How it works
Turning a photo into a pattern
How many colours, what dithering does, and why the answer is also your shopping list.
This is also the shopping list: 0 colours to buy, and 0 piles to keep separate while you work.
Fewer colours is a shorter shopping list and a flatter picture. More is truer and more piles to keep apart while you work. Most people land between 15 and 30.
Dithering scatters two colours together so your eye mixes them, which smooths a gradient at the cost of a speckled look up close. Good for skies and skin, bad for flat artwork and lettering.
Your photo never leaves the device. The conversion runs in the browser, which is also why it is instant.