How the WebP encoder is chosen
WebP was released by Google in 2010 and has two internal modes. The lossy mode borrows intra-frame prediction from the VP8 video codec. The lossless mode (called VP8L) is a separate algorithm that predicts pixels and applies colour transforms. A lossy WebP can still carry transparency, stored as a separate alpha plane. This converter decodes your PNG or JPG with the browser, paints it on a same-size canvas, and calls the canvas encoder with the type image/webp and your slider value. That slider runs from 10% to 100% and starts at 90%.
The page does not let you pick lossless WebP. The browser's canvas encoder decides the mode, and in practice a quality value below 100% yields a lossy file. Moving the slider triggers a new conversion and updates the size on the download button.
Worked example
Take a 1600×900 PNG hero image of 1.1 MB with a soft gradient and a transparent rounded corner. At 90% the WebP will usually be a few hundred KB and keep the transparent corner, where a JPG would have needed a white fill. Drop to 75% and it often falls to under 200 KB, but banding in the gradient is the first thing to appear, so look at the preview before downloading. The saving is not guaranteed: a tiny 120×120 icon can come out larger than its PNG, because WebP's headers and prediction do little for a handful of flat-colour pixels.
Format comparison
| JPG | PNG | WebP | |
|---|---|---|---|
| Transparency | No | Yes | Yes, even when lossy |
| Animation | No | No (APNG is separate) | Yes, in the format itself |
| Lossless mode | No | Always | Optional |
| Safari support | Always | Always | Display since Safari 14 (2020) |
Limits and gotchas
- Your browser must be able to encode WebP. Chrome, Edge and Firefox can. Safari has historically been unable to export WebP from a canvas, in which case the canvas API hands back a PNG instead. The tool checks what the browser actually produced: if it is not a WebP, the download is named
.pngand a notice above the button says so, rather than saving a PNG under a.webpname. Try another browser if you need a real WebP. - Animated input becomes a still. A GIF or animated WebP is drawn as its first frame only, so the output has no animation.
- Metadata is dropped. EXIF, ICC profiles and thumbnails are not copied through the canvas.
- Old software may reject the file. Some email clients, print shops and CMS uploaders still refuse WebP. If a form refuses it, convert it back with WebP to JPG or WebP to PNG.
- Converting an already-compressed JPG adds a second lossy step. If you still have the original, convert that.
For the full picture on choosing formats and sizes for page speed, read How to Compress and Convert Images for the Web.