JBIG images

I discovered years ago that there is a lossless image format called JBIG. It's used in fax messages, and while it can be used with color images, the common use is with bilevel (aka black and white) images. When saving a scan of a document, book page, or anything else which is (or originally was) b/w, using JBIG will save about 30-50% in space over other lossless image formats, such as PNG or GIF. That makes a big difference when you have a lot of data to preserve, or transmit.

There are tools to convert images to and from JBIG, I usually use one called cjpeg although there are others..