Digital BW, The Print

Well, Levels *is* just a handy interface for a Curve Adjustment... to 
really start filling things in I think you have to introduce 
something that does a little averaging... curves just scale your 
values as-is... so every 159 level gray, for instance, is going to be 
multiplied by the same value via the curve, but in a convolving 
filter it will depend on the adjoining pixels and thus introduce 
variation and kind of fill things in.

Actually, I don't always like setting my B&W points first in PS 
because it clips your data right there in that one step and then if 
you do more out of range adjustments you get even more clipping... 
too bad PS can't maintain the out of range data...  If I have to, I 
will usually expand the data a bit, but not right to true b&w pts, do 
other stuff and then do a final b&w pt setting (if I haven't done it 
already using curve adjustments) as a last step.

64 bits per channel is way over-kill, but it is just a default in my 
program which could be changed... the real thing is that my own 
program is more a learning tool for me than anything else.  When I 
got started in digital image editing with PS 3 years ago it was all 
too baffling to me and the tripe that is written in most PS for 
Photographers-like books just shows you what buttons and sliders to 
use.  I never felt I got a good enough grasp of what I was actually 
doing from just the smoke and mirrors explainations in these books to 
do it intelligently... but I found that after I went through the 
effort to write and de-bug my own code, for something like an unsharp 
mask routines etc. that I then *knew* pixel for pixel exactly what I 
was doing and why, even when it was hidden "under the hood" in PS... 
just my mentality and my method... probably not shared by many others 
on the list:)

mark

...
> Mark,
> 
> I think that 256 shades of gray are probably more than adequate for 
B&W
> printing but as you note, adjusting an 8-bit file causes that 
number to
> drop. Fortunately we can actually lose quite a bit and still come 
up with a
> good print. I suspect that as few as 100 shades of gray may be 
acceptable in
> some images but it is very easy to fall below an acceptable 
threshold if you
> are not careful.
> 
> With the 65,536 shades of gray available in a 16-bit file the 
chances of
> having it visually degrade during Photoshop adjustments is greatly 
reduced
> to say the least. Although I imagine if you try hard enough you 
will still
> get things out of whack!
> 
> At 64 bit or 18,446,744,073,709,551,616 shades of gray you are 
probably way
> beyond what is needed. In all honesty I wonder if we couldn't do 
just fine
> with say 12-bit or 4096 shades of gray. In any case you don't need 
more that
> your scanner or digital camera can output and this has been in the 
10 to
> 14-bit range.
> 
> It is interesting to note that even when you scan 10 to 14-bit data 
to a
> 16-bit file you can lose image data if you do not spread that data 
over the
> full 16-bit range before you start applying gamma or curve 
adjustments. In
> other words you need to set your black and white points in levels 
first and
> seperately before any other adjustments.
> 
> Martin Wesley
> http://www.carolyn.cc/Guests/MartinWesley/pages/MW_01.html
> http://www.borderless-photos.de/guests.html