# What is the betwwen [i,j] and [u,v] in explinations of correlation and convolution (picture attached)?

I don't know how to write 'summation' symbol here hence posting the picture.

Can someone explain to me the difference between i,j and u,v in this explanation of correlation and convolution?

I know this discussion must have taken place somewhere but it is difficult to look for such discussion by keyword 'correlation' and convolution'.

I have already referred to the following posts: 1. Difference between correlation and convolution on an image? 2. What is the difference between convolution and cross-correlation?

• You can write TeX (or TeX-alike) code directly in your question! $\sum a^2 becomes$\sum a^2$, and $$\sum_{a=0}^{100} a^2$$ becomes $$\sum_{a=0}^{100} a^2$$. Try it out! also, youtube videos are usually not the best source to find information about math subjects – I've found several ones that are plain wrong but had literally millions of views. – Marcus Müller Mar 11 '19 at 8:25 • Not quite sure what you're asking, though.$u$and$v$are the indices of the summation, whereas$i,j\$ are the point at which you evaluate your convolution and correlation. – Marcus Müller Mar 11 '19 at 8:26
$$[i,j]$$ are your spatial coordinates and $$[u,v]$$ are summation indices.
The difference between correlation and convolution is simply the sign: correlation has $$i+u$$ and convolution has $$i-u$$.