Digital BW, The Print

Derek,

I believe this discussion started with the question of whether there is
anything to be gained from converting 8 bit to 16 bit.  So, my comments are
in that context, and I believe there are significant advantages to such a
conversion if one is going to do any manipulation of the image.

>... whether the redistribution of the pixels is done by curves, 
> the contrast slider or other tool makes no difference. 
> If your adjustment causes a change which exceeds the amount 
> of headroom between each discrete tonal value then you 
> are going to reduce the number of independent tones in your image.

No question there. But it misses the 2 issue I wanted to point out.

First, if one starts with 8 bit and converts to 16 bit, there is, as you
later point out, enormous headroom.  This allows one to do significant
adjustments with no or virtually no loss of information -- if the right
tools are used.

Second, the "Brightness/Contrast" adjustment is different than the curves.
With the former I believe you slide the entire image scale up or down and
are much more likely to push things out the end, with a resulting loss of
information.  With the curves, you'll compress one side and stretch out the
other, with a much lower chance of losing information.  Again, this is in
the context of an 8 bit file that has been converted to 16 bit such that it
has headroom to absorb the compression without loss of information.

Paul
www.PaulRoark.com