If computer screens render different colours by filtering white background light through red, green and blue pixels, and black is the absence of colour, how do computer screens reproduce the colour black?

Question

The most intuitive answer would seem that black pixels get “switched off”, but I know that’s not true because I can tell when a monitor is switched on and off even if the screen is just black. There’s a sort of “black glow” to them.

In: Engineering

Answer 1

Not all screens work this way.

OLED displays don’t have a backlight; they use red/green/blue pixels that are individually self-illuminating. So if that pixel needs to be black, it just doesn’t light up at all, and it really does look black.

But cheaper displays do work with a backlight, and the red/green/blue pixels control how much of the backlight gets through. To display black, a pixel will reduce the light coming through it by the maximum amount possible. Since this isn’t perfect, you actually get a slightly glowing dark gray color instead of black – but you perceive it as black because you’re comparing it to the other colors on the screen. Fancier displays have what’s called “local dimming” where sections of the backlight can be made dimmer or turned off, to make the black areas closer to black.