Compress PNG Online — Free & Lossless

PNG compression is trickier than JPEG compression because PNG is a lossless format. There are no quality sliders — you cannot choose to accept visual degradation in exchange for a smaller file. Instead, PNG compression works by using better algorithms to represent the same pixel data more efficiently.

The biggest wins come from eliminating unnecessary colour depth. A PNG that was saved with a 32-bit colour space (8 bits per channel plus alpha) but only uses 64 distinct colours can often be safely converted to an 8-bit indexed PNG with a custom palette, achieving file size reductions of 50–70% with zero perceptible quality loss.

For PNG images on the web — icons, logos, UI elements, illustrations, screenshots — there are several levels of compression available. OptiPic applies PNG encoding using your browser's canvas API, which uses standard zlib compression. For maximum compression, specialised tools like pngquant (lossy palette quantisation) or Zopfli (lossless deflate optimisation) can achieve better results, but for general use, OptiPic's output is excellent.

Converting PNG to WebP is often the most effective approach if you need smaller file sizes. For a logo with transparency, a WebP lossless conversion is typically 20–30% smaller than the equivalent PNG. For photographic PNGs, the difference is even more dramatic.

If you must keep PNG format, the most impactful steps are: strip metadata (OptiPic does this automatically), reduce colour depth for images that do not need 24-bit colour, and ensure you are using progressive/optimised deflate settings. OptiPic handles the last point automatically.