WebP is a new image format that provides lossy compression for photographic images. In a large scale study of 900,000 web images, WebP images were 39.8% smaller than jpeg images of similar quality.
A WebP file consists of VP8 image data, and a container based on RIFF. The standalone libwebp library serves as a reference implementation for the WebP specification and is available at this git repository and as a tarball. Webmasters and web developers can use the WebP image format to create smaller and better looking images that can help make the web faster.
Did you know? WebP is pronounced "weppy".
How WebP works
WebP uses predictive coding to encode an image, the same methodology 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 (residual) between the actual values and the prediction.
The residuals typically contain many zero values, which can be compressed much more effectively. The residuals are then transformed, quantized and entropy-coded as usual. WebP also uses variable block sizes.