This plugin makes it possible to load and save files using the new WebP image format. (http://code.google.com/speed/webp/)
When saving images in this format, you will be able to specify a quality factor that can range from 0 to 100. The higher the number, the larger the file produced and the better the quality of the image.
Since at the time of writing there were no provisions for alpha channels in WebP images, all images loaded with this plugin will not have an alpha channel. As well, when saving images, you will be prompted to flatten the image if it contains an alpha channel.