Piezo consistency: Colorimetric data over time.
2001-12-15 by antonisphoto
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