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Google open sources JPEG assassin

GPEG claims 40% more smallness

Google has open sourced a new "lossy" image format known as WebP — pronounced "weppy" — claiming it can cut the size of current web images by almost 40 per cent.

CNet revealed the format with a story late this morning, and Google soon followed with a blog post describing the technology, which has been released as a developer preview. WebP is derived from VP8, the video codec Google acquired with its purchase of On2 Technologies earlier this year and promptly open sourced as part of the new WebM format.

It's no secret that Google is on a mission to make the web faster — in any way it can. The faster the web, the more cash Google rakes in. WebP is yet another speed play, with Google claiming that images and photos make up about 65 per cent of the bytes transmitted per web page today.

"Most of the common image formats on the web today were established over a decade ago and are based on technology from around that time. Some engineers at Google decided to figure out if there was [sic] a way to further compress lossy images like JPEG to make them load faster, while still preserving quality and resolution," the company says. "WebP... promises to significantly reduce the byte size of photos on the web, allowing web sites to load faster than before."

Like JPEG, WebP uses "lossy" compression, discarding small portions of an image as it works to save space. Basically, Google has applied techniques from VP8 video intra-frame coding to image coding, before adding a container based on the Resource Interchange File Format (RIFF). The container format accounts for only about 20 bytes per image, Google says, and of course, it's extensible, so you can store metadata as well.

Mirroring the way VP8 encodes video key frames, WebP using predictive coding, which predicts the values in a block of pixels using the values in neighboring blocks, and then encodes only the difference between the actual value and the prediction. The difference is known as the residual, and the residuals typically contain many zeros, which can be compressed more effectively, according to Google. WebP also uses variable block sizes.

Google has tested the format by re-encoding 1,000,000 existing web images, mostly JPEGs, GIFs, and PNGs, and it saw a 39 per cent reduction in average file size.

In addition to open sourcing the encoder, Google has released a command-line tool for converting images to the new format, and it says it's working on a WebKit patch that will provide native WebP support for its Chrome browser. It's also in discussions with other browser makers over the technology. Mozilla and Opera have already joined Google's WebM effort. ®

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