JPG to WebP

Converting JPG to WebP is the one case where you are compressing something that has already been compressed. The detail JPEG discarded is gone before this tool sees the file, so the honest goal is a smaller download rather than a better picture. On typical photographs WebP reaches the same perceived quality at a noticeably lower size, which is why it is the usual choice for images served to browsers.

How it is calculated

canvas.toBlob(callback, "image/webp", quality)

The JPEG is decoded to pixels and re-encoded as WebP at the quality you pick. Because this is a second lossy pass, a very low quality setting shows artefacts sooner than it would on an untouched original.

Source: MDN HTMLCanvasElement.toBlob() — quality is a number between 0 and 1 for lossy formats

Questions people ask

Does converting twice make the image worse?

Slightly, yes. Both JPEG and WebP are lossy, so re-encoding adds a second round of approximation on top of the first. At quality 80 and above the difference is hard to see, but repeatedly converting the same file back and forth will visibly degrade it.

How much smaller will the file be?

It depends on the picture, and this tool shows you the actual before and after size rather than promising a number. Photographs with smooth gradients tend to gain the most; images that were already heavily compressed gain the least.

Does the EXIF data survive?

No. The browser decodes the image to raw pixels and re-encodes it, which drops camera metadata, GPS coordinates and orientation tags. That is a privacy benefit when publishing, but keep the original if you rely on that information.

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