I always said that one of these days I was going to go through all of our de-focus options and figure out the differences/strengths.

I still plan on doing this when I get some down time but it came up today with my assistant that i was telling them not to use Gaussian for de-focus and they asked me what the difference was!


So lets narrow this down to just the blur node. What is the difference between Gaussian and defocus.

I bet this has something to do with convolution filters but I don’t really know.

yea all blur types are convolve filters.

Defocus just uses a different function for the convolve a gaussian function

I think that convolving your image with a circular shape would result in defocus type effect, which is what defocus does

Gaussian blur is basically a low pass filter, so it kills high frequencies, (something something fourier transformation if a gaussian is another gaussian) . I think I fell asleep in college when we talked about those filters…

(If I say filter I dont mean instagram filters but the technical term)

If you have nuke you can take a look at the convolve node and feed it different 2dimensional images, I think for gaussian it would be the Finite-Impulse - response of the gaussian function but i wouldnt know how this looks like would be a nice experiment though.

Ha , I should have known the gaussian kernel as it was printed on our banknotes …

Filters are crazy complex (again not the instagram filters, different thing!)


The way I like to think about it is defocus replaces each pixel with a shape (aka a “convolve filter”), blur averages the pixels, so a defocus will take a very bright pixel like a point light and turn it into a large and still bright circle, whereas a blur will mush everything together.