WebP or .webp (pronounced “weppy”) is an image format that employs both lossy and lossless compression. It is developed by Google, based on technology acquired with the purchase of On2 Technologies. As a derivative of the video format VP8, it is a sister project to the multimedia container format WebM. WebP related software is released under a BSD license.
The following section is from Google Developers:
Using WebP, webmasters and web developers can create smaller, richer images that make the web faster. WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller than comparable JPEG images at equivalent SSIM quality index. Lossless WebP supports transparency (also known as alpha channel) at a cost of just 22% additional bytes. For cases when lossy RGB compression is acceptable, lossy WebP also supports transparency, typically providing 3× smaller file sizes compared to PNG.
How WebP Works
Lossy WebP compression uses predictive coding to encode an image, the same method used by the VP8 video codec to compress keyframes in videos. Predictive coding uses the values in neighboring blocks of pixels to predict the values in a block and then encodes only the difference.
Lossless WebP compression uses already seen image fragments in order to exactly reconstruct new pixels. It can also use a local palette if no interesting match is found.
A WebP file consists of VP8 or VP8L image data, and a container based on RIFF. The standalone
libwebp library serves as a reference implementation for the WebP specification and is available from our git repository or as a tarball.