What lossless compression does
Most compressors make files smaller by throwing detail away. This one doesn’t. It looks for waste in how the image is stored and re-packs the very same pixels more efficiently, so the result decodes to exactly the same image, pixel for pixel. Your PNG stays a PNG, your JPG stays a JPG, and the file keeps its name, so you can drop it straight back where it came from. If you want the biggest possible savings and don’t mind switching format, the WebP compressor goes much further. For the trade-offs, see lossless vs lossy.
How each format is compressed
| Format | What we do | Typical saving |
|---|---|---|
| PNG | Re-filters and re-deflates the image data with oxipng, and reduces bit depth or palette only when it is exactly representable. | 10–60% |
| JPG | Re-codes the existing compressed data with jpegtran from mozjpeg: optimal Huffman tables and progressive scans. The image is never decoded and re-encoded, so there is no generation loss. | 5–15% |
| GIF | Re-packs frames and LZW data with gifsicle. Colours, frame timing and looping are untouched. | 0–10% |
| WebP | Lossless WebP is re-encoded with libwebp at high effort. Lossy and animated WebP can only lose metadata, as re-encoding them would change pixels. | 0–50% |
| BMP / TIFF | No useful lossless compression of their own, so they are converted to an optimised PNG with identical pixels. | 50–95% |
A same-format result is never larger than your upload. If an image is already optimally compressed, the tool tells you so and hands back your original file unchanged.
Metadata: what’s removed and what’s kept
Hidden metadata that doesn’t affect how the image looks is removed: camera make and model, GPS location, editing software, timestamps, text comments and XMP. That makes files smaller and safer to share. Anything that does affect how the image looks is kept: the embedded colour profile (so colours stay accurate) and the orientation (so portrait photos don’t turn sideways).
Frequently asked questions
Does lossless compression change my image at all?
No. Every pixel decodes exactly as before, including the colours of fully transparent pixels. Only the way the file is stored changes, plus the removal of hidden, non-visual metadata.
Why is my file only a little smaller?
Lossless compression can only remove storage waste, so savings depend on how efficiently the original was saved. Photos exported by phones and cameras usually shrink 5–15% as JPG; PNGs saved by design tools often shrink by a third or more. For dramatic reductions, use the WebP compressor or lossy JPG compression.
Are animated GIFs and WebPs supported?
Yes. Animated GIFs are optimised with every frame, delay and loop setting intact. Animated WebPs and animated PNGs are kept as they are, apart from removing metadata.
Is there a size limit?
Files up to 200 MB are accepted. Very large images take longer because all the work happens on your own device, one image at a time.