Reading Paint Shop Pro image files (extension .psp) via libpsp supports the following:
Truecolor (24 bit), greyscale (8 bit) and indexed (8 bit = 256 color) images.
Layers including active layer setting and where possible linking too (GIMP layer linking is not - yet? - as advanced as that of Paint Shop Pro or Photoshop)
Transparency masks
Layer masks (called user masks in PSP) including disabling
Selections
Additional channels (alpha channels)
Layer blend modes if possible
Layer (in)visibility
Opacity
Transparency protection
Floating selections (with restrictions in old GIMP releases)
Resolution and Unit information