Why a quality slider barely touches a PNG
JPEG and WebP are lossy: a quality setting tells the encoder how much visual detail it may throw away, and that is where the savings come from. PNG has no such dial. It is lossless by design, so every pixel is reproduced exactly and re-encoding mostly rewrites the same information.
That is why a PNG-in, PNG-out "compression" often reports a saving close to zero. Nothing is broken. To get a real reduction you have to change one of the other variables:
| Change | Typical saving | What it costs you |
|---|---|---|
| Resize the dimensions | Up to 90%+ | Nothing, scaling down |
| Convert to WebP | 25–80% | Nothing on modern browsers |
| Convert to JPG | 70–90% on photos | Transparency, and some detail |
| Re-encode as PNG | Usually under 10% | Nothing, but gains little |
Is your PNG a photograph?
If so, the format is the problem. PNG stores photographic content extremely inefficiently, and a photo saved as PNG is routinely five to ten times larger than the same image as JPEG at a quality nobody can tell apart. Send it through PNG to JPG instead, or PNG to WebP if you need the transparency kept. Keep PNG for logos, icons, screenshots and anything with crisp text.
Check the dimensions first
Before compressing anything, it is worth knowing whether the file is simply too large in pixels for where it is used. Our website image checker scans a live page and reports every image's real size against its displayed size, and the image resizer fixes what it finds. Resizing almost always beats compression on an oversized PNG.
Frequently Asked Questions
Why did compressing my PNG barely shrink it?
Because PNG is a lossless format. Re-encoding a PNG as a PNG rewrites the same pixel data, so a quality slider has almost nothing to work with — unlike JPEG, where quality genuinely discards detail. If your PNG came out roughly the same size, that is the format behaving correctly, not the tool failing.
How do I actually make a PNG smaller?
Three things work, in order of impact. Resize it if its pixel dimensions are larger than the space it is displayed in, which is usually the biggest win by far. Convert it to WebP, which keeps transparency and is typically 25 to 80 percent smaller than the equivalent PNG. Or reduce the number of colours, if it is a logo or flat graphic rather than a photograph.
Does converting PNG to WebP lose transparency?
No. WebP supports an alpha channel exactly like PNG does, so transparent areas stay transparent. This is the main reason WebP can replace PNG rather than only JPEG — you get PNG-style transparency at much smaller sizes.
Should my image be a PNG at all?
PNG is the right choice for logos, icons, screenshots, and anything with sharp text or a transparent background. It is the wrong choice for photographs, where JPEG or WebP will be dramatically smaller at quality no one can distinguish. A photograph saved as PNG is one of the most common causes of a needlessly heavy page.
Are my PNG files uploaded to a server?
No. Decoding and re-encoding run in a Web Worker on your own device using WebAssembly builds of the standard image libraries. Nothing is transmitted, which you can confirm by watching your browser Network tab while a file compresses.
Related tools
- Image compressor — the same engine for JPG and WebP too.
- Compress JPG — where the quality slider actually earns its keep.
- Image resizer — usually the bigger win on an oversized PNG.
- How to reduce image file size — the full decision order.