Binary package “imgvtopgm” in ubuntu focal
PalmPilot/III Image Conversion utility
This program can convert, compress, and decompress up to 4-bit grayscale
images for displaying on the PalmPilot. It can take any pbm, pnm, pgm file
generated by the netpbm package and convert it into a suitable image
for the Pilot.
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Together with netpbm many image formats, including JPEG, PNG, GIF, TIFF
and BMP, could be converted into PDB format. This can be displayed on
PalmPilot/III by viewers like "ImageViewer", "TinyViewer" or "Spec".