Photo books are getting more and more popular. But there is one problem: the file size of a self-created photo book can be enormous. For example if you have a 30-sided photo book with two pictures on every page and each picture has only 4 megapixels, the needed memory is already (30 * 2 * 12 MB), all in all 720 MB.
In order to reduce this amount of data, there is JPEG Compression. This function can be used to compress a single image layer by using the JEPG method. The resulting JPEG data will be attached to the layer (see also chapter 5.5 "Working With JPEG-Files"). If a document whose image layers have accompanied JPEG data is saved, the resulting file size is usually only a fraction of the normal file size.