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w∆Ch fail with Curve4

  • 1.  w∆Ch fail with Curve4

    Posted 23 days ago

    Reading a TC1617 chart on a Mark Andy HD digital press for G7

    Within Curve4 everything else (Targeted and Colorspace) is passing - just a w∆Ch fail.

    Tried re-profiling from scratch (GMG), tried re-calibrating profile, various substrates - and pretty much a consistent w∆Ch fail each time.

    What do I need to think about adjusting or changing to get a pass?

    Thanks,



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    Randy McDonnell - G7 Expert
    Prepress
    Kwality Labels Inc
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  • 2.  RE: w∆Ch fail with Curve4

    Posted 23 days ago

    Yes, it is possible to pass on overall dE to the color space target yet fail on the rather stringent gray standard--and obviously vice versa. Prioritize gray balance in building your curves. The guidance is in your data.

    Mike



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    Mike Strickler
    MSP Graphic Services
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  • 3.  RE: w∆Ch fail with Curve4

    Posted 23 days ago

    I should have mentioned that if your target color space is not normed to G7 gray balance and tonality (as are the GRACoL profiles) the divergence between color space and G7 dCH and NPDC compliance could be considerable. I don't know what you mean by "calibrating" a profile in GMG, but be sure that the target color space is G7-aligned.



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    Mike Strickler
    MSP Graphic Services
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  • 4.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Your w∆Ch average and max failure is peaking between 20–50% tonality. In my experience, this could be ink trapping issues. I'd recommend using a loupe to look at the overprinting dots in this range. Look for skipping or irregular dot patterns, as shown in the example images.

    Additionally, I'm noticing dot loss in the highlights, which is also a sign of mechanical ink laydown issues.

    One last tip is to scan and verify both the P2P and IT8.7/5 data to make sure the chart you are relying on has no issues and that both exhibit the same failure. Also, check if the press can pass G7 gray balance without color management or G7 curves alone to determine if the color transform is causing the issue.


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    Tim Quinn
    Nazdar Consulting
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    ------------------------------
    Timothy Quinn
    Consultant
    Nazdar Consulting Services
    Shawnee KS
    816-582-6748
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  • 5.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Great analysis, Tim. 

    Question: would his press even be capable of skipping or irregular dots? I thought that type of press did a good job at eliminating such factors. 



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    Brian Tickenoff
    PrePress Manager
    Coyle Reproductions Inc.
    Brea CA
    (866) 269-5373
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  • 6.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    I'm assuming this is printed on pressure-sensitive paper and film, which could have ink or substrate anomalies where tones start to stack. There's excessive highlight loss, but the peak delta starts at 20% and recovers at 50%. You should also review the color management polices and GCR settings, 20% is typically where K starts. You won't know for sure until you verify G7 capability without color management. Keep us updated on your findings!



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    Timothy Quinn
    Consultant
    Nazdar Consulting Services
    Shawnee KS
    816-582-6748
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  • 7.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    I would review not just CM settings but driver settings as well, particularly ink limits. 



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    Mike Strickler
    MSP Graphic Services
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  • 8.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Try turning on Native CMYK. Sometimes the 3 color gray don't blend well. See if that works.



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    Donald Barr G7 Expert
    Color Management Consultant
    SK Digital Services LLC
    Lusby MD
    (443) 624-4578
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  • 9.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Native wouldn't help because his 100x3 ink is nearly 0,0.



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    Timothy Quinn
    Consultant
    Nazdar Consulting Services
    Shawnee KS
    816-582-6748
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  • 10.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    IIRC, the digital press colorspace qualification is the same as for a conventional press, which does also require a grayscale pass. I have sometimes seen this issue when working with inkjet proofers, in which the normal profiling and iterative optimizing fail to dial in the gray balance as much as expected. Usually there was an issue outside color management that was at fault, e.g., with the driver. I like Tim's suggestion to disable color management, and  in this condition I would apply the curves suggested by Curve and check the result. Then I would profile on top of this. This is the recognized best practice for conventional presses and may help in this case. Then of course you can iterate as before if this further improves the result. I should add that you shouldn't reverse this order and apply G7 curves on color-managed output. It doesn't work!



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    Mike Strickler
    MSP Graphic Services
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  • 11.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Thanks to all for your comments and suggestions.

    Native CMYK on/off didn't change anything.

    The substrate is white BOPP.

    Both P2P51 and TC1617 show similar results (fail).

    Not seeing ink trapping or skipping issues.

    This is Mark Andy HD digital press that is being color managed via GMG ColorServer Smart Profiler.  Creating a new profile from scratch does not change the result.  GMG also has a recalibrate function that 'fixes' existing profiles back to their original - which helps when initially passing G7 and now the profile has drifted.  This recalibrate did not change anything.

    We run this TC1617 chart every 4-6 months to confirm our profiles are still within g7 specification.  Run it for all the various substrates and profiles we have.  If is fails, we first try to fix with a recalibrate and if this doesn't solve the issue (as is the case here) we build a new profile from scratch.  

    This is the first time ever over a few years now that a failed G7 reading was not fixable by rebuilding a new profile from scratch or a recalibrate.  Other profiles are passing G7 currently.  We follow a strict procedure so that any new profiles have the exact same settings each time around - nothing has changed in our color management.  

    This particular iteration is V8 meaning the 8th new version of the same profile for this substrate over time.  7 previous times, no issues, hit G7 right away.  This 8th time, no such luck.



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    Randy McDonnell - G7 Expert
    Prepress
    Kwality Labels Inc
    Richmond Hill ON
    (905) 780-9496
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  • 12.  RE: w∆Ch fail with Curve4

    Posted 22 days ago

    Interesting. So how do results look before the iteration in GMG? Is it already looking problematic, with higher-than-expected dEs for that stage? Is so, something else is going on in your print process that is making it hard to make a good output profile, and this will limit the improvement possible with further profile tuning. Can you share the results from a fresh, non-iterated profile?



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    Mike Strickler
    MSP Graphic Services
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