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G7 calibration

  • 1.  G7 calibration

    Posted 12-04-2020 05:37 AM
    Hi to all
    I'm writing from Italy, and as you can image here the standard reference procedure is TVI calculation defined into the FOGRA PSO specification. I'm working with G7 spec, and calibration and sometimes the result it's look more interesting than what we can have with the TVI.
    But, as all of you know, and as you can see in the picture attached (light color is the Gracol, other is F39), the TVI value for Gracol 2006 and Fogra 39, that means during the calibration we found a really nice calibration for the gray and for but the image looks more darker in the light area in comparison with the digital printing proof.
    In this case we cannot play again with G7, because the result it' far away from the proofing.
    Anyone of you have tried or have an idea to generate a target of NPDC that can match better the TVI curve of F39


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    Luca Morandi
    Process Calibration & Brand Owner Mgr.
    ColorConsulting Srl
    Saronno
    +393497614700
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  • 2.  RE: G7 calibration

    Posted 12-07-2020 09:43 AM
    Good Morning Luca
    Is the white point of your proofing substrate the same as the white point of your printing substrate?

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    Michael McGinnis
    RR Donnelley
    Menasha WI
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  • 3.  RE: G7 calibration

    Posted 12-16-2020 06:59 AM
    Dear Michel
    thanks for you reply, no proof and print production have 2 different white point, proof have b* =-2 and production paper have it at -7

    ------------------------------
    Luca Morandi
    Process Calibration & Brand Owner Mgr.
    ColorConsulting Srl
    Saronno
    +393497614700
    ------------------------------



  • 4.  RE: G7 calibration

    Posted 12-07-2020 03:02 PM
    Edited by Wojciech Bialkowski 12-08-2020 04:21 AM
    Hi, Luca

    The curves included in Fogra39 come from the period of validity of ISO 12647-2 where curve A was determined for positive films. Typically in Europe a POSITIVE film was used - and this resulted in the copying process on an offset plate reducing the points in the lights. The effect of this was, therefore, a lower dot gain in the lightest tones on the print. NPDC was created from the very beginning on CTP systems. NPDC was determined from a "pseudo TVI" curve based on the CMY grayscale using a combination of the Sin and Cosine functions. It was called "SiCoTVI". So the SiCoTVI curve has a value / shape different from the FOGRA 39 curve. Therefore, the current A curve of the current ISO 12647-2 standard is different because it comes from CTP systems. Fogra created the reference characteristics of the Fogra 51. If you compare the TVI Fogra 51 with the CRPC6 - you will see that for CMY they are almost the same.

    Again, the "SiCoTVI" curve is constant and consequently you will not create another NPDC.

    Theoretically, you can create your own NPDC curve by changing the "SiCoTVI" curve but this will have nothing to do with the official G7 method.
    So I propose to create an EXCEL sheet by introducing all the math from CGATS TR015 and instead of "SiCoTVI" - experiment with your own curve by changing TVIcmy. In CGATS TR015, the document specifies this formula (10).

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    Wojciech Bialkowski
    Studio Omega
    Bydgoszcz
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  • 5.  RE: G7 calibration

    Posted 12-16-2020 08:14 AM
    Dear Wojciech
    thanks for your long explanation, really useful. I will try to generate a NPDC curve that can match better the F39 TVI, that make sense. I found the G7 method really useful as method for the calibration, but it's not flexible, as instrument when I need to match something that is not done in the same specification.

    ------------------------------
    Luca Morandi
    Process Calibration & Brand Owner Mgr.
    ColorConsulting Srl
    Saronno
    +393497614700
    ------------------------------