Diagram of a black and white enlarger. Set the size, focus and position of the image with the main lights on before getting out the photographic paper. Turn off the main light, and carry out the exposure with the safe light on.
Richard Avedon's notes to his printer. (I've seen this before but I'm glad to see it again so I can pin it and send it to people who say digital is not as “pure” as film. No, the exact steps are not the same but the process is similar. Post-processing has always, and will always, be part of professional photography. A little or a lot depends on the photographer and the vision.)