# What does it mean when cross correlation between two images occur at negative coordinates

I am using Matlab normxcorr2 to calculate the cross correlation between several images, something like what has been done here: in Matlab documentation. There are some of the examples that I get negative values for xoffSet and yoffSet, but I am not sure what it means when these values are negative. Another issue, is practical since I need to give these xoffSet and yoffSet values as an input to coordinates of rectangle in an image, but since these are negative, the function throws an error. I googled it but no success in finding something that can explain such thing. I was thinking of just putting zero instead of negative values, but I'm not sure if that's a right approach. I would appreciate if someone can explain about the meaning of such negative values and how I can substitute such negative values with appropriate quantities.

• Welcome to DSP.SE! It sounds like the coordinates your call to peak is returning is in the padding area added by normxcorr2. Are you sure you are giving the yoffSet = ypeak-size(onion,1); call the correct image (i.e. your onion patch image). – Peter K. Sep 13 '17 at 16:05
• Thank you for your comment! Basically, to find yoffSet, and xoffSet, I need to subtract the first and second dimensions of the template image (the image with the smaller size), respectively, from ypeak and xpeak. So, the answer is yes. – Miranda Sep 13 '17 at 16:11