What is a WebP file?

WebP is a binary format, meaningful only to a program that knows it. It stores a grid of pixels, so enlarging it past its own resolution softens it. It is used for the web and handing a finished file over.

The extension is .webp, and the full name is WebP Image. Both matter less than what the file can hold, which is what the rest of this page is about.

Google published it in 2010. The specification is RFC 9649.

Age is worth knowing here for one practical reason: the older a format is, the more programs have had time to learn it.

It is published in full, so anyone can implement it from the document rather than by inspection, which is why it turns up in so many programs and why files written twenty years ago still open. A published specification is not the same thing as a royalty-free one: where a format wraps a codec, the patent licensing is a separate question the standard does not settle.

WebP stores its content exactly. Saving it again changes nothing, so it can be opened, edited and re-saved as often as you like without accumulating damage — which is what makes it a working format rather than a delivery one.

WebP carries an alpha channel, so a logo keeps its soft edges over whatever sits behind it instead of arriving in a white box.

WebP can store an animation rather than a single still. That is worth knowing before converting one: a target that holds one frame keeps the first and drops the rest, usually without saying so.

Up to 8 bits per channel. It can work in RGB and YCbCr, the model video and JPEG compress in.

Eight bits per channel is what a screen shows and what nearly every delivery format carries.

WebP cannot describe an image larger than 16,383 pixels on a side. That is far beyond an ordinary photograph and well within reach of a stitched panorama or a high-resolution scan, which is exactly when people meet it.

Adobe Photoshop, GIMP and Squoosh read it, and so do most programs of the same kind.

If a file will not open, the format is rarely the problem — it is more often that the program predates it. Converting to something older is the reliable way past that, and it is what the rest of this site is for.

Every current browser reads it.

That makes it a safe thing to put on a page or attach to a message without wondering what the other end has installed.

WebP can hold EXIF, XMP and ICC profiles.

Whether any of it survives a conversion depends entirely on the target, and the honest answer is usually "some of it".

WebP is meant to be handed over rather than worked in. Editing one is possible and rarely pleasant; the sane approach is to change the source and export again.

WebP has a lossy mode and a lossless mode, and they are genuinely different compressors. Lossy WebP competes with JPEG and discards detail to get small. Lossless WebP competes with PNG and keeps every pixel exactly. Both produce a `.webp` file and nothing in the name distinguishes them.

This is why the question "does WebP lose quality" has no single answer, and why advice about the format contradicts itself constantly. The honest reply is another question: which mode. A photograph on a website is almost certainly lossy; a logo with transparency is probably lossless.

Almost nobody sets out to make a WebP. They save an image from a web page — a product photo, a recipe picture, something to send to a colleague — and find a file their photo viewer refuses, their document editor rejects and their print service will not accept.

The site was not being awkward. WebP is 25 to 35 per cent smaller than JPEG at the same visible quality, and for a page serving millions of images that is a bandwidth bill rather than a preference. The format is doing its job; the problem is that its job ended at the browser and the file kept going.

Google released WebP in 2010, derived from the VP8 video codec — the still-image equivalent of a single video frame. It arrived alongside WebM and for the same reason: a royalty-free alternative to formats encumbered by patents.

Adoption took a decade because Safari held out until 2020. Until then a website using WebP needed a JPEG fallback for a substantial share of visitors, which removed most of the benefit. Once Safari shipped support, adoption moved very quickly, which is why WebP files started appearing in people’s downloads folders around 2021 and not before.

It predicts each block from its already-decoded neighbours before encoding the difference, which is a technique JPEG’s 1992 design has no equivalent for. The result is roughly a third fewer bytes at the same visible quality, and noticeably better behaviour at low quality settings where JPEG produces obvious blocking.

The same caution applies as to any lossy format: it discards data on every save. A WebP re-encoded from a JPEG has been through two lossy passes and is worse than either would have been alone. Convert from the best source you hold, once.

Lossless WebP typically lands 20 to 30 per cent smaller than PNG on the same image, with every pixel identical. For screenshots, logos, diagrams and icons on a web page that is a straightforward saving with no trade at all.

It also supports transparency in both modes, which is the capability JPEG lacks entirely. Lossy WebP with an alpha channel is a genuinely useful combination — a photographic image with soft transparent edges, at a size PNG could not approach — and it has no equivalent among the older formats.

WebP does animation, and it is dramatically better than GIF: full colour instead of 256, proper alpha transparency instead of one-bit, and files commonly a fraction of the size. Every current browser plays them.

Its weakness is everything that is not a browser. Chat applications, social platforms and image viewers frequently accept an animated GIF and refuse an animated WebP, which is why GIF survives despite being worse in every measurable respect. For anything longer than a few seconds, a video file beats both.

Every browser reads WebP now, and so do current Windows, macOS, Android and iOS. The refusals are concentrated elsewhere: older desktop photo software, some document editors, print services and photo labs, a good number of upload forms whose accepted list was written before 2020, and older televisions and e-readers.

The pattern is that anything web-facing handles it and anything else may not. Before converting, it is worth confirming the destination really is on that list — a surprising amount of WebP conversion is done pre-emptively for software that would have accepted it.

AVIF, built on the AV1 video codec, compresses better again — commonly 20 per cent smaller than WebP at matched quality, with wider colour and higher bit depth. Browser support is now broad, and websites are beginning to serve it the way they began serving WebP five years ago.

WebP retains an advantage in encoding speed and in support outside the browser, where AVIF is where WebP was in 2018. The likely outcome is the same story repeating: a better format arriving, taking years to become safe, and producing a new wave of files people cannot open locally.

JPG when the image is a photograph going somewhere that will not take WebP — expect a somewhat larger file and no visible difference at a good quality setting. PNG when the image has transparency or is a screenshot, diagram or logo, since JPG would flatten the transparency and blur the edges.

The conversion runs inside your browser tab, so nothing is uploaded and there is no size or count limit beyond your own memory. That matters for the common case, which is not one image but a folder of them saved from a site and needed somewhere else.