Today, Google announced a possible replacement for the worldwide accepted standard for web images. Just like JPEG, Google’s new ‘WebP’ format is a lossy compression standard based on the guts of their WebM video codec (formerly called VP8).
WebP 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 pixels to predict the values in a block, and then encodes only the difference (residual) between the actual values and 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.
So why try to change the world? For a 40% filesize reduction, that’s why. Cutting most of the images in the world in half would be a huge win. According to the Pingdom tools, downloading the main page of VizWorld.com is 360k of data, and 300K of it is Images. Cutting that down to 200k would be a nice start, and doing it worldwide would be huge.
However, JPEG has huge support from both software and browsers. And not all is wine and roses in the WebP world: encoding an image into WebP format takes an average of 8 times longer. However, due to it’s similarity to WebM & VP8, hardware designed to accelerate those standards is suitable for WebP as well.
