Pixelate an image into a blocky mosaic

How to use Image Pixelate

1. Choose one or more images.
2. Set Block size from 2 to 100 px (it starts at 12 px).
3. Pick Save as. PNG keeps the block edges perfectly crisp; JPEG may smudge them slightly.
4. Press Apply and download the files ending in -pixelated.

What it does and when to use it

Pixelation is the “mosaic” look from TV censorship and from old video games. It is useful for:

• Retro and 8-bit style artwork, posters and profile pictures.
• Teasers, where a product or reveal should be recognisable as a shape but not in detail.
• Reference pictures for cross-stitch, bead or LEGO-style mosaics, where each block becomes one stitch or brick.
• Hiding a whole picture’s detail, such as a background photo you do not have rights to show clearly.

For a smooth soft look instead of hard squares, use Image Blur. To reduce the number of colours as well, follow up with Image Posterize, which gives an even stronger game-art feel.

How it works

The tool works in a Web Worker on your device. Starting at the top-left corner, it walks over the image in squares of Block size × Block size pixels. For each square it adds up the red, green, blue and alpha values of all pixels inside, divides by the number of pixels, and paints the whole square with that average. Squares at the right and bottom edges may be smaller and use their own average.

Worked examples

Counting blocks. A 4000 × 3000 px photo at the default 12 px has 334 blocks across (333 full ones plus one 4 px strip) and 250 down. At 40 px it has 100 × 75 blocks, so the picture reads like a small 100 × 75 pixel image drawn large.

Averaging. We ran the tool’s function on a 13-pixel strip whose red values climb in steps of 20, from 0 to 240. With Block size 12, the first twelve pixels all became 110, their average, and the thirteenth pixel, alone in the last block, stayed 240.

A cross-stitch chart. A 600 × 600 px image with 10 px blocks gives a 60 × 60 grid of colours, ready to count stitch by stitch.

Limits and tips

• Block size is in image pixels, so the same setting looks coarser on small pictures. Resize first with the Image Resizer if you want consistent results.
• Transparent areas are averaged too, so blocks along the edge of a cut-out may become partly transparent.
• No EXIF data is copied to the new file.