«Verified Color Handbook: Using Color Process Control to Operate a Sustainable Printing Business in the New Economy Written by: Jim Raffel Provided ...»
Verified Color Handbook:
Using Color Process Control to
Operate a Sustainable Printing Business
in the New Economy
Provided Courtesy of:
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Content Provided by Jim Raffel under terms of
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Published in Sussex, WI (USA) by Jim Raffel Distributed by ColorMetrix Technologies, LLC PO Box 70 Sussex, WI 53089 http://ColorMetrix.com/ Verified Color Handbook | 2 Please Visit http://ColorMetrix.com/blog for Similar Content Introduction This eBook was produced by compiling blog posts written over a five year period at JimRaffel.com. I am slowly migrating printing industry relevant content to the Color Conversations blog on the ColorMetrix.com web-site. You may have received this eBook as a thank you for signing up for our ColorMetrix.com email list. First, thank you for trusting us with your personal information. We will never spam you and unsubscribing from the list is easy by following the links at the bottom of every email we send. Second, please enjoy this collection of what I consider the best printing industry relevant posts from JimRaffel.com.
This is a handbook of sorts but you won't find step by step instructions to operate your sustainable printing company in the new economy. You will find a collection of articles that will explain and explore the importance of color verification in achieving a sustainable state.
The first section contains articles about the technical aspects of color and color verification.
Sustainability in the printing industry requires that rock solid process controls be in place. Color verification and monitoring is the piece of the sustainability puzzle so many printers overlook. No other form of process control monitors overall process health in the plant and at the same time verifies the quality of the finished product for the customer.
The second section leads off with a piece on printing industry sustainability. The section wraps up with a piece about print not being dead, instead it's just changing. In between are several articles sharing my views and commentary on the printing industry. Most of these have been written in the last year or so.
I can also tell you that the industry stands a much better chance of remaining prosperous and successful if it pulls together with a sense of community. With that in mind ColorMetrix is building a user community where our customers can come and share technical tips and tricks as well as general information about the industry. In addition, we will contribute one seminar each month related to either new software releases of verified color in general. This community will only be available to customers with a valid technical support account.
Jim Raffel (8/23/2010) Verified Color Handbook | 3 Please Visit http://ColorMetrix.com/blog for Similar Content Table of Contents Introduction
Section 1: Color Verification and Process Control
1. Jim Raffel’s Tone Value Increase(TVI) notebook
2. Metamerism & Color Management
3. Metamerism: Hard copy vs Monitor
4. Make Proofs That Match Your Press
5. The difference between satin-gloss & high-gloss
6. Grey Balance & Printing like a Master
7. Proper Press Fingerprinting takes Commitment
Section 2: Printing Industry Sustainability and Business Issues
8. Sustainable Green Printing
9. Five Ways Color Process Control Impacts A Sustainability Initiative
10. Stop Printing and Start Communicating!
11. Color & The State of Printing Industry 2010
12. Feature Post: Printing (on paper) vs. Google
13. Printing is Not Dead or Even Dying
About ColorMetrix and Jim Raffel
ColorMetrix Technologies, LLC
Section 1: Color Verification and Process Control
1. Jim Raffel’s Tone Value Increase(TVI) notebook.
This chaperter was originally written as a five part series for the JimRaffel.com blog. I have rearranged and edited the parts to make what I now perceive as “better sense.” Density is king: TVI(a/k/a Dot Gain) is not measured it is calculated from density which is king. All the other values our modern densitometers display are simply calculated values from the densities the instrument measures. In short, all a densitometer does is transmit a predetermined amount of light and then measure how much comes back to the instrument. This is done through Red, Green and Blue filters so the instrument can tell if the light was stopped by Cyan, Magenta, or Yellow ink.
One reader made a comment at JimRaffel.com that density is also a good indicator of ink film thickness on a printing press. Just remember that two inks with different pigment loads can record the same density and have different ink film thickness.
TVI really is a better term than Dot Gain: My short answer for this is that a densitometer (or spectrophotometer acting as a densitometer) does not actually measure dots, so how can we really call it Dot Gain? Add to this the fact that some systems being used for proofing result in continuous tone images with no dots and my position becomes a bit clearer. Those on the SWOP committee that spearheaded the initiative to change this misleading term (which I resisted early one) should be commended. After all, when a 50% patch of a color increases to an apparent 65% patch of that color the tone value has in fact increased regardless of whether that patch is made up of dots or not.
TVI in and of itself is not a bad thing: Back when TVI was called Dot Gain, I remember going into print shops and having pressman tell me “No, we don’t have any dot gain.” This was not ignorance (they knew they did), but instead a misconceived notion that TVI was a bad thing. I always countered this by saying that Dot Gain is not bad; however, NOT knowing what you Dot Gain is, is a bad thing.
Think of it as trying to get from one city to another in a car without a map. We need to know where we are in order to get where we are going.
(Note: this paragraph was originally written in early 2006) GRACoL 7 appears to be taking our pressrooms in a direction where TVI will be significantly less importance in monitoring production run stability. Instead GRACoL 7 is based on maintaining gray balance utilizing density and L*a*b* values. Over all, I feel this is the right direction to go and from what I have heard and seen several test press runs have proven this to date. Even GRACoL 7, however, recommends taking a look at CMYK TVI values when the system does not seem to be working as intended. TVI and TVI variation are still incredibly powerful and simple measures of press stability. I have watched real pressroom experts track down loose blankets and other press problems by first taking a look at TVI numbers, then looking for the actual mechanical problems. (NOTE: If you have not read the GRACoL 7 draft quite frankly you must. This methodology will become a barrier to entry very quickly.) Verified Color Handbook | 5 Please Visit http://ColorMetrix.com/blog for Similar Content Measuring TVI on Inkjet proofs is Meaningless: I considered changing this topic, because the title is a bit inflammatory. Understand that my frame of reference is users of our software who rely upon density and TVI as process control measurements for inkjet proof production.
Far too many times I have seen the density and TVI values stay within tolerance, and yet the Delta E shifts can be huge. The graph above shows the spectral response of the Red, Green, Blue, and Visual filters used in graphic arts densitometry. Those filter responses are specifically designed to address the spectral response of process cyan, magenta, yellow and black. One would be wise to compare the spectral response of the inkjet inks your proofs are made with to that of the graphic arts inks being utilized in the pressroom.
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2. Metamerism & Color Management In response to the blog post “Golden Nugget #15 Which Instrument Should I Use?” on JimRaffel.com,
Adam made the following comment:
“This is because some spectrophotometers are built with spectral response every 20 nanometers while others respond every 10 nanometers.” I believe this is referred to as the resolution on the device.
Adam’s comments got me thinking about the visual spectrum in general and all the different ways we work with the spectrum on an everyday basis in our industry.
So, for our discussion Metamerism is...
When two color samples appear to match under a particular light source, and then do not match under a different light source, this is an example of "sample metamerism." One can conclude that the spectral reflectance distributions of the 2 samples differ, and their plotted reflectance curves cross in at least 2 regions.
The next image shows 3 examples of the GATF/RHEM Light Indicator which is printed with two magenta colorants which are a metameric pair. In this case when viewed under proper graphic arts lighting (5000K), the two colorants appear the same color. When viewed under other light sources you can see the two different colorants.
Verified Color Handbook | 7 Please Visit http://ColorMetrix.com/blog for Similar Content The RHEM indicator is a great tool, because it comes in rolls with self adhesive backing, so one can purchase them from GATF, and attach them to color proofs going out to a customer. If the customer is complaining about color a simple question about the appearance of the indicator will let you know if they are viewing the proof in 5000K lighting.
This brings me to the fun part of this week’s conversation. I happen to know the “Adam” who commented on last week’s Golden Nugget, and he is a graduate student at RIT. Adam and I had an interesting discussion yesterday about Color Management being the solution to the metamerism that exists between ink jet proofing ink and media combinations, and pressroom ink and paper combinations.
Color Management also solves the problem of soft proofing metamerism that exists because of the way displays (CRT or LCD) are illuminated. Without Color Management there would be virtually no way to match ink jet or soft proofing devices to ink on paper printing presses. Because these colorants are metameric it is increasingly important that all viewing of color occur under proper 5000K lighting.
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3. Metamerism: Hard copy vs Monitor Definitions: First, metamerism requires a pair of objects. The two objects are often referred to as a metameric pair. In order to be considered metameric the pair must; match under at least one combination of illuminant and observer; not match under at least one combination of illuminant and observer; and have different spectral response curves.
Metramerism Tests: The previous chapter shows an example of the GATF REHM indicator used for visual assessment of light sources. This is also an excellent of example of a visual test for metamerism. The two samples may also be measured by a spectrophotometer, and then an instrument test for metamerism can be performed. If the two samples exhibit a small Delta E under one illuminant observer combination, but have different spectral curves that cross at least three (3) times they are metameric.
Our ProofPass.com system was recently used to measure two samples. Below I have provided the L*C*h* values of a 'Red' swatch measured on a hard copy proof and then reproduced and measured on an LCD monitor.
Hard copy Monitor L* 40.56 43.02 C* 60.85 61.31 h* 28.44 27.9 The CMC(2:1) Delta E of the above two samples is 1.34 in a D50/2 degree environment.
Now, take a look at the spectral reflectance and emission curves of the two swatches. (Library Reading = Hard copy and Sample Reading = Monitor) Again the instrument test for metamerism states that if the spectral curves differ, and cross each other at least three times, then the objects are metameric. The curves look different and I count at least 10 crosses.
As long as the physical sample is viewed in a proper viewing booth, and the monitor continues to be calibrated and also viewed in proper conditions, the metamerism effects of hard copy vs. monitor proofing above should not be a problem. My concerns about this type of metamerism extend to placing a package on a retail shelf which is seldom a D50/2 degree environment.
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4. Make Proofs That Match Your Press It does not matter if you are utilizing a methodology like GRACoL G7, or a more traditional color management approach. In either case you will include a target on each print job with the same color bar swatches that you output on the proof. This will allow you to measure the press OK sheets and compare them to the proofs, thus building even a larger statistical database to call upon.
When utilizing software like ColorMetrix and ProofPass.com products for process control and print certification purposes it does not matter if you are using a methodology like G7 or traditional color management. While there are some new formulas out there to run the collected data through the tried and true colorimetric data (L*a*b* and derivatives along with some version of Delta E), do a great job comparing two similar or dissimilar imaging systems.
Unlike density and dot gain values which must be used with pigment sets designed for 4/color process printing, L*a*b* values allow the comparison of an inkjet proof and an offset press sheet. This is possible because we are looking at the actual colors, not values derived from a formula which assumes a certain pigment set.