(Toby Thain) writes:

I've tried. Their engineer insists that it's 30x faster to work with
15 bit quantities than 16 bit ones.

When your source data was probably from a 12-bit ADC, or maybe 14-bit,
working with 15 significant bits may indeed be completely adequate. And
there *are* advantages to using a representation that has some headroom
for "whiter than white" without overflow, and where the representation
for "1.0" is a power of 2.

But the couple of most recent comments in this thread are about the fact
that Photoshop's greyscale doesn't even seem to have 15 significant
bits, unlike the RGB representation.

Dave