IISpeed extends IIS with the capability to automatically rewrite images to WebP for browsers that support it (at the time of writing about 57%). For browsers that do not support WebP, images will still be optimized using the original file format. All these optimizations are performed on the fly when the webserver is delivering them, and don't have any impact on your workflow.
Next to WebP transcoding, other image optimizations include:
- Converting jpeg to progressive - Patrick Meenan just published some real nice insights on this
- Rescaling images to the size specified in css/html
- Insert image dimensions in the html when not present
- Stripping color profiles and meta data
- CSS background spriting
- Converting png and gif to jpeg
- Recompression using configurable quality settings
Optimizing images can really enhance the experience of users on your website, as it can greatly decrease the total weight of a page. This is especially true for mobile users and low bandwidth connections.