Resize a WebP

• Decodes the stored picture, redraws it on the new grid and squeezes it back into a WebP at quality 80.
• Turns a lossless WebP into a lossy one, since the only mode the encoder here has is the lossy one.
• Keeps a cut-out subject cut out, because WebP stores its alpha beside the colour data rather than inside it.

• Converts nothing into this format — a JPEG or PNG dropped on the panel comes back in the format it arrived in.
• Carries no lossless switch to turn on; send the file through WebP to PNG when the pixels have to stay exact.
• Chases no byte figure: the dimensions you type decide the size, so use the compressor when a ceiling is the requirement.

1. Add the file and set a width. Drag the .webp onto the panel above, up to 20 MB, then type the width you want. With the ratio lock on, the height follows by itself. Switch to Percent to scale by a fraction instead, or take one of the platform sizes and both fields fill in.
2. Press Resize image. The picture is redrawn at the new dimensions and encoded again as a WebP at quality 80. Because the format select is left on Same as the original, the file type and the extension are unchanged.
3. Check the numbers and download. The panel prints the dimensions it actually produced next to the size before and after, so what the second encode cost is a figure you see rather than one you assume.

A picture has to be taken apart to be made smaller. The stored file becomes pixels again, those pixels are redrawn on a smaller grid, and the result is squeezed back into a WebP at quality 80. That last squeeze is the part worth thinking about, because it is lossy every single time.

Most WebP files have already had one. WebP is what a site serves, which means somebody compressed the image before it ever reached you, and the copy you saved becomes a copy of a copy the moment you resize it. Once is fine and you will not spot it. The habit to avoid is going round again and again, each pass starting from last week’s output — find the largest version that exists and take a single step from there.

WebP has two modes, and this is the one place the difference bites. A file written in the lossless mode stores its pixels precisely, much as a PNG does. The encoder in this build has a single setting, quality 80, and it is the lossy one — so a lossless WebP put through a resize here comes back as a lossy WebP. That is worth saying plainly rather than leaving you to discover it.

On a photograph it is a non-event. On flat artwork with hard edges, held as a lossless master, it is a genuine change, and the answer is to stop treating WebP as the master: send the file through WebP to PNG and work from the PNG instead, which stays exact however many times it is opened.

A WebP normally has a next stop in mind, and that stop has a width. An image dropped into a 720-pixel column has no use for 3000 pixels of picture. A listing photograph is displayed at whatever the marketplace displays it at. A header image is cut to the width of the header. Everything above that number is weight a reader pays for and never sees.

So the working rule is to match the display width, double it if the image has to stay crisp on a high-density screen, and stop. The platform sizes in the panel cover the common social and video frames if you would rather not work the number out, and choosing one sets both fields at once.

The alpha channel is resampled alongside the colour, so a WebP with a cut-out subject comes back still cut out, and the partly transparent pixels along its edge keep their degree of transparency. WebP stores alpha beside its lossy colour data rather than inside it, which is why this holds even though the colour is being written afresh.

The format select above sits on Same as the original, which is what gives you a WebP back with the extension it arrived with. Overriding it in the same pass is allowed: JPEG produces a file almost anything will open, at the price of the transparency, and PNG produces an exact one that will be a good deal heavier. Those two formats have pages of their own as inputs — resize a JPG and resize a PNG.

A batch tab sits beside the single-file one and takes up to 20 files at once, which is the shape this job usually has: a folder of product shots pulled off a site, every one of them needing the same width. One size covers the set, individual files can be pinned to a target of their own, and the results arrive as a single archive.

A single file may be up to 20 MB, and neither side of the finished picture may pass 8000 pixels. The work itself is done by the browser tab you are reading this in: the file is opened where it already sits and the new one is written beside it, so there is no transfer at either end and no second copy of your image anywhere. The output is rebuilt from raw pixels, which is why it carries no EXIF or GPS data. An image big enough to strain what this device can spare is refused before it starts, with the reason.

• The format select reads Same as the original, so a JPEG or PNG dropped here comes back as a JPEG or PNG — this page keeps a WebP a WebP; it does not turn other files into one.