"Monica Schulz" wrote in message
...
Maybe I did not make myself clear enough in my last post.
What I mean
is that there is no need for such a wide variaty of paper
grades in
color printing as there is in b&w because contrast can´t be
manipulated that much in color as in b&w. I came thinking
about that
after reading another old thread so I will use the important
words of
the relevant post.
To adjust contrast means to make the image brighter or
darker. The
only way to do that is to make the dyes thinner. This lets
more light
reflect off the paper. But as a dye gets, say, thinner it
removes less
of its anti-color until it finally disappears and no
anti-color is
removed. And the other way around if the dye gets thicker.
So the
scale doesn´t go from, say, a dark magenta to a light
magenta but from
dark magenta to white. Or from a saturated magenta to an
unsaturated
magenta.
The digital process can compensate for this unwanted
increase or
decrease in saturation if contrast is adjusted in the
luminosity
channel of lab-mode. In this case neither hue nor saturation
is beeing
changed. There is a nice little example of that on
http://www.cambridgeincolour.com/tut...hop-curves.htm.
But
we can´t do the same in analog color printing.
It could well be that this is complete garbage as far as the
subtractive mixing of the analog process is concerned and if
so I´d be
happy if someone tells me so that I can get this idea out of
my head
and can think in another direction.

Best regards!
Monica Schulz


Something very like the "curves" effect can be done in
chemical photography be means of elaborate masking and by
using such techniques as coltrolled flashing. Both
techniques were widely used in making the plates for
four-color printing. However, its very much easier to do it
in Photoshop and one can see immediately the results. Most
of the tailoring done in Photoshop can be done in analogue
photography but can be very complex to do there.
Contrast and brightness are different. This is
especially true of most reproduction media where the maximum
brightness is determined by illumination. What adjusting
contrast does is to fix the points that are the minimum and
maximum brightness of the image. As contrast is increased
something must be lost. That is where the "brightness"
adjustment comes in. That controlls what is to be the
midpoint of the gray scale. Its possible to extend the range
of tones that will reproduce without falling off one end or
the other by shaping the transfer curve and that is what
Photoshop is doing. Many films and papers have curves which
affect the reproduction of gray tones because they are not
straight lines. Similar curves are available in color films
and papers. This one of the things that determines the
difference between "portrait" material and commercial
material. The overall conrast may be the same but the
placement of reproduced tones in relation to the originals
is different.


--
---
Richard Knoppow
Los Angeles, CA, USA