In the main window, the user has two sets of scan options: Basic Options and Scanner Specific Options. The Basic Options tab contains the most common parameters that the SANE scanner backends provide, while the Scanner Specific Options tab contains all the options of the backend. The options listed here depend on SANE support for your driver: libksane (which the tool uses) should be able to display most of the types of parameters that SANE provides (analog gamma tables are not supported at this time).
The scanner specific options contains more detailed options of the backends. The tool does not have any special handling for these options.
If you are satisfied with your settings, you can use the little arrow on the top of the options splitter. When clicked it collapses or expands the options. The collapser can overlap the preview area, but fades away when the mouse cursor moves out of the collapser.