Compress PNG files
Two ways to shrink a PNG: Smart reduces the image to at most 256 well-chosen colours (the technique popularised by pngquant and TinyPNG), and Lossless re-packs every pixel more efficiently with OxiPNG. Transparency is kept either way.
- No upload: runs in your browser
- Batch + ZIP download
- No sign-up, no watermark
Smart PNG vs lossless PNG
Smart vs lossless PNG | Smart (default) | Lossless |
|---|
| How it works | Builds a palette of up to 256 colours (Wu’s quantiser), maps each pixel to it with Floyd–Steinberg dithering, then stores it as an 8-bit indexed PNG with OxiPNG | Keeps every pixel; OxiPNG tries better filters, colour types and compression settings |
| Typical saving | Large on screenshots, UI, charts and illustrations | Small to moderate; large only if the original was saved carelessly |
| Visible change | Usually none on flat graphics; slight grain in smooth photo gradients | None, the pixels are identical |
| Transparency | Kept, including soft edges | Kept |
Choose the mode under Advanced → PNG output. If you set a target size in KB for a PNG, Kilomill steps down through smaller palettes (256, 128, 64 … colours) and, if that is still too big, smaller dimensions.
When PNG is the wrong format
PNG is ideal for screenshots, logos, diagrams and anything with sharp edges, text or transparency. For photographs it is the wrong tool: even a smart PNG of a photo is usually several times larger than a good JPG or WebP. If your PNG is a photo without transparency, convert it with PNG to JPG or PNG to WebP instead.
Tips for smaller screenshots
- Crop away toolbars and empty space first with Crop image; fewer pixels is the biggest saving.
- High-DPI (Retina) screenshots have twice the pixels in each direction. If they are only for documentation, scale them to 50%.
- Dithering can be noticed in large smooth gradients; switch to Lossless for those images.
Questions and answers
Does compressing a PNG lose quality?
Smart mode reduces the number of distinct colours, which is lossy but rarely visible on graphics and screenshots. Lossless mode keeps every pixel exactly the same.
Will transparent backgrounds stay transparent?
Yes. Both modes keep the alpha channel, including semi-transparent edges. Only converting to JPG removes transparency (you can choose the background colour under Advanced).
Why did my PNG get only a little smaller?
It was probably already optimised, or it is a photo with millions of colours where the palette has to work hard. Try WebP, which supports transparency and handles photos much better.
Is this the same as TinyPNG?
It uses the same idea (colour quantisation into an indexed PNG) with different software, and it runs on your device instead of uploading your files to a server.
Is there a limit on file size or number of images?
There is no upload limit because there is no upload. The practical limit is your device’s memory: images up to 100 megapixels (and 16,384 pixels per side) are accepted. Large batches are processed a few at a time.
Are my images uploaded to a server?
No. The images are read and compressed by code running in this browser tab, and the results are created in your device’s memory. Nothing is sent anywhere, which you can confirm in your browser’s developer tools (Network tab) while you work. See Privacy.