A new image format for the Web
WebP is a new image format that provides lossless and lossy compression for images on the web. WebP lossless images are 26% smaller in size compared to PNGs. WebP lossy images are 25-34% smaller in size compared to JPEG images at equivalent SSIM index. WebP supports lossless transparency (also known as alpha channel) with just 22% additional bytes. Transparency is also supported with lossy compression and typically provides 3x smaller file sizes compared to PNG when lossy compression is acceptable for the red/green/blue color channels.
Webmasters and web developers can use the WebP image format to create smaller and richer images that can help make the web faster.
How WebP works
Lossy WebP compression 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.
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. This palette is continuously updated to re-use recent colors. This compression mode is named "VP8L" and shares some common features with the so-called LZ77 compression algorithm.
A WebP file consists of VP8 or VP8L image data, and a container based on RIFF. The standalone
WebP is supported by a variety of tools. In addition, it is now natively supported in Google Chrome, the Google Chrome Frame plug-in for Internet Explorer, Opera 11.10 and Android Ice Cream Sandwich.
Developers have also added support to a variety of image editing tools. This release also provides a lightweight encoding and decoding library,