JimRaffel.com

Back in the dark ages of densitometry we utilized calculated values like Hue Error and Grayness to answer the above question. The reality we have been dealing with at ColorMetrix over the last several years is that spectral data will ultimately rule in our industry. While I do not expect press operators to start looking at spectral curves in making all their decisions, I can see some cases like the determination of yellow ink contamination that make a compelling case for purchasing instruments that are capable of displaying or collecting spectral curves.

While traveling last week, I was informed by a savvy technical associate from an ink manufacturer that looking at the spectral curve of the yellow ink on press is a very important part of most visits he makes to customer sites to assist in solving technical problems. The area of the curve to look at is from about 550 nanometers to 650 nanometers. If there is a dip in this part of the curve you are most likely dealing with a contaminated yellow.

I was able to create the image above, because our ProofPass.com solution now includes the ability to make single measurements utilizing an EyeOne. So the “Library Reading” (blue line) in the image above is an ideal yellow ink (uncontaminated draw down) and the “Sample Reading” (red line) is an actual press sheet. Notice the dip in the red line from about 540 nanometers to 660 nanometers. This show contamination of the Yellow ink and has of course changes the gamut vs. printing with the ideal yellow.

I also learned that this contamination is in part due to the changing formulation of inks. As printers demand higher and higher pigment loads in ink, the ink film thickness we put on the sheet becomes less and less. Well, with less ink film thickness it stands to reason that our lightest color ink is going to be more susceptible to contamination be it from other fountains of even from an excessively “dirty” sheet.

As always thanks for reading, and do not forget to look for us at the PIA/GATF Color Management Conference in Phoenix December 4-6 if you are attending.

*** Introduction ***

We will be in Las Vegas beginning Saturday for the 5th Annual ColorMetrix User’s Group Conference. The meeting runs through Tuesday, and we do not return until Wednesday, so there may not be a Golden Nugget next week. I am planning to try and use the www.JimRaffel.com site to post a daily update related to the User’s Group Conference, if you want to read about what we are up to. There is still time to register for our User’s Group Conference coming up August 21-23 at the Mirage Hotel in Las Vegas, NV. You will need to call us directly at 262-820-1131 to make all arrangements at this late date.

*** Jim Raffel’s Week 9 Golden Nugget…Press Characterization and Grey Balance ***

Back in my week 5 e-mail I mentioned how Eric Magnusson (www.leftdakota.com) mentioned that he is using a combination of L*a*b* values to arrive at tonal values (dot area) for ink jet proofs. This again, is because density which is used to calculate dot area is meant to be measured only on graphic arts ink sets. Well, as I began preparing my press fingerprinting piece for the User’s Group Conference, I decided to share some of my findings about improving press performance after a fingerprint (characterization) by utilizing grey balance techniques once included in our hexagon software product.

The techniques unfortunately depended upon density and thus only really work for tradition graphic arts CMYK ink sets. So I called the author of these formulas and found that he has also worked out a very reliable way to develop tone curves using L*a*b* like Eric’s method. While this is very promising, we need to test the math which will be happening in the coming months. Obviously we also need to test the outcome also. When all is said and done we should be able to offer a very easy and innovative way to create grey balanced curves for CTP devices.

Until then, however, I wanted to share the importance of adjusting grey balance as part of a press fingerprinting or characterization exercise. Here is the cheat sheet on how I go about it;

1. Output a set of linear plates.
2. Run the linear plates on press to standard densities.
3. Ensure that all other press variables are as they would be during a production run.
4. Double check the sheets for slurring doubling, etc.
5. Measure the sheets to confirm correct density, TVI, Trap, Print Contract, etc…values.
6. Use the “secret sauce” math in our hexagon program to create balanced grey cut back curves for your CTP device.
7. Output a new set of plates with the cut back curves.
8. At the same densities and TVI you should now have perfectly balanced color.

It sounds simple and while it is a bit more complicated than the above 8 steps make it sound, it is by no means rocket science. Want to know more? Join us a User’s Group (it’s not too late, really it’s not!).