How to recompress a still WebP
Load one still WebP, set the quality, and export. The quality slider runs from 1 to 100 and starts at 82. The panel shows the original and the recompressed image side by side along with the output size and a savings percentage, so you can see both halves of the trade before committing.
The savings figure can come out negative. Re-encoding an already-compressed image at a higher quality than it was originally saved at makes it larger, and the panel will tell you so rather than hiding it.
A preset select sits next to the slider with Balanced, Smaller file, and Max quality options. It is worth being precise about what it does: it nudges the quality value before encoding, subtracting 3 on Balanced, subtracting 8 on Smaller file, and leaving it alone on Max quality. It is a shortcut for moving the slider, not a separate compression effort setting.
- Open one still WebP in the browser
- Set the quality, or use a preset to nudge it
- Compare the before-and-after size
- Export the recompressed WebP locally
The lossless toggle, honestly
The lossless checkbox forces the quality to 100. Whether that produces a genuinely lossless WebP depends on your browser, because the encoding is done by the browser built-in WebP encoder rather than by a bundled codec. In Chromium, quality 100 is the setting that triggers the lossless mode, so it works there. Other engines may simply encode at their highest lossy quality instead.
For a logo, an icon, or flat interface artwork, that mode is genuinely worth trying, because images with few colors and hard edges often come out smaller as lossless WebP than as lossy, and they come out perfect. For a photograph, lossless is a large file for no visible gain.
If the browser hands back something other than WebP data, which older Safari builds have been known to do, the tool detects it and tells you rather than saving a mislabeled file. Chromium and Firefox are the reliable places to run this.
What to expect at each quality level
Around 80 is the useful default for a photograph. WebP holds up well there, and pushing to 90 costs real bytes for a difference that is difficult to see at normal viewing size. Below about 60, banding starts to appear in skies and gradients before it appears anywhere else, so those are the images to check first.
Recompressing an already-lossy WebP is a losing trade, and it is worth saying plainly. WebP is lossy, so a second pass throws away more detail for a modest size gain, and the quality lost cannot be recovered at any setting. If you still have the original PNG or JPG, encoding once from that is strictly better than recompressing the WebP.
One more thing our compression study turned up: WebP is not automatically smaller than JPEG. On phone photos it can produce a file no smaller than a well-tuned JPEG. Compare the two rather than assuming, especially when the source came straight off a camera.
- Quality 80 is a reasonable default for photographs
- Below 60, check skies and gradients for banding
- Re-encoding an existing WebP costs quality for little size