Digital BW, The Print

As long as your operations are linear and you have maximal dynamic range 
there will be no difference between processing in 8 bits and processing 
in 16 bits and converting to 8.  That's pretty much covered in any 
textbook on signal processing, be it images (optical, IR or radar) or 
auido.

However, when you perform an significant nonlinear process or a series 
of nonlinear processes this may not be true. Applying curves - 
expecially "radical curves"  is a nonlinear process since it expands and 
dialates the range based on value. On images with long toes and/or 
shoulders this could be an issue. I could see where this type of 
processing would cause posterization on 8 bit images but not on 16 bit 
images.

Monitors are a pretty poor display device so it's not surprising it 
doesn't show up there. Prints are also viewed using reflected light and 
monitors are viewed using transmitted light. That probably also makes a 
difference.

Truman

Alessandro Pardi wrote:

> Jerry,
>
> I'm one of those you address, but my usual workflow is not what you 
> suggest:
> I *do* scan in 16 bits, actually I start with a raw scan from Vuescan. But
> afterwards, I convert to 8bits in PS and tweak happily away.
> Well, almost. Not being a fundamentalist, what I really do is open the raw
> scan, apply levels to set black and white point, and only after this first
> operation convert to 8 bits and start layering like crazy.
> Anyway, when I made a few tests applying the same 
> curves/levels/whatever to
> the original 16bit and a 8bit copy of some images (always starting from a
> 16bit scan, though), I was rigorous, and I saw no difference *on screen*.
> Now Austin makes me think I should redo these tests and print the two
> images, although they look the same on my monitor... Just out of 
> curiosity,
> what do you think is the reason behind posterization showing up only 
> on the
> print? The further curves you apply with partitioning workflows or some
> inherent difference between how monitors and printers render the image 
> data?
>
> Thanks,
> Alessandro Pardi