Digital BW, The Print

David,

Well, here are some quick thoughts on your question before I dive into the
darkroom and develop my first Tech Pan roll from this year's Golden Trout
Workshop.  (And then have a Terminator marathon with my kids.)

The Photoshop Image Adjustment curves accomplish 2 things with these UT
curves in order to make a smooth and consistent grayscale image.  First,
they "partition" the gray inks.  Second, they evenly distribute a toner in
the amounts needed to make the various image tones, from the natural warm
gray base carbon pigment tone to a neutral or cool "silver print" look.

"Partitioning" the (warm) gray inks distributes them such that there is a
smooth, consistent grayscale "ramp" from the pure paper (0% ink) white to
the deepest (100% ink) black.  To do this only the lightest of the grayscale
inks is used in the highlights to avoid dots.  At the 100% black point the
black ink is poured in as heavily as the printer due and still have the
paper hold the ink without artifacts.  This gives the greatest dmax.

All the curves haves their ends at 0% and 100% ink (or 255 maximum luminance
white to 0, no luminance, black).

The toner ink, controlled by the image adjustment curves, controls whether
the image is, at the one side of the range, a warm, nature carbon-pigment
tone or, as more toner is added, a neutral or cool print. I use the warm
curve to make the "carbon on cotton" prints for old photo restorations.  My
favorite tone for landscapes is a neutral tone that looks just like my
lightly-selenium-toned silver prints.

The ink positions are not the same for hextone (such as the 1200, 1280 &
7500) and quad-tone (e.g., 1160 & 3000) printers.  (This difference is just
an unfortunate relic of being originally based on my 1160 PiezoBW system.)

The toner ink is in the "magenta" ink position in hextone printers and the
"yellow" position in quad-tone printers.

The lightest gray ink is in the "yellow" position in hextones and "magenta"
position in quadtones.

The cyan is the dark gray ink.  It is the same in hextone and quadtone
printers.  The cyan ink is the main gray that is most useful in adjusting
densities below the highlights.

Thinking graphically and in terms of complimentary colors is needed.

The input-output graph interfaces you with the printer jets.  I use the
8-bit light scale (0 = black, 255 = white) scale because the 256 steps are
needed.

The graph labels are the "complementary" colors (see the "color wheel" in a
Kodak/photographic reference, not a painting one).

Red controls the cyan, main gray ink.

Green controls the magenta-position ink.

Blue controls the yellow-position ink.

The points on the graphs are usually on or around the 5% steps of a 21-step
test file.  This makes it easier to relate the graph to the test file.

The gamma or 50% point was selected based on my readings of my PiezoBW
output on EAM.  I had an average 0.61 density at the 50% point on EAM as
read by my X-Rite densitometer/photospectrometer.

(Since my original variable-tone system was based on PiezoBW inks, I made
the systems as compatible as possible.  I wanted to be able to print the
same files with either system and have them be consistent in density.  The
inks of the systems are also somewhat consistent.  The cyan ink densities,
for example, are the same.  And, the cyan is the basic gray from which the
other grays are mixed.)

Using the Tab, & Control &/or Ctrl+Shift keys I navigate between graphical
points and raise or lower them as needed, using the numbers in the boxes.  I
use a densitometer and have a form that has the target information I need.
I record settings and changes, and save the curve with a new version number.
It's just an iterative process that can be picked up reasonably quickly if
one is comfortable with graphs.

Paul
http://www.PaulRoark.com
___________________________________



-----Original Message-----
From: David_J_Simons [mailto:dsimons@...]
Sent: Friday, July 18, 2003 9:35 AM
To: DigitalBlackandWhiteThePrint@yahoogroups.com
Subject: [Digital BW] Theory behind Ultra-tone Curves


I just ordered a CFS and Ultra-tone inks so that I can give them a
try on my Epson 1200.  It is awesome how Paul has put the effort in
to create us all curves for these inks.   How even it seems that one
may want to modify the curves to suit there own needs.   Are there
any good references on the theory be hind these curves that might
help me and other understand how they are arrived and how best to
modify them?

Thanks,

David




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