RGB

In more detail

Each of the three is a figure saying how hard that light is driven. All three off is black, all three at full is white, and equal amounts of the three is a grey. Mixing light adds up to white, which is the opposite of mixing ink: put the printing inks on top of one another and you arrive at a muddy brown.

Three bare numbers say nothing about what the colour looks like, because no two screens are driven alike. sRGB is the answer everybody settled on: an ordinary screen, described once and for all, so that the same three numbers mean the same colour on your machine and on your customer's.

What it does on a real document

A document that will be read on a screen — a statement, a form, a manual — says its colours this way, and carries the description of the screen they were chosen against. That description is what makes them survive the journey to somebody else's machine.

A document going to a press does not. Ink on paper cannot reach every colour a screen can, so a job separated for printing states its colours in inks from the start rather than leaving the conversion to whoever opens the file.

Where it comes from, and why

The three come from the eye rather than from engineering: it answers to three bands of light, so three lights are enough to match any colour a person sees. Television was built on that, then the computer screen. sRGB was written down in 1996 to describe the middling screen of the day, and it is still what a file is taken to mean when it says nothing.

See it on a finished document

Grey, screen and printing colours The same numbers, said so they mean something The rules behind this word, and the texts they are read from