Digital BW, The Print

Folks,

here is the beginning of a bit of research on my part to track the performance 
of my 1160  with piezo inks and v.5.1.2 plug in.  Depending on your level of 
tolerance for tech talk, you may want to read  the details below. But the short 
story (and partial conclusion) is this:

Digital printing, especially a profiled, "canned" solution like piezoBW, 
promises to allow "print-on-demand". This means you can expect to make the 
identical print a week, a month or a year later. For this to happen, however, as 
we all know too well, the hardware (including heads, inks, CIS tubes etc) has 
to operate identically over time. A lot of us have developed  voodoo methods 
for fighting the inconsistencies of the system and often, but not always, these 
work. Even so, unless things get really out of whack, we cannot be sure that 
print-on-demand is a realistic expectation. We tend to count on eyeballing and 
the promise of the accuracy of canned profiles.

What I haven't done methodically for myself until now is set a standard for 
what is the ideal out-of-the-box initial state of the system and when and how it 
drifts. Here is what brought this about:

My printer sat for a period of 3 months unused. The first prints I made had 
extremely flat 3/4 tones. This went on for days. A few weeks later, it all seems 
to be back to normal. But how "normal" is normal is the question. Considering 
the accuracy promised by profiles, the degree of "device drifting" over time 
may simply overpower the accuracy promised by any profile. And I certainly 
wasn't smart enough to start taking readings when I first installed the whole 
thing a year ago. So I really don't know what an ideal standard is. I wish 
ConeTech would make available a list of ideal densities for their gray scale.

So, my first conclusion and proposal is that anyone using piezo - and other 
multitone gray ink systems - keep track of their grayscale performance and 
compare samples over time. The system may drift  in ways your eyes may not 
always notice. 

The second issue this raises is how to go about measuring. A simple bw 
densitometer is a good method. But this time, I went the colorimeter way 
because I wanted to track both density and color over time. This time my 
samples are limited to only 3. But I am publicizing these results for general 
comments and to see if and how they may be useful to this community.

Now for the tech talk....

The set up:
I used prints of the same grayscale file made on the same batch of Orwell 
paper  with the same Orwell profile, using the same software. These were 
made on 5/10, 11/26 and 12/13 of this year. They were kept in the dark in 
average temp/humidity conditions.  During this period, the inks have been 
refilled by pouring new inks into partially empty CIS bottles while making sure 
no air enters the system. All inks came from fresh, sealed Conetech bottles.  It 
is important to keep in mind that just before the 11/26 tests were printed,  the 
printer sat idle for about 10 weeks. 

The method:
I used an X-Rite DTP22 (Digital Swatchbook) and saved all readings in 
Colorshop 2.6. From there I exported relevant data for graphing. 
I made 3 such graphs:

- One is similar to what a simple densitometer would have recorded. Took 
readings from paper white (marked p on the scale ) to 100% black in 10% 
increments.       
>>>>>file:  visDensORW.JPG 

- The second takes colorimetric data into account and plots deltaE deviation of 
the 11/26 and 12/13 scales when compared to the 5/10 scale. This is the one 
that shows the wildest results. For this to be meaningful, we have to take into 
account the time between printing an reading. All scales were read at the 
same time, making the 12/13 the "freshest" print. So, this result may show us 
how prints "cure" - even in the dark - above and beyond hardware system drift.
 >>>>file:  dE-ORW.JPG 

- I made one more graph, partly out of curiosity and partly to throw it out there 
and see what everyone's take is: I plotted the Hue values of the HSB numbers 
for each reading. The best way to see what this means is to go to Photoshop, 
click on the color picker at the botom of the tool palette and play with the 
settings of the vertical color bar that defines the Hue position for the current 
color. You will notice that you go pretty much from red, through yellow and into 
green territory. The reason, of course that these colors don't jump out at us is 
that the saturation (the S in HSB) is low in the "gray" inks. But the Hue position 
may be an indicator of a cast and of a drift in that cast. As for the B 
(Brightness), that simply tracks the density values and is covered in the first 
curve. This curve proposes a way to look into the color of the grays.
>>>file: HSBcompare.JPG 

I have uploaded all three in the Files of the group. You can follow the link 
below (make sure to copy and paste rather than just click):
http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/files/Message%
20Related%20Files/12_2001%20uploads/Orwell%20scales%20over%20tim
e/

If you get lost with the link, simply look in the Message Related Files folder for 
December.

Food for thought I hope. Your comments will be most welcome.

Thanks,

Antonis