PNG files can be significantly smaller without changing a single pixel. The secret is that most image editors save PNGs with suboptimal compression settings. Specialised tools apply better compression algorithms to achieve 30-70% size reduction with zero quality loss.
The fastest method is fwip's compression tool. Drop your PNG file and get a smaller version back. The tool applies optimised compression filters and removes unnecessary metadata while keeping every pixel identical to the original. It runs locally in your browser — no upload required.
For even more aggressive lossless compression, tools like OptiPNG, PNGcrush, and ZopfliPNG try thousands of compression configurations to find the smallest possible encoding. The file remains pixel-perfect, but compression takes longer. ImageOptim (Mac) wraps several of these tools into a simple drag-and-drop interface.
If you're willing to accept some quality loss for dramatically smaller files, lossy PNG tools like pngquant reduce the colour palette from millions to 256 colours. This can shrink files by 60-80% and looks indistinguishable from the original on most graphics and screenshots. It's not truly "PNG compression" — it's colour quantisation — but the visual result is excellent for web use.
The biggest win is often the simplest: resize the image to the dimensions you actually need. A 3000px PNG used as a 300px thumbnail on your website should be resized first, then optimised.