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Spot Colors and Spectrophotometer

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  • Spot Colors and Spectrophotometer

    Hey, everyone. So it took a while to figure out why my spectrophotometer wasn't giving me accurate dot area readings for process colors. It resulted in having dot gain curves that were pulling the colors way too far back and causing light prints. But I got through that challenge and had it explained to me why a 50% dot patch will read back as 68% on the spectrophotometer and that's what I want.

    now I'm wondering how people go about checking their dot area coverage on spot colors? For example, if I am using 485 red at 50%. And that is gaining on press to be a 60% sized dot, the spectrophotometer will tell me that the dot area coverage is 75%. Far too much, so says the spectro. But I need to know for sure that the dots of this spot color are actually gaining to 65%. I need to know that when I make my dot gain curves that measuring a dot and getting a reading of 50% really means that it is indeed gaining and balancing out to 50% after my adjustment. But with the spectrophotometer giving me these heavier readings, I don't feel like I can ever know what I need to verify using this tool in this way.

    So what do you all do with spot color screens?

  • #2
    Techkon is cinducting a webinar soon on this very topic. Hope this link works:
    https://attendee.gotowebinar.com/reg...b&splash=false

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    • #3
      Originally posted by gordo View Post
      Techkon is cinducting a webinar soon on this very topic. Hope this link works:
      https://attendee.gotowebinar.com/reg...b&splash=false
      That is great. Hope they actually give up the info instead of just trying to sell a new spectrophotometer. Just signed up now. Thanks.

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      • #4
        I will be very interested in learning how one can reliably measure spot color tints. Color me SKEPTICAL as we all know draw downs / ink opacity and paper white will all F&%$ with any attempts to "share" what I get with you so you can do what i did. - When I worked at Pantone, we developed / manufactured a Pantone Duotone Swatch book - we even included a cute CD that had loadable Duotone presets that would *ahem* allow you to apply them to your images in Photoshop - yeah.


        Right. Like paying darts in a tornado.
        Michael Jahn - Slightly used PDF Evangelist
        Simi Valley California

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        • #5
          Originally posted by michaelejahn View Post
          I will be very interested in learning how one can reliably measure spot color tints. Color me SKEPTICAL as we all know draw downs / ink opacity and paper white will all F&%$ with any attempts to "share" what I get with you so you can do what i did. - When I worked at Pantone, we developed / manufactured a Pantone Duotone Swatch book - we even included a cute CD that had loadable Duotone presets that would *ahem* allow you to apply them to your images in Photoshop - yeah.


          Right. Like paying darts in a tornado.
          You've now taken responsibility for all the evils wrought by Pantone. ;-)

          Many, if not most printshops just use the Black curve for spot colors, others the curve for the closest process color that has a similar L* to the spot color being used. Maybe a dumb densitometer is a better way to measure DG than a spectro for spot colors. I think Esko says to linearize the spot color inks in their extended fixed palette solution. As is the case with much in printing there are a number of ways of not solving the problem.

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          • #6
            The spot color measurement metric that Techkon has added to their spectro is one that has been officially defined in a brand new standard, ISO 20654. The standard is based on work done by the SCHMOO group. (I am proud to say that I gave the group its name: Spot Color Halftone Measurement Optimization Organization.)

            The approach is a different formula than the Murray-Davies formula that we all know and love. It has been found that for many spot colors (particularly those that are either very rich or are pastel) that the Murray-Davies formula does a lousy job at measuring anything useful. The committee compared about ten other possible formulas, and the SCTV (Spot Color Tone Value) formula won in the press tests. The new formula gives tone curves that look much more even, and which does not require extreme plate curves.

            I wrote this paper on the topic four years ago.
            http://johnthemathguy.com/files/pdf/...ASpotColor.pdf

            I have given several presentations on the topic, and will be presenting at the next FTA conference about it.

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            • #7
              Originally posted by JohnTheMathGuy View Post
              I have given several presentations on the topic, and will be presenting at the next FTA conference about it.
              The Fall conference in St. Louis, MO in October?

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              • #8
                As I mentioned previously;

                05-12-2017, 06:37 PM
                Do I dare mention that we now also offer a new denso-spectro-colorimeter that allows the user to choose between the bad old Murray - Davies Dot Gain formula or the shiny new SCTV ISO 20654 method? Or just wait until someone asks why a checkerboard measures 68% or why M_D dot gain measurements don't seem to work on reflex blue and many other spot colors?

                Just askin'...
                ===============
                And yet again;

                07-20-2017, 08:04 PM
                Well, since you asked, the Beta Presto Spectro offers traditional Murray-Davies Dot Area calculation, or TVI, or Dot Gain as well as the shiny new SCTV (ISO 20654) . Details on our website;
                https://betascreen.net/products/beta...presto-spectro

                ===============
                We'll be at PRINT 2017 in Chicago next week, stop by and see it in the flesh(tone) for yourself.
                Always available to members of this group on our Free Ten Day Trial.

                ​​​​​​​I'm just sayin'...

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                • #9
                  Here you could find more information about the ISO 20654:2017 related to SCTV

                  Regards
                  Attached Files
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