Cross-correlation coefficient confusion

I wanted to write a program in matlab to calculate the correlation coefficient between a template (with smaller n) and a larger original picture. My question is, how do I generate a correlation picture if the size of the template and the original picture 开发者_JAVA技巧is different? I understand that there is a function xcorr that I can use in matlab, but I wanted to program this myself. Thank you very much!

I believe the idea is to compute the correlation between the template and all possible subimages of the same size in the original picture, sort of like 2D convolution. The function you are looking for in MATLAB is XCORR2 part of the Signal Processing Toolbox.