Google推出新的图片格式WebP，挑战JPEG，让互联网更快
官方英文原版
A new image format for the Web
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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 pixelsto predict the values in a block, and then encodes only the difference (residual) between the actual valuesand 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. Itcan 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 libwebp library serves as a reference
implementation for the WebP specification and is available at this git repositoryand
as a tarball.
WebP support
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 alightweight encoding and decoding library, libwebp and
command line tools cwebp and dwebp for
converting images to and from the WebP format. The full source code is available on the download page.
Convert your favorite collection from PNG and JPEG to WebP by downloading the precompiled cwebp conversiontool
for Linux, Windows or
Mac OS X.
Tell us your experience on the project's mailing
list.
后续会翻译成中文的版本，今天时间不够！！！