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)
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.
In #53 I listed a bunch of color resources I had found on the web. I was looking because we are putting the finishing touches on the first beta release of our ProofPass.com soft proofing verification module. For me this project has turned out to be about the journey not the destination. Of course the destination which is a viable commercial release of the aforementioned product that we hope to make lots of money on is not a bad place to end up.
The Journey, however, has been like going back to school for a guy so grounded in the color science of the physical ink on paper side of our industry. I have come to the conclusion that a monitor is just another “black box†that creates color from my perspective. Just like a hard copy proofing system, a conventional printing press, or even a digital printing press is. So, that means if it can be measured it can be controlled.
The key to successful soft proofing appears to lie in the color management behind the system(s). I recently had the opportunity to view and measure eight displays powered by the soft proofing technology of three vendors all in one place. All were powered by Macs, but the displays came from two manufacturers. In our quick and dirty technology demo three of these systems (all under the control of one organization) came in with a very tight peak Delta E of only about 3 between the systems.
Monitors using the other vendors soft proofing technologies fell further out (as the software was pre-beta at that time I am going to omit any further numbers). The verification module did, however, catch that one of the monitors had been profiled to the wrong white point (let’s just say I was pretty pleased with the new toy we built!).
Surround lighting and viewing conditions will make any quality soft proofing system work or not work. I have read papers on subject, I have tested it myself, and I have spoken to people who have done extensive testing of the systems. The less surround lighting (other than your 5000K light booth) the better. The surround and viewing conditions should be identical to the ultimate conditions when you make your monitor profile. One of the biggest factors I have seen to making a good or bad monitor profile is surround lighting.
It is clear to me that monitor proofing is here to stay in our industry, and is also highly viable when properly utilized. While I do not see monitor proofing replacing hard copy proofing altogether, I do see it replacing hard copy proofing in some applications very quickly. In other areas I see monitor proofing replacing many of the internal proofing iterations prior to the hard copy “contract proof†used press side. Much of this is going to depend upon how tight the deadlines are for being able to change copy, and the perceived quality level of the work being produced.