How posterization works
Each pixel of a digital image has a red, a green and a blue value between 0 and 255, which allows millions of colors. Posterizing rounds each of those values to the nearest of a few evenly spaced steps. The slider sets how many steps every channel gets, from 2 to 16:
| Levels per channel | Values per channel | Maximum colors |
|---|---|---|
| 2 | 0, 255 | 8 |
| 3 | 0, 128, 255 | 27 |
| 4 (default) | 0, 85, 170, 255 | 64 |
| 6 | 0, 51, 102, 153, 204, 255 | 216 |
| 8 | 8 steps | 512 |
| 16 | 16 steps | 4,096 |
Because the steps are fixed and the same for every image, the result is predictable: two photos posterized at the same level share the same set of possible colors, which keeps a series consistent.
Getting a good poster look
- Start with contrast. Photos with a clear subject and strong lighting give bold, readable shapes. Flat, gray pictures turn muddy.
- Use few levels for graphics, more for photos. 2 or 3 levels gives a pop-art, comic feel with saturated primaries; 5 to 8 keeps faces natural with visible bands.
- Watch skies and skin. Smooth gradients are where the effect shows most. If they look too blocky, add one or two levels.
- Check at full size. The preview is scaled down; banding that looks fine there can look harsher when the image is shown large.
- For a single-color poster, convert to gray first with Black and White Photo, then posterize: you get a clean set of gray steps.
Posterize vs. pixel art vs. halftone
These effects are often confused. Posterize keeps the full resolution and only limits the colors. Image to Pixel Art also shrinks the picture into large square pixels and lets you choose a palette such as Game Boy or PICO-8. Halftone Effect replaces tones with a pattern of dots in one ink color, like newspaper printing.
Formats and batch processing
You can open JPG, PNG, WebP, AVIF, GIF (first frame), BMP and SVG files, plus iPhone HEIC photos. Select several images to posterize them all at the same level; Download saves a ZIP with “-posterize” added to each name (a file whose format changes, such as HEIC to JPG, just gets the new extension).
| You open | You download |
|---|---|
| JPG | JPG (quality 92%) |
| PNG | PNG, transparency kept |
| WebP | WebP (PNG in Safari, which can’t save WebP) |
| HEIC, AVIF | JPG |
| SVG, GIF, BMP | PNG |
Tip: flat colors compress very well as PNG, and JPG compression can add faint noise to the edges between bands, so save as PNG when you need crisp areas of color.
Privacy
Everything happens in your browser: the file is read, posterized on a canvas and saved locally. The site’s security policy only lets the page talk to its own server, and EXIF metadata such as GPS location is not copied into the output.