Both, but lots of science. In particular, convolution is linear so if you know what you want a bright dot (a single pixel—a delta function) to look like, then t

Both, but lots of science. In particular, convolution is linear so if you know what you want a bright dot (a single pixel—a delta function) to look like, then that is your kernel. Want a dot to look like a fuzzy blob? Then your kernel should be a fuzzy blob (Gaussian blur). Want a dot to turn into a positive blip on the left and a negative one on the right (an x-derivative), then (-1, 0, 1) is your buddy (I lied in the symmetric case: it needs to be flipped).