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G7 2007 RGB Lab Numbers

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  • G7 2007 RGB Lab Numbers

    Greetings,

    I have decided, since I am in the middle of running G7 targets, to adjust my Lab values to the ones listed in the 2007 spec. They are not that far off of the 2006 values but I figure I might as well be as up to date as possible. I see that the RGB Lab values are not listed in the 2007 spec as they were in the 2006 "How To...". Does anyone know if those numbers are available?

    I am the pesky flexo printer that has discovered that while I can meet the solid CMYK values under both the 2006 and 2007 guidelines, I could not get a close to the RGB values as I would have expected to considering my solid CMYK dE's are less than 2 to the CMYK values. I am sure the problem is ink trapping, but I would like to know the new numbers so I have something to compare to.

    Thanks to all that answer.

  • #2
    Re: G7 2007 RGB Lab Numbers

    Hi Bill,

    I'm looking now at the 2006 Gracol G7 "How To" Guide, the 2007Gracol Spec, and the 2007 Amendment to ISO 12647-2. and they are all referencing the same Lab values for CMY (white backing). K changed from 16 on the How to to 15 in the 2007 spec, not sure why, but really meaningles anyway.

    As you know, the RGB overprint Lab values are not listed in the Gracol 2007 spec, likely because they are subordinate to the CMY targets and not controllable.by the press operator. The 2006 "HowTo" does list ghem however, (in the form of proposed LAB values that were adoted in a ISO 12647-2 amendment this year) so basically you have the data you need in the Gracal "How To" guide.

    You had previously told me off line that you were given ISO 12647-2 Lab values that did not match the G7 "How To" or 2007 spec. Not sure how those were derived, but they don't match anything I've got. (including the 2004 version of ISO12647-2 , ISO12647-6 for flexo, First, ect).

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    • #3
      Re: G7 2007 RGB Lab Numbers

      i know this is a very old thread, but when i read this;

      "RGB overprint Lab values are not listed in the Gracol 2007 spec.."

      1. I was not aware that anyone could 'overprint' using light, or perhaps, I was not aware that RGB 'inks' were invented, so I am baffled as to how or why the words 'overprint' and 'RGB' would be used in a sentance anyway ...

      but then again, I never understood how colors did not always need some 'opacity' or 'netural density' value either ...

      Please enlighten me as to what is meant but an "RGB Overprint Lab value"

      When I read this set of posts, I realize that application developers seem to actually think thay can display such a thing (and I do not think this is logical or possible using LUTs myself

      http://www.adobeforums.com/webx/.3bc3dcef
      Michael Jahn - Slightly used PDF Evangelist
      Simi Valley California

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      • #4
        Re: G7 2007 RGB Lab Numbers

        Overprinting a solid 100% magenta and a solid 100% yellow creates red (R).
        Overprinting a solid 100% cyan and a solid 100% yellow creates green (G).
        Overprintinfg a solid 100% cyan and a solid 100% magenta creates blue (B).

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        • #5
          Re: G7 2007 RGB Lab Numbers

          Steve's correct. More info: The 7 in G7 refers to the 7 solids: C,M,Y,K,CM,MY,CY (the last three have been referred to as RGB overprints or Secondary overprints)

          Don

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          • #6
            Re: G7 2007 RGB Lab Numbers

            Bill

            The ISO overprints are acheivable when printing CMY do you print that sequence?

            Peter

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            • #7
              Re: G7 2007 RGB Lab Numbers

              >The ISO overprints are acheivable when printing CMY do you print that sequence?

              FYI, not mentioned in this thread is that Bill is using Flexo inks.

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              • #8
                Re: G7 2007 RGB Lab Numbers

                Greetings,

                Before I started using G7 methodology we used to print YMC. But now I am converting, one plant at a time, to CMY.

                We had already experimented some with CMY ink order in our Ca plant, rebels that we are, and felt there were positive results.

                -Bill-

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