What does converting JPG to WebP actually do?
JPEG discards detail the human eye is least likely to notice, which is why a photo can shrink by 80–90% with no obvious visual difference. The trade-offs are permanent: there is no alpha channel, and every re-save recompresses the image, so repeated editing slowly degrades it. WebP was designed to replace both JPG and PNG on the web: lossy mode typically beats JPEG by 25–35% at matching quality, lossless mode beats PNG by around 25%, and both modes support an alpha channel. Every current browser supports it, though some older desktop software still does not. Converting JPG to WebP therefore re-encodes the same content under a different set of rules — the pixels are decoded from the source image and written out through the destination encoder. Nothing is uploaded: the decode-and-re-encode cycle happens on your own machine.