This program can convert a bitmap image to the C+4 multicolor FLI image. Sources and documentation are available on github.
the original (38694 colors)
160x256 MC FLI (98 colors)
160x256 MC FLI with dithering (101 colors)
160x256 MC FLI using 2x2 pixels (91 colors)
p4fliconv 305x245 interlaced HR FLI
with dithering
(237 colors, simulates 490 lines)