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mpotoole

So what is the difference between using a convolution vs. correlation to do image filtering? Well, here's one example.

Click here for full resolution image. Note that image is 200 x 200, kernel is 9 x 9.

We have a image of a night sky (a bunch of bright stars) and I'm interested in applying an "arrow" filter for artistic effect. Notice that when I perform a convolution, the arrows are pointing in the same direction as my kernel. When performing a correlation, the arrows are actually pointing in the opposite direction. So the sign used in this case matters a lot.

What would you expect to see if the arrow was pointing up instead of right?

mariecurie

Convolution would show arrows pointing up and correlation would show arrows pointing down?

mpotoole

@mariecurie Exactly.