Converting PNG to WebP

Where PNG came from, and why it is like this

WebP is Google's, and it exists for one reason: images are most of the bytes on most web pages, and Google's business depends on pages loading quickly. It was derived in 2010 from the intra-frame compression of the VP8 video codec, on the reasoning that a single video frame is just an image and video codecs had improved considerably since JPEG was standardised in 1992.

What makes WebP unusual is that it is two formats wearing one file extension. Lossless WebP is a genuine PNG replacement — exact pixels, alpha channel, typically 25–35% smaller than the same image as PNG. Lossy WebP is a JPEG replacement that, unlike JPEG, also supports transparency. A file called .webp could be either, and nothing in the name tells you which.

Is this conversion lossy?

Which answer applies depends on the quality setting. At maximum quality the encoder is asked for lossless output and the pixels round-trip exactly. Below that it is lossy, and its artefacts differ from JPEG's in a way that matters: where JPEG produces visible blocking at edges, WebP tends to smooth detail away instead. Fine texture — fabric, foliage, film grain, skin — quietly disappears rather than becoming blocky.

That is usually preferable at the same file size, and it has one trap. Blockiness looks like damage, so people notice it and dial the quality up. Smoothing looks like a slightly soft photograph, so people do not notice, and a WebP that has been through several re-encodes can end up markedly less detailed than the original without any single step looking wrong.

What happens to metadata, transparency and colour

Transparency survives. This is the main reason to choose WebP over JPEG. The alpha channel is carried across in both lossless and lossy mode, so a logo with a transparent background stays transparent — the thing that makes PNG to JPG go wrong simply does not happen here.

Metadata does not survive the canvas. The WebP format has room for EXIF and ICC profile chunks, but a browser converting through a canvas has already discarded them: the canvas holds pixels. So the format could carry your colour profile and this conversion does not.

Animation is technically possible and practically not. WebP supports animation, but no browser will encode an animated WebP from a canvas — the encoder exposed to web pages writes a single frame. An animated PNG converted here becomes one still frame, the first one.

Why people actually need this

Usually a performance audit. Lighthouse and PageSpeed Insights both flag large PNGs and both name WebP in the recommendation, so the situation is a developer with a list of images and a score to raise. The saving is real: for the flat-colour graphics that tend to be PNGs, lossless WebP is reliably smaller with no visual change at all.

The other situation is a design handoff. A designer exports transparent PNGs because that is what design tools produce, and the images go onto a site where their size is a problem. WebP is the only widely supported format that keeps the transparency and fixes the size, which is why it has become the default answer.

What we measured

This conversion was run end to end before this page was written. Not "should work" — run, with the output checked:

And the ceilings measured for Image converter, the tool that performs it, on the hardware described on the limits page:

Not tested

The page also refuses files above 50 MB before it starts, which is a guard written into the tool rather than something the browser imposes. Why those are different.

When something else is the better answer

If the image is going anywhere other than a web page, WebP is likely the wrong choice — not for technical reasons but for social ones. Support in image editors, print workflows and older desktop software is patchy, and sending someone a .webp attachment is a good way to receive a confused reply. Convert to PNG or JPG for anything a person will open rather than a browser will render.

If you need the smallest possible file and the image has no transparency, a well-compressed JPEG is competitive with lossy WebP and universally supported. The gap between them is smaller than WebP's marketing suggests.

If the PNG is already small — an icon, a sprite, anything under a few kilobytes — converting is not worth the trouble. WebP has a larger container overhead than PNG, and below roughly a kilobyte the WebP version can be the bigger file.