It's possible this exists somewhere else but I couldn't find it: something that can convert the BGI / Ethornell engine's sysgrp UI images to something you can work with. (target: senmomo). My searches brought me to xupefei's BGIKit, which had no binary releases, so I had to compile it myself (ok visual studio makes this easy actually). I'm not sure exactly what platforms these binaries will work on bar windows 64-bit, but at least you don't have to compile them yourself: https://drive.google.com/file/d/1cy1SnLSQZ_rCW8H6AsD9SZDxZrUd7qtZ/view?usp=sharing
Only the sysgrp tool is tested and only from game format to .bmp, have fun. To use that, call the program from the command line (cmd.exe or powershell) with the path to the file to be converted to bmp / from bmp as the sole argument, or more concretely:
SysgrpConverter.exe filenamehere