geeky Piezography/Pictorico density data here

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Smieglitz@aol.com
Date: 05/29/01-10:38:56 PM Z

Y'all,

For anyone interested, here's some boring but perhaps useful data to some
from the Cone piezography quadtone inks printed onto Pictorico OHP run on an
Epson 1160 today (see below). Density was measured with an X-Rite 301
transmission densitometer. The fbf of the transparency (sprayed with Krylon)
was 0.03 and subtracted to get the net density values below. The net density
values of the Stauffer wedge were read through the OHP material.

The test image (reduced to 72dpi resolution for the web) can be seen at:
http://members.aol.com/kallitype/wedge052901.jpg

The original RGB file was converted to grayscale mode and then printed using
the Piezography Photoshop export plug-in @100% ink and Epson glossy paper
selected as the media. The lower half of the image shows a progression of
squares, each representing a 1% tonal change (i.e., % black fill) from 0% to
10%, 10% to 20%, etc. as the rows progress...0% to 100% overall. (All tones
are separated on my Mac monitor and on the printed transparency although they
may not show correctly on the web or with a PC.) The values for 10%, 20%,
30% tone, etc. on the right (end square of row) have printed between 0.02 and
0.07 density units lighter than the identical image tonal values on the left
(beginning square of next row), so the printer (or maybe my monitor) is not
consistent laterally.

I think I can tweak this well for gum printing, but don't see how I could get
a decent *digital negative* for printing VDB or Pt/Pd, etc., with this
system. A spectral neg from an Epson 600 was also run and its maximum
density came in at 0.22, roughly equivalent only to step 2 on the Stauffer
wedge. (An RGB negative using color inks was also run on the 600 and the
maximum density values are nearly double the piezography 1160 numbers
although riddled with artfacts such as dots & banding.)

Comments? Jeffrey?

I'm assuming since a typical gum bichromate layer for me only prints about
5-6 steps on the Stauffer wedge, that I have to adjust the 1160 output using
a curve that will incorporate all relevant image file data between % black
tones of 22% and 89% in Photoshop. This sound right or am I missing
something? Anyone know an easy way to correlate % black to the 256 levels in
Photoshop? Is it linear (1%=level 252.44, 2%=level 249.88, 50% =level 128.0,
etc.)?

Thanks for any insight. More tests to come although I won't bore you with
more numbers. I'll try to post some pictorial images resulting from the
tests.

Joe (smieglitz@aol.com) 

--
The first group of numbers is:
Stauffer step=net density=printed % tone on pictorico OHP matching net 
density of Stauffer wedge

01=0.08=22%
02=0.19=45%
03=0.34=64%
04=0.49=75%
05=0.63=82%
06=0.80=89%
07=0.95~92.5%
08=1.08=95%
09=1.23~95.5%
10=1.37~97%
11=1.51=99%
12=1.64~99.5
13=1.79=100%
14=1.94
15=2.09
16=2.23
17=2.39
18=2.52
19=2.64
20=2.78
21=2.89

This second set is:
printed % tone on Pictorico = net density

00%=0.00
02%=0.01
05%=0.02
07%=0.03
11%=0.04
14%=0.05
16%=0.06
19%=0.07
22%=0.08
24%=0.09
26%=0.10
28%=0.11
30%=0.12
33%=0.13
34%=0.14
37%=0.15
40%=0.16
41%=0.17
43%=0.18
45%=0.19
47%=0.20
48%=0.21
50%=0.22
51%=0.24
53%=0.25
54%=0.26
55%=0.27
56%=0.28
59%=0.30
61%=0.32
63%=0.33
64%=0.34
65%=0.35
67%=0.36
68%=0.38
69%=0.39
70%=0.40
71%=0.42
72%=0.44
73%=0.46
74%=0.47
75%=0.49
76%=0.50
77%=0.52
78%=0.53
79%=0.54
80%=0.57
81%=0.61
82%=0.63
83%=0.64
84%=0.66
85%=0.69
86%=0.73
87%=0.74
88%=0.79
89%=0.80
90%=0.85
91%=0.90
92%=0.93
93%=0.97
94%=1.02
95%=1.08
96%=1.27
97%=1.39
98%=1.49
99%=1.51
100%=1.77

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