"Actually, iirc, TGA format supports 16 bit greyscale?"

Hmm - now you come to mention it, I seem to remember that TGA (or another similarly-named) format supports 16-bit greyscale.

No use to me, alas. I don't have (AFAIK) any software that's capable of generating and/or manipulating 16-bit greyscale:-((

But Cheers, anyway,
Diolma