What Black Keeps
Dark frames give up most of the picture on purpose, and hold on to the little that is left.
A dark photograph is not a photograph missing information. Low-key work hands most of the frame to black and keeps a thin edge of light on whatever matters. The meter inside the camera argues with that, since it wants to push black toward grey, so shooting dark usually means dialling exposure compensation down and letting the shadows stay where they are.
Shadows are the most fragile part of a file. Noise, colour casts and banding all live down there, and lifting them two stops is enough to make a picture look dirty. Convincing dark frames are almost always dark at the shutter rather than dark afterwards.
On a screen the difference becomes literal. On an OLED panel true black means pixels that never light up, so a dark wallpaper draws less power and leaves the icons somewhere to stand. An image that is black in a clean way is one of the few you can keep for a week without noticing it.
