For XIF files, Pagis typically scans the TEXT layer as 300 dpi Line art. This size is for printing, which has higher requirements than the video monitor screen. This picture layer in XIF files is compressed with JPG compression, which is optimum for continuous tone images, like photographic pictures. However, JPG is far from optimum for text, the dark smudgy artifacts surrounding sharp edges are exceptionally bad. Therefore, the XIF text layer is seperated and scanned and stored as Line art, and that layer is NOT JPG compressed, and so is not affected by the JPG artifacts.
Line art compresses very well via other methods.
Pagis does not require that you use XIF files. It will handle most other file format choices, but XIF is a strong choice for storing documents compactly. I would suggest XIF for documents , but concerning your regular photo scans, you should know that XIF images are JPG compressed. Repeating, use of XIF is optional, but is ideal for documents. But a file is not even required, you can scan directly from Pagis into your own photo editor if desired.