viewing conditions

#67 Metamerism: Hard copy vs Monitor

by JimRaffel on January 16, 2008

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.

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

by JimRaffel on September 22, 2005

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.

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Golden Nugget #4…Proper Color Viewing Conditions

July 9, 2005

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 [...]

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