How Pixelation Actually Works: Shrink, Then Blow Back Up

It's not drawing squares directly

The chunky, blocky look of a pixelated image might suggest a program is deliberately drawing a grid of solid-colored squares over the original. In practice, the classic pixelation effect used almost everywhere is a much simpler two-step trick that doesn't involve drawing shapes at all.

Step one: shrink the image down

The image is first resized down to a tiny version — for example, a 600×400 photo might get shrunk to just 50×33 pixels. At that tiny size, each remaining pixel is naturally an averaged blend of a whole block of the original image's pixels, since resizing algorithms blend source pixels together when reducing size.

Step two: enlarge it back up without smoothing

That tiny image is then scaled back up to the original dimensions, but with image smoothing turned off. Normally, enlarging an image blurs neighboring pixels together to fake extra detail; with smoothing disabled, each of the tiny image's few pixels is instead blown up into a large, sharp-edged, solid-colored square — which is exactly the blocky mosaic look everyone recognizes as "pixelated."

Why block size controls the effect strength

Shrinking to a smaller intermediate size (fewer, bigger blocks when scaled back up) produces a stronger, chunkier effect, while shrinking less aggressively keeps more detail and produces a subtler mosaic — which is exactly what a "block size" slider controls.

Try it yourself

Our Pixelate Image tool applies exactly this shrink-then-enlarge technique to any photo, with an adjustable block size.