I LUV UV
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This reserved article originally appeared in CHROMiX ColorNews Issue 47 on February 28th, 2012.
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an article by Pat Herold, CHROMiX Technical Support
As Tom Lianza of X-Rite says, "the whole UV issue is like a wound that won't stop itching." A couple of new standards have come on the scene which can change our viewing environment and give us more options when saving measurements. We wrote an article on optical brighteners in issue 36 of the CHROMiX ColorNews. We hope that this new article will provide a kind of Calomine lotion as we forage through these new UV developments.
If you recall, when we last looked at Optical Brightening Agents (OBA's), we saw that they can be present in many of the papers (and some of the inks) we use for printing. These OBA's are also known as Fluorescent Whitening Agents (FWA's). I don't know which term I like better. I might decide to use them interchangeably in this article just to confuse you, so you'd better read carefully.
FWA's are great in that they make our paper "whiter" - but they do cause problems since that brightening will change depending on our viewing environment and our eyes see this white differently than do the measuring instruments we use to measure color.
If you are printing on paper that has a lot of OBA's in it, the profiles you build will likely make your prints a bit warmer in the brighter parts of the picture - unless you employ some means of correction. This can be a big issue for those who require great accuracy in printed color. The other half of the issue is that lighting conditions affect how much OBA's are detected. In other words, different amounts of UV in the light source will determine how much the OBA's in the paper are excited in the visible spectrum.
How to get it (or not)
In order for fluorescing to happen, you need to have a light source that contains UltraViolet light shining onto a material that has FWA's in it - to make the material "fluoresce". There are several different situations you could find yourself in:
- There may or may not be FWA's in the paper you print on or in the inks you use.
- In addition, there may or may not be UV light in the actual light you are using to view your prints.
- Your measurement instrument might be filtering out the UV light before it measures the color, (eg: a UV-cut i1Pro, a DTP70 with UV filter on, etc)
- or your instrument might be using an illumination lamp in its measurement process that has no UV light in it - and is effectively doing the same thing as "filtering out" the UV light. (iSis)
Your measuring instrument might be doing absolutely nothing about filtering out any UV light. This can be perfectly fine if:
- Your paper / ink does not have any OBA's
- Your software is making a correction for OBA's (i1Profiler, i1Match)
- Your prints will be viewed in such a way (under non-UV light for example) that it will not affect the viewing experience, or
- You just don't care.
Back before we started using more paper with FWA's, we could get away with not caring most of the time. But a new viewing standard was recently implemented that affects how you'll be viewing prints in a viewing booth.
Paper and Proofing
In the world of large volume printing, you have your printing press which is a big beast of a machine that is rather costly to run, considering the paper, ink and other consumables. So when someone wants to know what an image will look like when it's printed on a press, they use a proofing printer - a printer capable of producing single prints at a fraction of the cost of firing up the whole press. This proofer is specially tweaked to look just like the press, so you can print your image on this "proofer" and get a "hard proof" that is supposed to match the press reasonably well. These proofers, whether they be a Kodak Approval or a high quality inkjet printer, make use of "proofing paper" to accomplish this feat.
Due to the fact that a printing press is a much different machine than a proofing printer - different inks, different printing technology - you usually can't print on the proofer with the same paper you'll use on the press. So you use proofing paper that is specialized to work on that printer and closely simulates the color and texture of the paper that will be run on the press. These high quality proofing papers are traditionally made specifically without optical brighteners. This is to increase the permanence of the image as well as taking the erratic UV issue out of the picture. (Regardless of whether the light in which you're viewing this proof has UV in it or not, the print will look the same. ) Okay, here comes the funny part: Proofing papers typically do not have OBA's in them but press stock frequently does. Hah!
Not to worry, say the pre-press guys. Our viewing booths have lamps that are specially made to not emit light from the ultraviolet spectrum. So the press paper (with FWA's) will look the same as the proofing paper in our light booths. Hah! Right back at you!
(This reminds me of the old joke about the guy selling an African elephant charm. He said it was guaranteed to repel elephants in case of a stampede. When his customer protested, "there aren't any elephants within 30 miles of here," he replied, "See how well it works!" It is rather hard to fault his logic, but it somehow did not seem to be a fair test.)
Add ISO 3664 excitement
While this worked out well for the press side of things, someone realized that these viewing booths did not match normal, in-the-world, daylight viewing conditions. Once the image got out "into the sun" the optical brighteners would be excited and you'd have a brighter, bluer image than was expected.
ISO 3664 is the international color viewing standard for the graphic technology and photography industry. It was updated in 2009 to have more stringent requirements, so the light source would more accurately simulate the CIE D50 (daylight) illuminant in the UV range. The old standard was loose enough to allow for little or no UV light. Basically, because sunlight has UV light in it, this new standard requires a certain amount of UV to be included in these new lamps. This new standard does a better job of giving you viewing light that is more realistic.
Since the new update, lamp manufacturers have been busy reformulating lamps in order to match this standard which was implemented on January 1, 2012. As of now, all viewing booths professing to be compatible with the ISO 3664 standard will have these new UV-using lamps included, including these from GTI and Just Normlicht.
In other words...
The situation as it was:
Proofers would use proofing paper with no OBA's in it. They would print onto press paper that oftentimes had OBA's in it. Viewing these two in a press-side viewing booth would allow these two images to appear the same. This also made it easier to have proof-to-proof matching.
The situation now (as of January 1, 2012):
Proofers are still using proofing paper with no OBA's in it. The press is still printing onto paper with OBA's in it. The viewing booths have more realistic UV-including lamps. These prints are no longer matching in viewing booths. Customers are getting more realistic views of what their prints look like under normal daylight. Proofers are having a harder time getting their proofs to match the press. They are getting frustrated when their clients perceive their proofs as being "less accurate."
If you happen to be in the client role in this scenario, you might cut your printer some slack. There are some changes in the industry and it will take a while to find the best path forward. The easy solution for proofers is to use the same stock that is used on the press. But that can be harder than it sounds since there are different inks and different printing processes involved. A second option is to find proofing paper with a similar level of OBA's in it. Finally, some profiling software allows one to dial in a profile so that it visually matches what you see on the press. (See our article on X-Rite's OBC module.)
ISO measurement modes
Part of the reason why the industry has taken this step toward more requiring more realistic UV in our light sources, is because we now have more instruments that can measure UV and more ways to deal with it in creating profiles.
2009 also saw the revision of the standard which deals with how to take measurements of color in the graphic arts industry (must have been a good year for standards). ISO 13655-2009 introduces four measurement conditions which you might start seeing cropping up in your newer measuring software.
M0 delineates that the measurement was made using "illuminant A" which is the traditional tungsten lamp. Most of your older instruments would have this kind of lamp (ie: i1Pro, DTP41, DTP70, Spectrolino). M0 does not define UV content. As a result, M0 can be thought of as the fall-back condition for instruments not conforming to M1 through M3 - including older UV-cut instruments that don't conform to the specific UV filtering of M2.
M1 specifies the measurement light as being D50, that is - normal daylight. This would include a specific amount of UV light, and not be polarized. As of now, there are very few instruments that conform to this measurement condition (the D50 spectral curve is difficult to produce). Two that do are the BARBIERI Spectropad and the Konica Minolta FD-7.
M2 describes any non-polarized light that has UV filtered out. This includes measurements made by XRGA-compatible instruments in UV-cut mode but NOT older instruments. The UV filter is carefully defined and most older UV-cut instruments are not compliant.
M3 is for measurements that are polarized (and are assumed to have the same UV filtering as M2). Polarizing the light as it is measured can be used to reduce the way the surface of the media bounces light back up to the sensor, and can draw more shadow detail from some difficult media substrates like canvas and matte papers. It also almost eliminates the difference between wet and dry measurements and is useful for those who need consistency between on-press and older work.
The new i1Profiler software has the ability to save its measurement files in these four different "measurement modes." You will most likely see M0 and M2 used, depending on what instrument you are measuring with of course.
These new modes show up when you save a measurement. The label for each mode is included in the name of the measurement as well as in the header information in the measurement file itself. While it's still too early to tell what impact these modes will have on the industry, the intention here is that they will do a better job of communicating the purpose for which the measurement was taken.
It's tempting to see change as a threat, and it's certainly possible that devious minds will mask subversive plots by appealing to change. But I don't think anything so sinister is happening in the color world. Ideally change happens because of a sincere desire to improve things or react better to changes that have already taken place. At CHROMiX, we are devoted to bringing you information on the noteworthy changes that are happening in the industry in a truthful and easy-to-digest manner.
Thanks for reading,