Short · Phones
How does Portrait Mode fake a blurry background?
A phone's tiny lens keeps almost everything sharp, so Portrait Mode estimates how far away each part of the picture is, then blurs it by its distance from the focus point.
Try it yourself
Opens Portrait Mode Lab. Change the same thing yourself.
Transcript
How does your phone fake that blurry background? A big camera blurs it with optics, focusing at just one distance. A phone's tiny lens keeps almost everything sharp. So the phone estimates how far away each part of the picture is, building a depth map. Now move the focus point. Whatever sits at that distance stays sharp, and the farther anything is from it, the more software blurs it. Stray hairs at the edges give the trick away. Follow to see how the world works.