Compress PNG

This tool makes PNG files smaller without changing a single pixel. That distinction matters, because most tools advertised as PNG compressors quietly do something else entirely.

What most "PNG compressors" actually do

The large, well-known PNG compression services achieve their impressive percentages by reducing your image to a palette of at most 256 colours, then dithering to disguise the loss. That is quantisation, and it is lossy. On photographs and gradients it produces visible banding; on screenshots with anti-aliased text it softens the letters.

It is a legitimate technique and often a good trade, but it is not what "lossless" means, and it is rarely disclosed clearly. If you have ever compressed a PNG and felt the result looked slightly off, this is why.

What this tool does instead

Breezo runs oxipng, a lossless PNG optimiser compiled to WebAssembly. It works entirely on how the pixels are encoded, not on the pixels themselves: it tries different per-row filter strategies, re-compresses the data stream more aggressively, and strips metadata chunks that carry no image information.

The output is bit-identical to the input as an image. Open both in any editor and difference them — the result is pure black. Nothing was approximated.

How much it actually saves

Lossless optimisation cannot compete with quantisation on raw percentages, but it does far better than most people expect, because a great many PNG files in the wild are written carelessly by screenshot tools and export dialogues.

Measured on our own reference images: a 1600×1000 screenshot went from 92 KB to 47 KB, a 48% reduction with identical pixels. A flat-colour graphic went from 46 KB to 41 KB. A photographic image went from 1,154 KB to 849 KB, a 26% reduction — although for a photograph you should be asking whether it needs to be a PNG at all.

When PNG is the wrong format anyway

If the image is a photograph, no amount of lossless optimisation will make PNG competitive. The same photograph that optimises to 849 KB as a PNG is 72 KB as a quality-75 JPG. Lossless compression simply has very little to exploit in natural photographic detail.

Keep PNG when you need transparency, pixel-exact reproduction, or crisp text and hard edges. For photographs, convert to JPG or WebP instead — the gain is an order of magnitude larger than anything optimisation can offer.