How to compress a PNG: lossless first, fewer colours second
PNG is a lossless format, so it has no quality slider like JPG. That changes how you make one smaller. There are three honest options: repack the same pixels more efficiently, reduce the image to 256 colours, or use fewer pixels. Sometimes the right answer is a different format altogether. This guide explains each and shows how to do them in the Image Compressor without uploading the file.
Option 1: lossless optimisation
Many PNGs are saved quickly rather than compactly. A lossless optimiser tries different filtering and compression strategies and keeps the smallest file that decodes to exactly the same pixels. Screenshots and exported graphics often get noticeably smaller; files that were already optimised barely change.
This is what the compressor does by default with a PNG when you do not resize, rotate or convert it: the PNG setting is Lossless, and the result note says the pixels were preserved. If the optimised file is not smaller, the original is kept. Metadata may remain in this mode.
Option 2: Smaller PNG with 256 colours
A photograph or a gradient can contain hundreds of thousands of distinct colours. Reducing them to a palette of at most 256, with dithering to hide the steps, often cuts a PNG to a fraction of its size while keeping transparency. Interface screenshots, icons, diagrams and flat illustrations usually look the same; photographs, soft shadows and smooth gradients can show banding.
Choose PNG → Smaller file — 256 colours in the Compress section. It works on images up to 8 megapixels and is lossy, so compare the result at 100% before you download, paying attention to gradients and anti-aliased edges around transparent areas.
Option 3: fewer pixels
File size follows pixel count. A 2880 × 1800 screenshot from a high-density laptop display has more than five million pixels; shown on a web page at 1440 pixels wide, half the width is enough, and a quarter of the pixels remain. Add Resize and choose Longest side or a width that matches where the image will be shown.
A target size works with PNG only through this route. Because PNG has no quality setting to search, a target is met by reducing dimensions, and only if you tick Allow smaller dimensions. With the tick off, a PNG that is over the target is reported as missed rather than silently shrunk.
When PNG is the wrong format
- Photographs: a photo stored as PNG is often several times larger than the same photo as JPG or WebP at good quality. If the destination accepts JPG and you do not need transparency, convert.
- Photos with transparency: WebP keeps the alpha channel and is usually much smaller than PNG. Most browsers and modern apps accept it; some upload forms do not.
- Screenshots with small text and graphics: keep PNG. JPG smears sharp edges and text; the 256-colour PNG option is the better way to save space.
- Logos and icons that will be scaled: if you have the SVG original, use that. PNG is a fixed number of pixels.
A quick decision
- Add the PNG to the compressor and run it with the default Lossless setting. If the saving is enough, you are done and the pixels are identical.
- If not, switch PNG to Smaller file — 256 colours and compare. Keep it if gradients and edges look right.
- If the image is larger than it will ever be displayed, add Resize as well.
- If it is a photo, try Format → JPG or WebP instead and compare the sizes.
All of this runs in your browser. The PNG is not uploaded, and you can process up to 20 files in one batch and download them as a ZIP.