Image Processing 101
Slightly related, but I had a small epiphany when taking a class on DSP on Coursera. The kernel that is used to blur an image and that which is used to remove the treble/high frequencies from an audio sample are identical, except one is in 2 dimensions and the other is in 1. And this makes perfect sense! A low pass filter removes high frequencies, and sharp edges are high frequencies in the 2D plane.<p>TFA only mentions Gaussian blur, but a Gaussian blur is just a moving average, with "closer" pixels being valued higher, plus a smooth falloff. When you replace each value with an average of its neighborhood, you "soften" the transitions.