Background Image Low Resolution on 4K Display

[xcjs]

While using the viewer on Ubuntu 18.04 with a 4K display and a 200% scale, the background image appears to be the low resolution image.

It's possible that I could change this based on some of the error messages in the source, but I can't find options in the GUI to disable the background image or select a different/higher resolution copy of one.

[dafeder]

In the preferences change the visualization command to FAHViewer --background="/path/to/image.ppm"

Appears only ppm images supported.