Light the subject, not the background
Adobe's guide sums it up: the key is making sure your subject is more lit than your backdrop. It suggests apertures around f/1.4–4 (up to about f/6 if the background still shows), ISO 100–125, and black fabric or seamless paper behind the subject [1]. Moving the subject further from the backdrop helps too — light falls off quickly with distance.
When the room won't cooperate
At events, in offices or outdoors you can't control the background. Cutting the subject out and compositing it “over” pure black — the operation Porter and Duff defined for the alpha channel [2] — gives the same look after the fact. Hair and soft edges matter most here, because any leftover light background shows as a bright halo against black.
Black vs transparent
If you'll place the portrait on different colours later, keep a transparent PNG master — PNG stores the soft edge alpha that makes hair look natural [3] — and export black versions from it.



































