Does photoshop really use 15 bit?

Question

I have come across this answer https://photo.stackexchange.com/a/110776/78408

It says Adobe photosohp uses 15 bits thus Converts 16 bit images to 15 images.

Is it true? Why? Which versions are affects? Which photo editing software doesn't do that?

Answer 1

Yes, internally Photoshop converts 16 bit tiffs to 15 bits where 0:32768 is the same range as 0:255 in 8 bits.

Adobe's Chris Cox confirms it here: https://forums.adobe.com/thread/792212

And I have verified it by creating 16 bit tiffs in Matlab and examining how Photoshop reads the.

Note that Photoshop expands it back to 16 bits when saving tiff files by expanding it to 0:65535

Doing this has no significant effect on image quality and produces a shift of less than .01 Delta E. The math is simpler, faster and Photoshop dates back to the early 90's when CPUs needed every last help in speed.