Digital BW, The Print

Hey Austin

You and I are in great agreement over everything but one. I believe such
discussions are MOST informative when people demonstrate what they are
speaking of. The only reason I kinda take Dan's side in this whole thing is
because all he's asking for is a presentation of evidence so that he can eat
his hat. I'd like to see the evidence too, not to see Dan eat his hat, but
to get into the whole "image dependant" thing. Everybody wants to say it's
image dependant, but nobody seems to give a hoot about what types of images
those are!

>> But how 'bout showing us some of your posterized images for our
>> edification?
> 
> Well, that is a problem.  You need to see prints, not web images...  Images
> can look fine on the screen, but when you print them, they are posterized.

So scan the prints.

>> It's most interesting when the same moves are made to a duplicate
>> 8-bit and
>> 16-bit file and the two are compared. If you remember my little article on
>> the topic
>> (<http://www.ourwebmaster.com/piezography3000/20020106ToddFlashner1.htm>),
>> which did use a BW image, fairly substantial moves can be made before
>> deterioration shows.
> 
> But that is VERY image dependant...

We both know it's all image dependent, but if nobody shows what types of
images handle abuse well and what types don't, we don't know what to make of
that knowledge... Other than walking on eggshells. And I believe that was
the point f Dan's challenge. The current conventional wisdom is that we all
need to walk on eggshells while doing any 8-bit manipulations, when in
reality some 99% of images do get 8-bit manipulations and do quite well by
them.

The other point is, if it's so damn difficult to demonstrate how the images
fail, the failure can't be as common or critical as we are led to believe.
 
>> Remember, we only need to retain a max of about 100
>> tones for a BW print; which means we can lose 156 out of 256.
> 
> Actually, no.  It depends on WHAT tones you "lose" and where they are.

Indeed. But think about it, some people get squirrelly if they see ANY gaps
in their histogram, when theoretically they only need to retain some 40% of
the tones, IF they are appropriately distributed.

I'm only trying to give people some freedom here. I bet at least 80% of the
people on this list do almost all their PS manipulations on 8-bit files, and
some minute percentage of those people get posterization in their prints
that ARE the result of inadequate bit depth. I bet of the percentage of
people who work their images exclusively in 16-bit have ALSO had a minute
occurrence of posterized prints. (see below)

>> It's not just if tones get lost,
>> it's how many, and where in the image, and what type of image.
> 
> Exactly!

The problem with most peoples experience in this matter is that one day they
work an image in 8-bits and they get a bad print. Another day they work a
different image in 16-bits and get a good print. They conclude working all
images in 16-bits is the fix. If they were to do side by side manipulations
to the same file, one in 8-bits and one in 16, they might just find the
16-bit file prints the same as the 8-bit.

I know I'm redundant in this, but not all image failures that are attributed
to inadequate bit depth are in fact that. Some of my scans, when I
manipulate them in a certain way, get harsh transitions between tones that
might appear to be posterization, BUT it happens the same in the 16-bit
variant. It is only through side by side comparisons that that phenomenon
reveals itself to be something other than "lost" tones.

Todd