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What about UV?

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  • What about UV?

    Larry Warter of Fuji has said:
    "Highly brightened Grade 1 papers make color management virtually impossible unless you proof on the production stock"

    What is the effect of UV on spectro measurements? Do you use a UV cut filter when making profiles? Do you consider/compensate for the difference between UV content in proofing papers vs press papers? What is the impact of UV/optical brightners on the proofing/color management process?

    thx, gordo

  • #2
    Re: What about UV?

    Wow Gordon, you certainly have opened yourself a can of worms! I certainly don't know the answers, but I do have a few comments on this messy, messy subject.

    The main reason I think this subject is so messy is that optical brighteners, UV content of light, and how different measuring devices respond to both is currently not quantified or standardized in any meaningful way. There is no standard terminology or grading system for paper that describes its response to UV, and there is also no standard for how much UV should be in say a D50 illuminant, or the illuminant that is inside a spectrophotometer. Then to complicate things further, different spectro's react differently to the brightening effect.

    I have personal experience with the last statement, as we have both an i1Isis chart reader (which can provide both UV-cut and UV-in measurements) and and a UV-cut i1pro handheld, and I have occasional access to an i1pro that does NOT filter UV. When reading the LAB value of white of dozens of stocks that we have in house, I find that the UV-cut numbers between an Isis and I1pro match fairly well. But when UV is INCLUDED the Isis sees the paper with brighteners as bluer (lower b value) but no change in brightness (same L value) when compared to the UV-cut numbers. The I1 handhelds, on the other hand, see papers with brighteners as both bluer and brighter, and the b value tends to be roughly 2 points lower than the same paper on the Isis.

    You asked: +Do you consider/compensate for the difference between UV content in proofing papers vs press papers?+
    Because of all of the above, I find it is very difficult to do this in a meaningful way.

    +Do you use a UV cut filter when making profiles?+
    Many people will maintain that UV should NOT be filtered out, because it is a real effect and there is UV content in virtually all light, so removing UV will make your profile less accurate. However, such a profile will be based upon the amount of UV in your spectro's illuminant AND how your spectro reacts to the brighteners, so it is limited in that it doesn't necessarily characterize actual viewing conditions. A good retort to this is that however UV may be incorporated into the process, it will STILL be more like real-world conditions than cutting UV entirely. I tend to agree.

    +What is the impact of UV/optical brightners on the proofing/color management process?+
    I think the quote from Larry exaggerates the situation somewhat, but he is basically correct in that the unquantifiable nature of optical brighteners throw a monkey wrench into color management. The unbelievable truth is that you have to do WHAT WORKS BEST FOR YOU. Larry's suggestion of proofing on the production stock is the only way of removing the biggest variable in the equation: the amount and "kind" of optical brighteners used. If you can use the same stock for both, I would definitely Include UV when profiling. If you can't proof on the production stock, the sad truth is that you you should make UVin and UVcut profiles and see which one matches better in your viewing conditions.

    I've heard several color management experts say that when it comes to including UV or cutting UV, it really comes down to personal choice. Whatever produces better results for you in your particular circumstances is what you should do. One rule you can definitely follow is that you shouldn't mix the two kinds of measurements and profiles: pick a route and stick with it.

    -Todd Shirley


    • #3
      Re: What about UV?

      Hi Todd,

      Thank you for your considered response. Because this seems to be a significant variable in color management implementation it would seem to create an opportunity for confusion press side when color doesn't not align with the proof because of the difference in optical brightners between proof substrate and press substrate. Not just because of how the original profile was created but also from the fact that press inks act as UV cut filters. I.e. As you go through the tone scale from 100% ink to 0% ink - the greater the UV component forms the color you see.
      Here's a photo of a proofing vendor's swatchbook under 5000K (left) and Black light (right)


      I've gotten rid of the vendor's name because it's not important.
      If you cannot proof on the actual printing substrate, would it be a good idea to check the proofing media optical brightner content with something as simple as a blacklight to see if it is at least similar to the brightner content of the actual final substrate?

      thx, gordo


      • #4
        Re: What about UV?


        Just some comments.

        One can not see UV light. As I understand the problem, the UV light results in fluorescence in the brighteners. This then is basically not reflection but light being emitted at a different wave length from UV. It is as if there are light sources in the paper. This then causes all those kinds of colour matching problems stated before because there is probably no standard UV component in the standard viewing illuminant. Maybe it could be standardized and dealt with in some consistent way.

        My point is that you are not seeing UV light but light in other wave lengths due to fluorescence.

        But now you also introduce another interesting issue. You have taken photos of a target with 5000K illumination and with black light (UV). The camera has captured the images.

        Is it also possible that the camera rgb receptors are not only picking up the reflected light, the light from fluorescence but also reflected UV, which we would not normally see. Taking a photo might complicate the problem even more.

        I am not sure how much the printed inks would filter out UV light. Normally the maximum reflection would be equal to 1 by definition. This means that all the illumination was reflected back. It is logical to think that due to fluorescence, more light will come back to the densitometer or spectrophotometer than was projected on the target in that wave length by the instrument's illuminant.

        I have seen where printed ink jet yellow seemed to measure at a higher value of red region than the paper itself. In this case I suspect that the yellow ink itself had fluorescent materials in it. The problem with fluorescence may not only be with the brighteners in the paper.


        • #5
          Re: What about UV?

          Hi Eric,

          Yes, sometimes it's not just the substrate but the press ink. Here is a VanSon ink swatch in normal light and in UV:


          The photo correlates with what one see under the UV illumination. Note the glow of the yellow ink compared to the other process colors. This fact is not explained in the data sheets for the ink. Until you see the ink under UV light you wouldn't know that the yellow is different, from a fluorescence point of view, to the other process colors in the series. BTW, I've seen the use of a fluorescent yellow ink in newspaper printing. I assume to add vibrancy to the the 4/C printing.
          It's an interesting topic that, like many issues in printing, I don't think has seen much research.
          It means something. But I'm not sure what.



          • #6
            Re: What about UV?


            I am glad to hear that the photos correlates with what you see. It was a possibility but fortunately not a problem.

            This issue of UV is very important. I am quite sure that without fluorescence in the inks and paper, managing colour can be quite predictable and straight forward. It would basically be reflectance.

            But having fluorescence as a factor is a real problem. For one thing, as far as I know, there is no standard viewing illumination that has UV included as a rated value.

            Also, the measuring instruments are not designed to deal with UV in such a standard way. If one can not suitably standardize the measurements, one can not provide a characteristic set of data to describe how the press prints or if one target matches the other. Therefore there is a lack of predictability.

            This does need research but I have little confidence in the technical community analyzing and then innovating a solution. Too many technicians but very few really good and imaginative scientists. History will show, whether people believe it or not, that the scientific and technical community in printing can not understand and solve problems. Lots of technical talk but little fundamental understanding.

            It was interesting to see in your photo how much fluorescence was in the yellow ink. I can imagine it being in other inks without people knowing. It is going to make things tougher.


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