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TVI Shape When Printing Stochastic

  • 1.  TVI Shape When Printing Stochastic

    Posted 06-15-2018 02:23 PM
      |   view attached
    Hello,
    We have been experimenting with Kodak's Staccato dot and I have noticed a trend that seems to differ from when I fingerprint using an AM dot, the cyan gain seems to be much lower than the other colors.

    Is this common or do I have something else going on? I see the trend on multiple presses, stocks and inks.

    Thank you,

    John Stewart

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    John Stewart
    Freeport Press
    New Philadelphia OH
    (740) 658-4000
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    TVI Curves Stochastic.pdf   141K 1 version


  • 2.  RE: TVI Shape When Printing Stochastic

    Posted 06-16-2018 02:37 AM
    Hi John,

    I've not found this to be the general case with FM screens. In the examples you show, cyan TVI is greatly lower than magenta's only on some substrates; on others it's within 2% at 50%, which is insignificant. Bear in mind that TVI is affected by solid densities, so you always need to evaluate and correct those before even looking at TVI. If solid densities are weak you can have low TVI. You didn't say what sort of presses these were. On flexo solids may also be affected by impression strength and dilution of the ink, further exaggerating the effect. In short, yeah, I'd look elsewhere. TVI with linear plates is normally a good 15-20% higher than 150-175 AM, often even more. If you're down around 20% something else is going on, I'd say.

    Mike

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    Mike Strickler
    MSP Graphic Services
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  • 3.  RE: TVI Shape When Printing Stochastic

    Posted 06-16-2018 08:20 AM
    John

    I would suggest that you consider ink properties and chemistry. Cyan is typically better made than a blended magenta. TVI does not measure equally with Murray Davies on AnsiT on yellow or black. If you running densities above 1.5 or below 1.3 Murray Davies has errors.

    Also if you ink film is thicker or thinner this would show variation in TVI.

    Keeping substrate and tint the same measure several density solids. TVI being a ratio can change drastically.

    G7 is a much better method of control.

    See Iso 20654 SCTV. We have found with consistent ink film thickness and similar thicksotropic properties most inks respond the same!

    Steve

    Just a thought!

    Steve Smiley
    SmileyColor & Associates
    PO BOX 1015
    Bacliff TX, 77518 USA
    469-309-2025
    Steve@...




  • 4.  RE: TVI Shape When Printing Stochastic

    Posted 06-16-2018 01:40 PM

    John,

     

    Yes, stochastic/FM is quite different.  We HAD to use Curve 4 and a 25 point correction to get the gray balance correct.  Otherwise, the actual curves will depend greatly on your ink, the BATCH of that ink, the blankets, and chemistry.  ALL of that becomes more critical with getting stochastic corrected.  Once done, it is awesome!  You also need to test a range of dot sizes.  We tested Kodak, Fuji, Agfa, and Heidelberg plates, at 2 different dot sizes along with two chemistries and two different ink manufacturers to get down to what works best for us.  Because the dots are SO small it is very sensitive to getting it all right.  The results and stability on press once all that is established are really impressive.  Just brace yourself for some serious work, test/check frequently, and put controls in place for every step along the way to keep it dialed in once you get there.

     

    John Hearn
    Chief Officer of Possibilities
    Phillips Printing Company, Inc.
    949 Woodland Street
    Nashville, Tennessee 37206


    888 ask phil | philprint
    com

                  a d a p t a b l e

     






  • 5.  RE: TVI Shape When Printing Stochastic

    Posted 06-16-2018 03:55 PM
    I’m guessing that you meant to say “when Printing with FM dot....”

    Agreed, it has also been my experience that, when printing FM, the TVI values required to achieve proper Gray balance and NPDC are quite different from the TVI values required when Printing AM.

    Nominal/traditional AM TVI values will tend to produce low a* and b* values in the gray ramp when Printing FM.

    In general, Printing to G7 with FM screening will require lower-than-usual TVI in cyan and higher-than-usual TVI in magenta.

    Many will argue that TVI no longer has any place in the context of G7. This is true as far as it goes. In the world of lab Color, neither TVI nor density have any currency.

    However, until printing press manufacturers build a lab knob into their front panel, press operators with a job to do will continue to rely on density and TVI as real-world signposts and surrogates for the lab values that are the true targets.

    In this context, it is reasonable to provide the long-suffering press operators with traditional (density and TVI) targets derived from the more logical but also harder-to-grasp lab objectives.




  • 6.  RE: TVI Shape When Printing Stochastic

    Posted 06-17-2018 02:47 AM
    Yes, Glenn: With FM screens, TVI with linear plates is normally a good 15-20% higher than 150-175 AM, often even more-that was the intended meaning. I too see nothing wrong with with using TVI as the basis for the making the needed cutback curves, and most software gives no other option anyway.

    I think John's question was simply whether FM screening could account for radically different gain for cyan than MYK, and the answer is no. Whether gain is expressed as TVI or SCTV, it must be controlled.

    One small point regarding SCTV for norming process gain: The black curve will be too dark to pass G7 NPDC, so we should be careful about just tossing this out as a blanket recommendation to those who haven't been in on that particular discussion. An approximately 4-5% additional cutback on black will do the trick, however.

    More important point: One can generally pass G7 with "1D" curve corrections on FM plates, but this will not suffice to match GRACoL or other AM-screened output as the tints have not merely different gain but different hue as well, so as one moves farther from the neutrals the stranger the colors may look. This applies also two 2-color screened builds, especially greens, which will appear more saturated. The only proper way to control this is by profiling the press and inserting a device link in the workflow. So controlling the gain is actually John's first step, not the final one. Glenn wrote some excellent blogs on this point--check his website.

    Mike


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    Mike Strickler
    MSP Graphic Services
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  • 7.  RE: TVI Shape When Printing Stochastic

    Posted 06-18-2018 09:13 AM
    I'm sorry I wansn't 100% Clear All printing is offset 2400 dpi 20 Micron. The TVI shown was on my confirmation runs, I used the G7 method to create all curves and all were a pass for Targeted.

    The cover press is sheet fed with HUV inks.

    Thank you everyone for your input so far.

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    John Stewart
    Freeport Press
    New Philadelphia OH
    (740) 658-4000
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  • 8.  RE: TVI Shape When Printing Stochastic

    Posted 06-18-2018 04:12 PM
    When the TVI for one printing unit is out of line with the others, I recommend assessing the cylinder pressures. I have been helping companies implement a Nip Pressure indicator which assesses the pressure between the plate and blanket as part of their process control plan. It is done on a routine basis, and if dot gain on one unit changes, this is the first tool to reach for to ensure the "pressures" are where they should be; too much pressure (which is almost always the case) resulting in higher dot gain, as well as more friction, more electrical costs, more wear and tear, more heat and many other negative variables in the process. Company is Nip Control Systems out of Sweden, and they have a lot of good educational material on their site. Let me know if you want more information.

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    David Hunter
    Principal
    Pilot Marketing Group
    Forest Lake MN
    (651) 717-0590
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  • 9.  RE: TVI Shape When Printing Stochastic

    Posted 06-19-2018 02:29 AM
    Now this is even less clear. You wanted to know why your TVI was lower on cyan, which led one to think that you felt this was a problem. Now you are telling us, in effect, that the TVI is actually correct since the output is G7-compliant? All I can tell you is that you need to follow the correct order of operation and first optimize your solid Lab values and then go after halftone gain. If at the end of the process you pass G7, the curves were correct, regardless what the TVI is. Also keep in mind that the farther you venture from conventional AM screening (133-175 lpi) the looser the correspondence is between TVI recommendations and gray balance. The hue of halftones is affected by the screening along with sharpness of the dot and ink film thickness. Then there is the ink composition—large influence. Without looking at the actual data—and I mean spectral—it’s not possible to give a more thorough explanation of what you’re seeing.

    Mike




  • 10.  RE: TVI Shape When Printing Stochastic

    Posted 06-20-2018 09:10 AM
    Thank you everyone for your responses. I apologize that my initial questions was not as clear as it should have been.

    I was told that when we started experimenting with FM screening we would have some questions. Overall, we have been very pleased with the results, we are matching our proofs and customers are very happy.

    Thank you,

    John

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    John Stewart
    Freeport Press
    New Philadelphia OH
    (740) 658-4000
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  • 11.  RE: TVI Shape When Printing Stochastic

    Posted 06-28-2018 05:22 PM
    Your post reminded me of these graphs published in "Calibrating, Printing and Proofing by the G7™ Method Version 6 August 2006", in which case your TVI looks fairly normal!




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    Tim Quinn
    Nazdar Consulting
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  • 12.  RE: TVI Shape When Printing Stochastic

    Posted 06-29-2018 08:11 AM
    Thank you but the image is not showing.

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    John Stewart
    Freeport Press
    New Philadelphia OH
    (740) 658-4000
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