FITS (Flexible Image Transport System) is a popular open standard for storage, transmission and processing of digital data. For the details, one is referred to the corresponding Wikipedia article. This page allows you to configure presentation and processing of FITS data in KStars.
The left panel is for configuring FITS viewer itself.
Check the Use FITS Viewer item if you want automatically display received images in the FITS Viewer.
The Single Preview Tab item is to display all captured FITS images in a single tab instead of multiple tabs per image. The Single Window Capture item is to display captured FITS images from all cameras in a single FITS Viewer window instead of a dedicated window to each camera. The Single Window Open item is to display opened FITS images in a single FITS Viewer window instead of a dedicated window to each file and the Independent Window item is to make FITS Viewer window independent from KStars.
The right panel lists processing options. The Auto Stretch item is to always apply auto stretch to images in FITS Viewer, Limited Resources Mode is to enable limited resource mode to turn off any resource-intensive operations, namely: Auto Debayer (bayered images will not be debayered; only grayscale images are shown), Auto WCS (World Coordinate System data will not be processed; WCS maps sky coordinates to image coordinates; equatorial grid lines, object identification, and telescope slew within an image are disabled), and 3D Cube (RGB images will not be processed; only grayscale images are shown). You can switch off some of these resource-greedy operations separately as well.