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01 October 2010, 10:22

Google announce WebP as an alternative to JPEG - Update

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Zoom Google's comparison of a JPEG and WebP image and compression
Source: Google
Google has announced WebP, an image format based on the WebM video codec technology, which it says saves 40% of bandwidth compared with JPEG encoded images. Google believes that, as images and photos make up about 65% of the bytes transmitted per web page, the 40% reduction in image size could offer a dramatic improvement in web performance. With most image formats in use created over ten years ago and based on even older technology, Google saw the opportunity to apply the intra-frame algorithms in the VP8 codec, which it open sourced in May, to a still image format.

Using VP8's intra frame coding and a lightweight container, based on RIFF, the company created a format which has as little as 20 bytes overhead, while allowing authors to save as much meta-data as they need to store. To test the new format Google then took a million images, mostly JPEGs, from the web and re-encoded them in WebP "without perceptibly compromising visual quality". It found there was an average reduction in file size of 39%. Some of the resulting images are available in a gallery alongside the original images, for wider comparison.

Currently, only the webpconv converter utility can import and export images to WebP format which uses libvpx, the VP8 codec SDK. There is no image viewer or browser support available at the moment, but Google says it is working on a patch for WebKit which will add native support for WebP in a future version of its Chrome and Chromium browsers. It also plans to add support for alpha channels (transparency) in a future update to WebP.

The WebP project has a page on Google's "Let's make the web faster" site where webpconv source code and build instructions are available along with a Google Code site for collaboration on the code. WebP appears to be licensed under a BSD licence with a royalty free patent rights grant to Google's patents on the VP8 technology and uses the leptonica libraries under their own liberal licence.

Update - Jason Garrett-Glaser (also known as 'Dark Shikari'), main developer for the free H.264 encoder x264 has carried out his own analysis of WebP. He says that besides WebP only supporting 4:2:0 chroma sub-sampling (JPEG also supports 4:2:2 and 4:4:4), a JPEG encoder is clearly superior, at least from first tests where WebP delivered images that were "by far the worst of the bunch". On the basis of these results, Garret-Glaser asks the question "Is Google nuts?". Although he sees potential in the file format and believes a better encoder could be made for the format, he thinks that libvpx, at least in its current form, is "an awful encoder". He suggests that Google make a good encoder first, then promote it as better than the alternative, as doing it the other way around "doesn't quite work as well".


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