A new image format for the Web

from: https://developers.google.com/speed/webp/






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A new image format for the Web





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A new image format for the Web

WebP is a new image format that provides lossless and lossy compression forimages on the web. WebP lossless images are
26% smaller in size comparedto PNGs. WebP lossy images are
25-34% smaller in size compared to JPEGimages at equivalent SSIM index. WebP supports lossless transparency (alsoknown as alpha channel) with just
22% additional bytes. Transparency isalso supported with lossy compression and typically provides 3x smaller filesizes compared to PNG when lossy compression is acceptable for
thered/green/blue color channels.

Webmasters and web developers can use the WebP image format to create smallerand richer images that can help make the web faster.

How WebP Works

Lossy WebP compression uses predictive coding to encode an image, the samemethodology used by the VP8 video codec to compress keyframes in videos.Predictive coding uses the values in neighboring blocks of pixels to predictthe values in a block, and then
encodes only the difference (residual) betweenthe actual values and the prediction.

The residuals typically contain many zero values, which can be compressed muchmore 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 toexactly reconstruct new pixels. It can also use a local palette if nointeresting match is found. This palette is continuously updated to re-userecent colors. This compression mode is
named "VP8L" and shares some commonfeatures with the so-called
LZ77 compression algorithm.

A WebP file consists of
VP8 or
VP8L image data, and a containerbased on
RIFF. The standalone

libwebp

library serves as a referenceimplementation for the WebP specification, and is available fromour git repository and as a
tarball.

WebP Support

WebP is natively supported in Google Chrome and the Opera browser, and bymany other tools and software libraries.

Developers have also added support to a variety of image editing tools. Thisrelease also provides the lightweight encoding and decoding library

libwebp

and the command line tools

cwebp

and

dwebp

forconverting images to and from the WebP format. The full source code isavailable on the
download page.

WebP Converter Download

Convert your favorite collection from PNG and JPEG to WebP by downloading theprecompiled

cwebp

conversion tool for
Linux, Windows or Mac OS X.

Tell us your experience on the project's
mailing list.

本页面中的内容已获得知识共享署名 3.0 许可，并且代码示例已获得
Apache 2.0 许可；另有说明的情况除外。有关详情，请参阅我们的网站政策。

上次更新日期：十月 9, 2015

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