Hi! *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 http://www.lu.se/o.o.i.s/7758 http://www.google.com/profiles/12.yakir ---------------------------------------------- CLASS-L list. Instructions: http://www.classification-society.org/csna/lists.html#class-l