Why a WebP can still be made smaller
WebP is already an efficient format, but the size of a WebP file depends heavily on the quality it was saved at and on how hard the encoder worked. Editors and exporters often use a safe high quality so that nothing can go wrong. This tool measures how much each image can take before it stops looking like the original, saves it at that quality, and uses a more thorough compression method for the final file.
WebP quality is a number from 0 to 100 that sets how hard the encoder works to keep detail. There is no single right value: 75 to 80 is a common default in tools and editors, and it suits some pictures and not others. A smooth picture can look perfect at 70, and a detailed one can need 90. That is why this tool measures each picture and picks the quality it needs, instead of applying one number to everything.
In our tests, photos exported at quality 90 shrank by 40 to 56 percent when re-saved at the quality they needed. Photos that were already exported at 75 to 80 did not shrink enough to be worth saving again, and a file like that is returned as it is. The tool does not re-save a WebP for a gain of a few percent, because every pass over a lossy file loses a little detail.
Transparency, animation, orientation and metadata
WebP can hold transparency, and it is kept when you compress. The transparent part is stored with its own quality setting, which this tool keeps high, so soft edges and shadows stay clean. If a result looks worse than the original around transparent edges, use High quality.
Animated WebP files are not touched. An animation would become a single picture if it were compressed, so the file is returned exactly as it was, with a note. Use a video tool if you need a smaller animation.
A WebP can also carry a note that says the picture is stored sideways, and browsers do not all obey it. The compressed copy is turned upright for real and carries no note, so it looks the same in every program. With Keep camera details and location switched on, the camera details are copied into the new file with the rotation reset to upright. By default the camera details, date and location are removed, and a WebP that comes back unchanged has them cut out of the file itself.
Lossy and lossless WebP
WebP has a lossless mode, popular for graphics and screenshots, which keeps every pixel but makes bigger files. This tool writes lossy WebP. A graphic saved as lossless WebP can be re-saved as lossy at a high quality for a much smaller file, which is fine for most uses. If you need exact pixels, for example thin lines in a diagram, keep the lossless file or use the PNG compressor, which keeps exact edges.
WebP compared with JPG for the same picture
In our tests at the Balanced level, the same picture saved as WebP instead of JPG came out about 4 to 5 percent smaller for two large, detailed photos, and 20 to 45 percent smaller for smaller, smoother pictures such as a signature, a screenshot or a plain sky. So the gain is largest where JPG wastes the most bytes, and small on big photos full of texture. If you also want to change the format of a JPG or PNG while compressing, choose WebP under Format and compare the result with the JPG one.
Using WebP on a website
Every current browser opens WebP. To stay safe with older software, serve it with a fallback: a picture element can offer the WebP first and a JPG or PNG behind it, and many content delivery networks pick the format automatically. Email clients and upload forms are the places that most often still refuse WebP.