Digital BW, The Print

With digital files there is less info in shadows than highlights.

A quick disclaimer before adding the following information.  I was  
trying to remember where I heard this originally but was not able  
to.  Therefore, I add the following with the warning that if you want  
more detail on this you'll have to search for it.

 From what I understand, digital image files hold far less  
information in the shadows than the higher values.  This is due to  
the nature of the digital sensor's response (scanner or camera).   
Unlike the human eye or photographic film, the sensors record data  
according to a linear model.  So in the case of a 12 bit image, there  
would be 4096 different levels of luminosity.  But this doesn't  
translate to 4096 equivalent steps.  Instead, if we use an 11 zone  
model the amount of data recorded would be as recorded below, the  
data being halved for each zone. It's sort of like photographing 2048  
light bulbs, and turning off half of them for each photo.  With film  
this would result in single zone steps, from the highest zone to the  
least.  So, for a 12 bit image the amount of data per zone is as follows

zone        levels
1                2048
2                1024
3                  512
4                  256
5                  128
6                    64
7                    32
8                    16
9                      8
10                    4
11                    2

and for an 8 bit image

zone        levels
1                128
2                  64
3                  32
4                  16
5                    8
6                    4
7                    2
8                    1
...

Obviously, with the 8 bit image, if you try to open up your shadows  
at all, they'll posterize.  Whereas the 16 bit image will have a  
greater latitude for manipulation.

Well that is about the extent of my knowledge regarding this topic.   
An additional note however, is that this is the reason that you want  
to expose for your highlights and "develop" for the shadows with  
digital, the exact opposite of how one approaches exposure with film.

Hope that helps.

Eric
www.ericashworth.net