Re: Digital negatives

CHPalmer@aol.com
Wed, 17 Apr 1996 22:23:55 -0400

If you remember, a few weeks ago I sent a message about my work with digital
negatives for palladium printing. To recount briefly, I worked with Bill
Nordstrom and Rich Latour at EverColor to make negatives optimized for the
platinum/palladium process. I do my work with PhotoShop on a Mac; at
EverColor, the negatives are made on a Scitex ImageSetter with a 400 LPI
screen.

Randy Green (rgreen@musex.com) sent a note about his experiences printing
with very high line screen negatives, as opposed to the diffusion dither
method described by Dan Burkholder in his book. He was concerned that a 400
LPI screen (vs. 300 or 350) would not maintain the 256 shades of gray which
are possible in PostScript.

Within the confines of PhotoShop (as opposed to the software used by a
service bureau to run an ImageSetter), I am able only to test whether there
is separation in all 100 segments of the PhotoShop gray scale. If you will
recall, the PhotoShop densitometer reads from 0% to 100%. I have tested our
method by making a digital step tablet containing all 100 segments; to my
knowledge, there is no way within PhotoShop to create a scale with 256
segments. The SciTex maintains separation throughout all 100 steps of the
gray scale; I measured the density of all segments of the test negative with
a densitometer. On a more practical note, there is no trace of posterization
or loss of detail on visual inspection of either digital negatives or
palladium prints. So, if there is some compression of the PostScript gray
scale, I cannot detect it, at least in a way that would affect my work within
PhotoShop or the final quality of my palladium prints. If any of you have
further questions in this regard, you might contact Rich Latour
(RichLat@aol.com).

Well, here is the curve. You will notice that the extremities of the curve
are a bit steeper than the midportion. This is by design: it partially
compensates for the flattening in the toe and shoulder of the
platinum/palladium D/logE curve. It provides for considerably better
separation of tonal values in highlights and shadows than can be obtained
with the usual "analog" negative.

The table and graph will print correctly on your screen or printer only if
you use a font which has equal width for all characters and spaces, such as
one of the Courier fonts in either Windows or the Mac OS.

[-------------------------------------------------------------]
[ PhotoShop Density ]
[ of Original Positive ]
[ image: 0% 5% 10% 15% 20% 25% ]
[ ]
[ Density of Evercolor ]
[ Digital Negative: 1.99 1.86 1.75 1.56 1.42 1.33 ]
[-------------------------------------------------------------]
[ PhotoShop Density ]
[ of Original Positive ]
[ image: 30% 35% 40% 45% 50% 55% ]
[ ]
[ Density of Evercolor ]
[ Digital Negative: 1.26 1.16 1.08 .99 .93 .86 ]
[-------------------------------------------------------------]
[ PhotoShop Density ]
[ of Original Positive ]
[ image: 60% 65% 70% 75% 80% 85% ]
[ ]
[ Density of Evercolor ]
[ Digital Negative: .79 .72 .65 .56 .48 .40 ]
[-------------------------------------------------------------]
[ PhotoShop Density ]
[ of Original Positive ]
[ image: 90% 95% 100% ]
[ ]
[ Density of Evercolor ]
[ Digital Negative: .32 .19 .05 ]
[-------------------------------------------------------------]

O [-----------------------------------------------------]
p [ Digital negative optimized for palladium printing ]
t 2.00[o ]
i [ o ]
c [ o ]
a [ o ]
l [ o ]
1.75[ o ]
d [ o ]
e [ o ]
n [ o ]
s [ o ]
i 1.50[ o ]
t [ o ]
y [ o ]
[ o ]
o [ o ]
f 1.25[ o ]
[ o ]
E [ o ]
v [ o ]
e 1.00[ o ]
r [ o ]
C [ o ]
o [ o ]
l 0.75[ o ]
o [ o ]
r [ o ]
[ o ]
d [ o ]
i 0.50[ o ]
g [ o ]
i [ o ]
t [ o ]
a [ o ]
l 0.25[ o ]
[ o ]
n [ o ]
e [ o ]
g 0.00[ o]
a [-----------------------------------------------------]
t ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^
i 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
v
e ---------PhotoShop Density of Original Positive Image-------

Charlie Palmer
Albuquerque NM USA