Many years ago, the swedish National Land Survey issued topographical maps on CD-rom, using a self invented raster format known as RIK. Lately, these maps have been published as Open data. But this resurrected format is not known to FME.
There is open source code to read this format, and it is supported in GDAL. Thus, it can be read and displayed in Qgis but not (as far as I have found) read with FME.
What would it take to create a custom reader in FME using information in the links below? Apparently, the 'custom reader' ability in FME desktop needs a supported format to begin with.
https://sourceforge.net/projects/trikpanel/
https://github.com/OSGeo/gdal/tree/ab9e80368ef662712c963191fd86fde2c5b75600/gdal/frmts/rik