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Re: Digital Negatives with enough Tones for Pt/Pd

Carl Fransman wrote:
> Jeffrey, the densities add, but you don't get more tones since at a given
> point, you simply add up three densities.

Ah, but that is just what happens.  The reason that I get more
individual tones is because I have done three scans covering the
respective (low-mid, high, highest) regions.  Ideally this would produce
256 tones from the low-mid negative, another 256 tones from the high
negative, and another 256 tones from the highest negative.  The actual
number on tones is less for various reasons, but still significantly
more than 256 (the maximum possible from a single scan.

You point about the 8-bit printer is of concern as well and should be
remedied by the use of the three negatives as well.  Remember each
negative deals only with a specified portion of the original negative
unique from the others.

> If you do multiple exposures,
> you can get more tones by varying the exposure as I've explained in
> another mail. This then gives you 256 grayish tones + 256 black tones (ie
> in the case of a duotone).

Sorry, but I do not see this happening when only one scan is used.  Even
with a 12-bit scanner the information is converted to 8-bit and used
that way in Photoshop.  In the duotone scenario you describe here, each
of the 256 grayish tones are simply combined (added or whatever) to the
corresponding black tone at that same location on the image.  The result
is a total of 256 unique tones, although each tone may now be different.

Look what happens for a single pixel of the image.  In a duotone, a
level 1 color is assigned and a level 2 color is assigned to that
pixel.  However, every pixel that has that identical level 1 color will
also have the same level 2 color applied.  The result is that wherever
in the image a certain black tone of the 256 possibilities is located,
the same grayish tone will always be assigned.  The net result being a
total of 256 unique tones.  This same process occurs in RGB and CMYK
modes as well, the result is a total of at most 256 unique tones.

I could be wrong and if so, please explain in detail how it is you get
more tones and how to count them.  I have counted the tones produced
from a 256 step gradient and have not been able to get more than 256.

And thanks for the info that printers are 8-bit, because if Photoshop
ever did get more pixel depth, I would need a new printer and/or
driver.  The printer being 8-bit definitely means that multiple
negatives will be needed to generate more than 256 tone in the print. 
It does not mater much if the negatives are made to print one at a time
with multiple exposure or all at once with one exposure.  (Note that the
negatives must be made specific to the way they will be printed.)  I
have my own preferences for the sandwich.  What does matter is that
several scans must be made on separate ranges of the original negative
in order to transfer a larger number of unique tones to the print.

-- 
Jeffrey D. Mathias
http://home.att.net/~jeffrey.d.mathias/