Dots, fired one at a time
How Does a Printer Place Ink So Exactly?
A printer turns your page into a grid of dots and fires a speck of ink at each one, thousands of times a second.
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Step 1 of 5
The page is turned into dots first.
Letters and photographs alike are broken down into a grid, and every square is decided: ink here, no ink there. That grid is what gets printed.
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Step 2 of 5
Four inks make every colour.
Ink absorbs light rather than emitting it, so the mixing works the other way from a screen: cyan, magenta and yellow, with black added because mixing three inks makes mud.
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Step 3 of 5
Each drop is fired by a tiny explosion.
In most home printers a resistor boils a speck of ink for a few millionths of a second. The steam bubble shoves one drop out of the nozzle, then collapses and pulls more ink in.
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Step 4 of 5
The head sweeps, the paper steps.
The print head runs left and right laying down a band of dots, then rollers advance the paper by exactly that band's height and it sweeps back.
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Step 5 of 5
Laser printers use static instead of drops.
A laser writes an invisible pattern of charge onto a drum. Powdered toner clings only to the charged parts, transfers to the paper, and is melted on by a hot roller.
A typical inkjet fires drops of about 2 picolitres — you would need roughly 25 million of them to fill a single teaspoon.
The short version
A printer breaks the page into a grid of dots and fires or fuses a tiny amount of colourant at each one, line by line.
Try it yourself
Look at a printed photo through a magnifying glass. The smooth colours turn into separate dots of cyan, magenta, yellow and black.
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