Gaussian blur (filter to blur images)

There was this time I made a pizza and wanted to put a fancy photo of it on social media. So I blurred the background to make it look posher. The one on the left is the original and the one on the right is blurred.

This article unfortunately does not examine how to make the pizza, but will ask the other important question - How does blurring the background work?

Background What is a blur filter?

A filter takes an image, processes it and returns an output. In this case, the processing is the...