Archive for the 'viewing conditions' Category

#67 Metamerism: Hard copy vs Monitor

Published
by
Jim Raffel
on January 16, 2008
in GATF, RHEM indicator, calibration, color, delta E, illuminants, matamerism, measurement, monitors and viewing conditions
. 4 Comments

The most visited post on JimRaffel.com in 2007 is #16 written October 2005 and addressing metamerism. Because of the popularity of this post I have decided to revisit the topic. I will start with some basic terminology and definitions. Then, I am going to present a real world example we are dealing with right now at ColorMetrix.

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: Post #16 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)

graph_spectralphp.png

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.

Golden Nugget #11 Press Run Analysis / Print ’05 Information

Published
by
Jim Raffel
on September 22, 2005
in Print 05, uncategorized and viewing conditions
. 0 Comments

Golden Nugget #11 Viewing Booths

While at the show I decided it was time to begin acquiring tools and technology for our new inkjet proofing test site. We have reached a point where we need to be able to simulate customer proofing situations on our office. As time goes on the complete set-up will include; an Epson 4800, AbsoluteProof RIP, Gretagmacbeth ProfileMaker, GTI light booth, and various color viewing tools from Beta Industries.

While acquiring our new light booth from GTI, I learned why the newer (and might I add a great deal more expensive) generation of light booths have a light source which can be dimmed. When I had almost completed my purchase, a friend stopped to say hello, and said “oh great you are getting a new light booth, you did get the dimmable version right?” OK, to say the least this friend is not subtle in letting me know if I did not get the dimmable version I was basically and idiot.

Not wanting to remain an idiot on this subject I asked the classic dumb question (I know there is no such thing as a dumb question, except one which goes un-asked), why do I need a dimmable light booth? I am sure more than 50% of my readers know the answer to this question, but as person who has been focuses on the hard copy proofing market for the last several years I did not. The answer is that if you are doing any form of monitor proofing and want to compare the monitor results to hard copy, you must be able to dim the light booth to match the white point of your CALIBRATED monitor.

Then, Bob from GTI showed me an example of this using an ICS soft proof, and a press sheet. He started with the booth at full intensity. The two did not appear to visually match. He then dimmed the booth to match the white point of the monitor, and basically it was now a perfect match.

Matching the white point is pretty easy too, even on the lower end model we have with just a knob to do the dimming. Simply bring up a white background on your monitor, and then put a blank piece of the paper you are proofing or printing in the light booth. Put the two next too each other and dim until the whites match.

In short, spend the extra money if you ever even think you might want to compare virtual proofs to hard copy proofs or press sheets in a light booth.

Golden Nugget #4…Proper Color Viewing Conditions

Published
by
Jim Raffel
on July 9, 2005
in viewing conditions
. 0 Comments

Once again this week our topic has been set by a golden nuggets reader. I will get to that in a moment, but first I wanted to share some observations I made this 4th of July weekend. I had the honor and pleasure of joining my son’s Boy Scout troop for their last day and half of summer camp. Now, you may be asking yourself what this could have to do with the printing industry. Well, it showed me that print is not dead or dying as many a naysayer has been predicting for a long time.

It also showed me once again why I got into this great industry. At Boy Scout camp (at least at our Boy Scout camp) no electronics are allowed. What is allowed are books, Magic cards (a game based on decks of trading cards that some one had to print!), Scout Books, merit badge books, a Wall Street Journal (yes, that was mine not the boys) etc…. I think you get the idea, lots of printed materials. I watched a group of 20 boys (sorry, young men really), keep themselves busy for 4 hours with several decks of Magic cards, and a tournament they set-up and scored on a piece of paper. For those of you with children; that’s right no Xbox, Game cube, TV, or other electronic gadgets, just good old fashioned print.

I also was reminded of the purpose of that first printing press…the archiving and sharing of human knowledge for the ages and most importantly the masses. When I had a little downtime, I was flipping through my son’s Boy Scout book. I was quite honestly amazed at the wealth of knowledge contained in that relatively small book. All I can say is that if I ever get lost in the wilderness that is the one book I would want with me. All of us just need to keep searching for the niche’s we can serve better and longer than any other media.

*** Jim Raffel’s Week 4 Golden Nugget ***

I have a friend (let’s call him Doug) who is a technical sales representative for one of the few remaining national distributors left in our industry. Doug works out on the West coast, and specializes in the Flexographic part of our industry. Doug has also been using ColorMetrix for several years now to successfully fingerprint dozens of flexo presses up and down the west coast as the plates are converted from analog to digital (CTP).

Well, Doug called me last week with a question I thought would benefit all of us. He was in the final stages of a CTP conversion. The re-curved plates were on press and he had achieved the correct densities and dot gains that his many years of experience told him should be resulting in a nearly perfect print. Doug, however, was looking at a balanced quarter tone grey (25/18/18) and it was looking a little red press side. Doug told me that when he took the sheet outside in the natural southern California sunshine (this probably will not work in the mid-west at 5pm in the month of December), the grey looked prefect.

My first question to Doug…what kind of light booth does the customer have press side. Doug’s answer…”a home made one.” Wrong answer! The light booth had no sides to keep out ambient press room light, and Doug could not confirm that the bulbs even met the 5000K standard. The human eye is perhaps the best judge of color in the world, but only in proper viewing conditions. I reminded Doug that his employer sells at least two brands of light booths that I know of (http://www.gretagmacbeth.com and http://www.gtilite.com) and suggested it was time his customer purchase a proper press side light booth.

I am of course quite certain everyone else reading this has a proper light booth press side. If by some chance you do not…it really is time to call your dealer sales person, and at least have them provide you the information you need to make an informed decision about why you will run jobs worth tens of thousands of dollars on a press worth millions, but you won’t spend 5 grand (or less) for a decent light booth.

*** 2005 ColorMetrix User’s Goup Conference Info ***

Remember, we will be picking a selection of these topics to discuss at the 5th annual ColorMetrix user’s group conference in Las Vegas August 21-23 at the Mirage resort and casino. More information is available at (http://www.colormetrix.com/cmug05). We also have a session planned in which we will discuss the difference between the many light sources (illuminants) available in the graphic arts industry.\

Well, that’s it for week 4. Please feel free to e-mail back (raffelj@colormetrix.com ) and let me know what you think. If you have ideas for golden nuggets, that would be great too.