8bit Images in 16bit Mode

[diffid]

There are a few mentions in the tutorials on this excellent website about working in 16bit mode even for 8 bit images.

With regard to Photoshop or After Effects, putting 8bit images into a 16bit project appears to allow far better manipulation of the 8bit image.

Is this all to do with higher precision calculations, as the 8 bit image still only has 256 levels to work with.

Or does Photoshop do something else, like throw in some very discrete gaussian noise to each channel to spread the values out into a wider range of levels available in a 16bit format.

I read somewhere that from Photoshop 5, when 16bit mode was introduced that it was 15bit image + 1 bit noise, whatever that means. :-)

Thanks

[Colin Southern]

Is this all to do with higher precision calculations, as the 8 bit image still only has 256 levels to work with.

Yes

Or does Photoshop do something else, like throw in some very discrete gaussian noise to each channel to spread the values out into a wider range of levels available in a 16bit format.

Not that I'm aware of.

I read somewhere that from Photoshop 5, when 16bit mode was introduced that it was 15bit image + 1 bit noise, whatever that means. :-)

They simply use a 15 bit representation - the other bit isn't "noise", it's just not used (in a 16 bit word). I don't know the exact reason, but one reason offered (by one of the Adobe "insiders") is that when 15 bit representation is used you then have an unambiguous zero point, which is important for many areas, including blending modes.

[diffid]

Ok, great thank you.