Two ways to shrink a PNG
PNG files are lossless, so they can’t simply be saved at lower quality like a JPG. This tool offers two different methods, chosen with the colour setting.
Colour reduction (the default). Most PNGs store every pixel in full 24-bit colour, with an extra 8 bits for transparency, even when the image only uses a few hundred distinct colours. The tool analyses the image and builds a palette of up to 256 colours by repeatedly splitting its colour range where the colours are most spread out, so the palette follows the colours the image actually uses. Every pixel is then mapped to its nearest palette colour, transparency included, and the file is saved as a compact palette PNG where each pixel takes one byte instead of four. This commonly shrinks screenshots, icons, logos and illustrations by 60–85% in about a second.
Lossless only. The pixels are left exactly as they are. Instead, oxipng tries many PNG filter and compression strategies and keeps whichever produces the smallest file. Savings are smaller, typically 5–50% depending on how the PNG was first saved.
Choosing a colour setting
- 256 colours is visually identical to the original for nearly all screenshots and graphics.
- 128 or 64 colours suit flat icons, simple logos, diagrams and charts. Check gradients in the preview, since fewer colours show banding sooner.
- Lossless only keeps every pixel exactly. Use it for pixel art, medical or scientific images, images with long smooth gradients, or files that will be edited further.
When PNG isn’t the right format
If the PNG is a photo, a lossy format will be far smaller than any PNG. Convert it to JPG for sharing, or to WebP for a website if it needs transparency. PNG is best for images with flat colours, text and sharp edges.
How to use it
Pick a colour setting, then choose or drop your PNG files. Each one is processed in turn. Click the preview to compare it with the original over a checkerboard background, which shows that transparency is intact, then download files one by one or as a ZIP.
Questions
Is PNG compression lossless?
The "Lossless only" setting is. The colour settings reduce the image to a palette of 256 or fewer colours, which is a small, usually invisible change that makes files much smaller.
Is transparency kept?
Yes, including soft edges and shadows. The palette stores transparency for each colour, so cut-out logos and icons stay clean.
Why do smooth gradients show bands after compressing?
A palette of 256 colours can't hold every shade in a long, smooth gradient, so nearby shades merge into visible steps. Choose 256 colours if you used fewer, use "Lossless only", or for photos use JPG or WebP instead of PNG.
Will it work with large screenshots?
Yes. Colour reduction usually takes about a second, even for big screenshots. "Lossless only" is slower, a few seconds for large images, because it tries many compression strategies on your device.
Last reviewed 30 October 2026