Google has introduced a new format for compressed images, WebP, which it says can reduce files sizes by as much as 40%.
WebP — pronounced “weppy” — is intended to supplant JPEG, the de facto standard for web images, by allowing image sizes to be significantly reduced while preserving image quality. Richard Rabbat, Google product manager, says this should considerably reduce the time it takes for image-heavy web pages to load.
“Images and photos make up about 65% of the bytes transmitted per web page today. They can significantly slow down a user’s web experience, especially on bandwidth-constrained networks such as a mobile network.”
To speed things up, Google turned to the VP8 video codec that it acquired last year, applying video compression techniques to still images.
“We applied the techniques from VP8 video intra frame coding to push the envelope in still image coding,” says Rabatt.
Google also adapted the RIFF container format for storing image metadata. The container adds just 20 bytes to the file size, but can be used to store any metadata that is required.
The company has published a gallery that displays equivalent JPEG and WebP images side-by-side, with the WebP images displayed as PNG files to ensure that they can be viewed in current browsers. The web page also provides links for further information about the format.
To have any chance of replacing the entrenched JPEG, WebP will require support in all the major web browsers — even Google Chrome’s support is pending, in cameras and in image processing and editing software. Even the JPEG organisation failed when it tried to replace its offspring with the JPEG-2000 format and Microsoft announced a similar effort to Google’s several years ago, without success.
That said, WebP will offer one thing that JPEG doesn’t, which may tip the balance for website authors. Google says that it plans to add support for transparency, via an alpha channel. Currently that can only be accomplished using the PNG files, which, since they emply lossless compression, can be significantly larger than the corresponding JPEG or indeed WebP image.
