 44 25
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