From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 02/01/01-02:13:12 PM Z
FotoDave@aol.com wrote:
> But did you get posterization in highlights or shadows?
Posterization is throughout all tones and is unevenly distributed.
A lot of tones are typically "wasted" in the printed shadows to get a
threshold of densities. Most tones are placed in the mid range where
posteriztion is most noticeable. There just are not enough to fill the
printed highlights.
One should consider that a certain number of tones should be planned for
each Zone. Assume there are 13 Zones (0 through 12, range of a typical
palladium print). How many tones should be placed into each Zone
(theoretically for the moment as later the printer will have to produce
what is desired or be a limitation)? The number of tones should be that
number that, for that Zone, cannot be distinguished (by the eye) as
being steps (posterized).
The mid Zones will likely require the most number of tones. Ten tones
in Zone V can be seen as steps. How about 20? or 30? or 50? What is
the number? (This is where some research is needed.)
Then, what is the number for each of the other Zones?
Add the number of tones for all 13 Zones and that should indicate the
minimum amount of data bits required. But now there are two
limitations, the software and the printer. Both the software and the
printer need to be able to deliver the number of tones and further they
need to distribute the required number of tones into each Zone. Once
this is accomplished, the posterization will be at a fine enough level
that the result will be effectively continuous tone.
Why worry about posterization? Aside form producing steps in a
continuous tone (for example light on a curved surface), One
ramification is that for a certain photographed texture, a certain
difference in tonality is need to produce that texture. If the step
(caused by posterization) is great enough to be greater than that
produced by the texture, then the texture will effectively not be seen
(smoothed out). It is rather easy to smooth a surface or tone, but it
is incredibly difficult to create a matched texture. Of course one
could always claim they are painting with artistic license and leave it
at that, but one of the great challenges of photography is to re-create
in a print what one sees when looking at the subject.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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