Why PNG is the safest way out of WebP
WebP is a delivery format: browsers love it, and almost everything else tolerates it at best. PNG is the reverse, unspectacular on a web page but accepted by every editor, office suite, presentation tool, print workflow and upload form ever written. When a WebP has to leave the browser and go somewhere unpredictable, PNG is the conversion that cannot go wrong, because it is lossless and it keeps transparency exactly.
The conversion decodes the WebP in your browser, passes the raw pixels to a Web Worker, and encodes them with a WebAssembly PNG encoder. There is no quality slider, because there is nothing to choose: every pixel is written out as it was decoded. Nothing is uploaded at any point.
Two kinds of WebP, one kind of result
WebP files come in a lossless and a lossy variety, and the distinction matters for what your PNG represents.
- A lossless WebP, typical of screenshots, stickers and graphics exported from design tools, becomes a PNG that is pixel-for-pixel identical to the original source. This is a true round trip.
- A lossy WebP, typical of photos saved from websites, becomes a PNG that faithfully preserves the WebP's compression artefacts. The softening already present in the WebP is frozen in place, but nothing further is lost, and the file will never degrade again no matter how many times you save it.
In both cases the alpha channel survives intact, including soft anti-aliased edges and partial transparency. That is the main reason to choose this page over WebP to JPG, which throws transparency away.
What else changes
Animated WebP, common in sticker packs from Telegram and WhatsApp, is reduced to its first frame; the browser decoder does not expose the others, so the PNG is a still image. Any EXIF or XMP block inside the WebP is not copied, and an embedded colour profile is applied during decoding and then discarded, so the PNG is plain 8-bit sRGB. Pixel dimensions are unchanged.
The PNG encoder writes a straightforward 32-bit RGBA file. It does not analyse the image and reduce it to a 256-colour palette, which a dedicated PNG optimiser would do for flat graphics and which can cut such files by half or more. For most purposes that difference is irrelevant, but if the PNG is heading for a website, run it through Compress image or consider whether the WebP should simply stay a WebP.
Expect a much larger file
Typical numbers, which depend on the content:
- A 512x512 sticker of 30 KB as WebP usually becomes a 200 to 350 KB PNG.
- A 1920x1280 photo of 180 KB as WebP usually becomes 3 to 4.5 MB, since PNG cannot compress photographic noise.
- A 1440x900 interface screenshot stored as lossless WebP at 210 KB often lands at 400 to 700 KB, a smaller jump because flat colour compresses well in both formats.
If the size increase is a problem for where the file is going, and transparency is not needed, a JPG at quality 90 will be far smaller. If transparency is needed and size still matters, the honest answer is that PNG is the only universal option and the size is the cost of universality.
Practical limits
Your browser must be able to decode the WebP. Every current browser can, but Safari before version 14 and some very old Android WebViews cannot, in which case the tool reports a failure instead of producing an empty file. Very large images are bounded by canvas memory on the device, which on phones can mean a limit around 30 to 50 megapixels. Batch conversion is supported; files are processed one after another, each with its own download. For background on why a browser-only tool has these limits and no others, see what nothing is uploaded actually means.