by JimRaffel on November 23, 2005
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.
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by JimRaffel on November 11, 2005
In one form or another I am probably asked questions about dot gain being “bad” more than any other technical question. The short answer I have always given to this question is no, dot gain is not bad; but not knowing what your dot gain is can be very bad. Also, dot gain is no longer the correct term. Most industry experts now prefer the term Tone Value Increase (TVI). To find out more about this change, simply Google “Tone Value Increase.”
I am often asked “Shouldn’t my 25% tone swatch on the printed sheet read 25% if we are doing everything right?” No, because all the steps in the workflow prior to ink on paper have assumed some press TVI and adjusted for it. It is pretty much a mechanical certainty that the printing press will produce a larger dot on the substrate than appeared on the printing plate.
Because most design work is done based upon published industry norms like those found in GRACoL (www.GRACoL.org), it is critical to know the tone reproduction curve of your printing press on any given substrate. Unless your press is printing exactly to the published industry guidelines, you need to adjust the tone reproduction curve of the supplied work prior to submitting the job to press. Thanks to the miracle of CTP (and ColorMetrix) this has become a very easy task.
For example, the image above represents a common situation I am asked for assistance with. The red line on the chart represents the specified magenta printing condition as stated by the print buyer. Those of you who have been reading my e-mails for a while know that I refer to this as a specification which simply means we get paid (or not paid) based in part on achieving this condition. So, we have specified magenta TVI as follows; 25% – 14.72; 50% 17.82; and 75% 12.51.
Our own press finger print data (shown in blue on the chart) tells us that we are achieving the following actual magenta TVI conditions on our press; 25% – 16.20; 50% – 21.00; 75% – 13.22. The ColorMetrix graph shows us how much we need to cut back our curve and at which tint percentages in order to achieve the specified print condition for magenta.
Determining the exact numbers to enter into your CTP device in order to obtain this is a scientific exploit (one with some fudge factors and experience worked in for best results), I will be discussing in a webinar called “ColorMetrix and the cut-back curve.” The webinar will be conducted Thursday December 15th at
3:00pm Central time. The cost will be $89 for the 1-hour webinar, and a question and answer period to run until all questions have been answered. Attendance will be limited to facilitate answering all questions so visit our on-line store today to register.
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