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To curve color bar or not

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  • To curve color bar or not

    what do people say. To put the curve (target profile) on the color bar or to leave it linear...Whacha think?

  • #2
    Curve.

    Since you are curving your plates to achieve a target press response then the color bar should be curved.

    (the issue about the value of what the color bar tells you is debatable)
    Last edited by gordo; 11-05-2018, 08:45 PM.

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    • #3
      Who needs the color bar more; pre-press, or the press operator?

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      • #4
        You would need to curve the bar. I do agree with Gordo on the true value of the color bars on press, but sometimes it's all you have.

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        • #5
          Originally posted by gordo View Post
          Curve.

          Since you are curving your plates to achieve a target press response then the color bar should be curved.

          (the issue about the value of what the color bar tells you is debatable)
          I have always tended to think about colour bars as a process control issue of how the press is running and not specifically a colour target management issue, although I can see it does not matter as long as one knows what the final value should be.

          If one uses a colour management approach that did not use curves but one that got the desired screen values via a ICC profile or other LUT then a non curved colour bar would seem to be the proper approach.

          IMO, the real goal is to make the process so consistent and predictable, that no colour bars would be needed and therefore paper could be saved.

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          • #6
            Historically, the color bar was used as a process control device - file, file to film, film to plate, plate on press. You started with known tone values in the color bar and you had an expectation of how those values would be distorted as they went through the production process. If those values did not meet expectations then you knew there was a problem that needed fixing.

            From a press operator’s point of view the only color bar elements that they care about are the solid ink patches. That’s why many color bars just have solid patches. From a prepress point of view, the color bar is mostly used as a diagnostic tool if a job fails on press. Its various patches can give an insight into why.

            Sometimes there is no room on the job for a color bar, but the job is run anyway. This often happens in magazine work. Sometimes the color bars are hidden as graphical elements in the live image area. This often happens in newspaper work.

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            • #7
              Originally posted by gordo View Post
              From a press operator’s point of view the only color bar elements that they care about are the solid ink patches. That’s why many color bars just have solid patches.
              I know many press operators who would disagree with that statement.
              Screened patches of known values are nice to use when determining dot gain.

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              • #8
                Originally posted by MacTwidget View Post

                I know many press operators who would disagree with that statement.
                Screened patches of known values are nice to use when determining dot gain.
                Press operators aren't necessarily truthful or forthcoming to "outsiders" in describing what they actually do.

                From a press operator's point of view, their job is to align the live image area of the presswork to the proof. The color bar is cut off and goes into the recycling bin.
                Their main controls are solid ink film thickness, water, and ink transfer integrity. So those are the things they focus on.
                They'll measure SIDs in the color bar. For everything else they do a visual inspection of the live image area under a loupe.

                Inspection.jpg

                Every graphic element in the live image area tells the press operator what they need to know about water and ink transfer integrity and has much more actionable information that any single color bar. That's why you see them constantly doing what is pictured above.

                Dot gain, as measured from a color bar, is not very useful a metric for the press operator, which is why they typically don't measure it. Dot gain, after all, is not a press operator's target. Aligning to the proof is.
                Dot gain, , as measured from a color bar, may have some value for prepress - or a QC specialist - to help diagnose a job that has failed on press. But for the pressroom, it's usually a waste of time.

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                • #9
                  Here's an example of what I mean by the color bar and dot gain and why the press operator concentrates on SIDs (and not dot gain) in the color bar and water and ink transfer integrity in the live image area.

                  Dots.jpg

                  The left and right images show the cyan printer on a single press sheet.
                  According to the color bar the dot gain is spot on.
                  And the color in the live image area aligns with the proof.
                  But there's an obvious ink transfer problem on the right side of the press that needs to be fixed.

                  That's the sort of thing that concerns the press operator. That's the sort of thing that the loupe is used for.

                  Last edited by gordo; 11-06-2018, 01:02 PM.

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                  • #10
                    Originally posted by MacTwidget View Post

                    I know many press operators who would disagree with that statement.
                    Screened patches of known values are nice to use when determining dot gain.
                    From an operator’s perspective, absolutely. Trapping, doubling, and slur targets are just a few of the patches that are convenient to have. One of those being extremely useful over any of the others. It’s all just personal preference, of course, and isn’t completely necessary. But then again, neither is a curved color bar.

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                    • #11
                      Originally posted by alibryan View Post

                      From an operator’s perspective, absolutely. Trapping, doubling, and slur targets are just a few of the patches that are convenient to have. One of those being extremely useful over any of the others. It’s all just personal preference, of course, and isn’t completely necessary. But then again, neither is a curved color bar.
                      I hope that the folks who built the planes I fly on didn't choose their manufacturing process controls based on their own personal preferences.

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                      • #12
                        Originally posted by gordo View Post

                        I hope that the folks who built the planes I fly on didn't choose their manufacturing process controls based on their own personal preferences.
                        To some degree, they probably did. Whenever there's more than one way to do something correctly, wouldn't preference then become a factor? That doesn't mean that consistent quality is achieved by chance, though.

                        I think that certain patches in a color bar are absolutely necessary, and others are a matter of preference...

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                        • #13
                          Hello fellow Lithographers and the Pre-press Brigade (Curves and yet more curves)


                          PRINT CONTROL STRIPS (COLOUR BARS) and PLATE CONTROL EXPOSURE TARGET (PCT)


                          Salient Points: Be they FOGRA, Ugra or GATF, Print control strips (Colour Bars) all include elements within that

                          highlight press problems.


                          Fundamental that the - FIDELITY of the STAR/SLUR Target remain true.


                          Plate Control Target (PCT) - is a very precise test image used to diagnose, calibrate and monitor plate Imaging steps.


                          Footnote: most of these helpful targets have their origins from the Geman Optical Industry.


                          Do not use Halftone Reproduction Curves.



                          Regards, Alois


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