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.
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.
This week as part of a larger conversation a potential client asked, “What should my color bar look like?” My first thought was that it would be easier to answer the following question…”What is the meaning of life?” The answer to the color bar question can be both simple and complex, at the same time. We should begin with why this potential client was asking the question. The company involved is a very large consumer products concern. As such they are the ultimate consumer of the print (i.e. - they pay for it). Others in the supply chain are pushing for a fairly large color bar to be included on each package. While in principle I agree with measuring as much as you can, I have also assisted customers with almost not space for a color bar and found a way to measure enough to be meaningful.
The interesting trend I see in consumer product printing (i.e. - packaging) is towards more informative color bars. While in the past getting designers to allow even solid blocks of the process and spot colors was like pulling teeth, now you see targets approaching the size of the ECI target (sarcasm). I believe the reason for this is simple. Managing libraries of dozens, hundred, or even thousands of spot colors can be almost impossible. If, however, one moves towards some form of 6 or 7 color process printing some pretty amazing economies of scale begin to occur.
The trick is that if you are producing a critical spot color with some build of process inks those inks and all associated print attributes need to be “spot on.” The only way I know to control critical press factors like density, dot gain, print contract, etc… is to measure as many color bar patches as possible. See how simple the answer to these complex questions can be?
So, ranked in order of importance (Jim Raffel’s order) here are the patches I would want to see on a press color bar. (We can talk about proof control bars in another Golden Nugget)
- Unprinted substrate patch (to zero out substrate when necessary)
- Solid patch for each process (and spot) color (needed for solid ink density (SID))
- 3/Color Grey patches at multiple tone values (if you are not sure why please re-read all your Golden Nuggets before proceeding)
- Mid-tone patch for each process color (only way I know to gather dot gain (TVI) values)
- Process color over prints (needed to measure trapping efficiency of inks, this gets a bit tricky in 6 and 7 color printing)
- Additional highlight and shadow tone patches of each process color (i.e. - we need a 75% patch to calculate print contrast)
- GATF Star targets or microline targets (used to visually evaluate for press slur and doubling issues)
All of the 7 items listed above are important and truly necessary but if space is an issue start with number 7 and work backwards removing items until the bar fits. Also, items 3 and 4 could be easily reversed; having one without the other makes diagnosis of grey balance issues difficult at best. Now, for my radical comment of the week….if you do not have room for items 1-3 and quality print is important to you…redesign the piece.
