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Press Gain Compensation Curves - how many should we have?

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  • Press Gain Compensation Curves - how many should we have?

    I'm been running Rampage (v10.4) for about a year now, on s system that was installed in 2007. We're experiencing some odd issues, with highlight dots (below 5%) disappearing when we output plates (CTP). Native files shows that the data is there, so does the printed proof and the on screen preview/proof. We re-linearized the plates but still have the problem. We ended up just editing the Photoshop files to compensate for the loss just to get the job on press. Since then we did some digging, and there appear to be significantly different Press Gain Compensation Curves for each of the process colors. Is this correct? Does it stand to reason that since the system is processing a 1-bit image, regardless of separation color, that the curve should be the same for each separation running on the same press. We have three presses, so I see that there should be a different curve for each press, but not for each process color on the same press...

  • #2
    Re: Press Gain Compensation Curves - how many should we have?

    My RAMpage is also set up that way. If your losing highlight dots, I'd check the chemistry first. What plates are you running?
    Do the linearized plates read from 1% to 99%?

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    • #3
      Re: Press Gain Compensation Curves - how many should we have?

      Plates are Fuji LP-NV2. Yes, they are linearized from 1% to 99%. Chemistry is fresh. The dots are "disappearing" because of the compensation curve, not through any problem with the plate or processor. 1% dot is set for 1.6 (cyan), 2.2 (magenta), 1.4 (yellow), 2.1 (black) . 3% dot is 5.9 (C), 6.3 (M), 5.2 (Y), 7.1 (K), 5% is 9.6 (C), 9.7 (M), 8.8 (Y), 12.3 (K). It was the 1-3% area that was the problem with our job. I had to tweak the images in Photoshop to get a minimum of a 3% screen in the highlights to get anything to show up on the plate.

      Does anyone have any idea why there are different Press Gain Compensation Curves for each separation color?

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      • #4
        Re: Press Gain Compensation Curves - how many should we have?

        Ok what part of the curve? Both the Actual and Desired need to be seen.
        Mine are
        Desired
        Des C 1.0 5.0
        Des K 1.0 4.0
        Des M 1.0 5.0
        Des Y 1.0 4.0

        Then the Actual

        Act C 1.0 6.5
        Act K 1.0 5.0
        Act M 1.0 4.5
        Act Y 1.0 5.0

        I had issues as well with these new plates but mine was with the RAW numbers. For some reason I'm getting 64% @50% on the RAW test. Fuji says it's supposed to be like 52%. They spent about a month trying to figure it out and never found an answer. I can linearize, but have to really watch my chemistry or my numbers go off.

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        • #5
          Re: Press Gain Compensation Curves - how many should we have?

          The different curves for each separation on your plates is exactly as it should be. Whether they are accurate values, or not, is another matter. The point of the compensation curve is to improve deficiencies on a specific press. This fingerprinting process involves running a target image to standard press densities, then scanning the press sheets and reading the dot gains. If the readings indicate that a specific color (cylinder) is running above or below a certain standard (Gracol, Swop, etc.) then a unique curve is built to compensate for this press problem. Usually, maintenance and wear issues on press require that a new curve be created at least once a year... sometimes more if no strict preventative maintenance procedures exist in a press room.

          Of course, I'm assuming that this fingerprinting procedure was done in your shop years ago. You probably just need a new curve that reflects the current condition of your presses.

          We've been creating custom compensation curves for years. It's a pain in the butt because you can end up constantly chasing a moving target, but when prepress and pressroom agree to maintain some standards, it works really well.

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          • #6
            Re: Press Gain Compensation Curves - how many should we have?

            >Does anyone have any idea why there are different Press Gain Compensation Curves for each separation color?

            Not unsual really. Might need or want individual separation curves to hit target gains for those seps, to acheive gray balance, or perhaps as a result of an intended versus actual press calculation. Shouldn't be losing dots though, Did this come on suddenly, or has it always been the case?

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            • #7
              Re: Press Gain Compensation Curves - how many should we have?

              We don't even have desired curves set up, except for our proofers. We had serious problems with the new Fuji plates as well. They never said anything about the plates changing and one day we everything went haywire. We wasted two boxes of plates and two days of press time trying to figure it out. They had to send up a tech for two days to fix the problem. He had to reset the processor, changed the timing and temperature.

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              • #8
                Re: Press Gain Compensation Curves - how many should we have?

                This is the first time we've run across it, but the curves have been in place since everything was calibrated, early in 07.

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                • #9
                  Re: Press Gain Compensation Curves - how many should we have?

                  I wonder if someone deleted your desired curves? They are part of the equation and I don't think you can make proper plates without them. You may as well just run linear if you don't have the whole thing set up.

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                  • #10
                    Re: Press Gain Compensation Curves - how many should we have?

                    Jud,

                    I think almaink is right on the money. I see that you said you don't use Desired curves, but are you using Actual curves along with your linearization curve? If you use Actual without Desired it WOULD blow out your highlight dots.

                    Erik

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                    • #11
                      Re: Press Gain Compensation Curves - how many should we have?

                      At one point there was an environment variable that you can set in the shooter app. I've seen extreme highlight dot disappear, usually due to the curve being applied, bad processor scrubber roller pressure (too much can remove a lot of those very light dots), or bad chem (which you said was not the case). Did this show up suddenly, been this way all along, or just get noticed recently?!

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                      • #12
                        Re: Press Gain Compensation Curves - how many should we have?

                        We went from LP-NV to LP-NV2 plates with just a new linearization curve, and they have been running great ever since (4 mos.).
                        It seems odd that your Fuji rep never said anything about the new plates, but maybe the info never made it to the right people. We are also running Rampage (V10.5) and use a linearization curve, and seperate CMYK actual and desired curves, and the pressroom also reports that the LP-NV2s are running really well. We had highlight stability issues with the LP-NVs, but not these new plates. The curves need to be different for each color because the press will gain differently in each color, and each unit for that matter. Our presses are set up to print really close to each other, so we are able to get away with just one set of curves.

                        How are you checking the plates? I use the Rampage scale imposed 6 or 8 out, run a linear plate to verify, then turn on the actual and desired curves and run another plate. I use a chart that I made up after we ran the press characterization, so I know what my end goal is. If my plates are within tolerance, I know it's a press problem.



                        David Watson
                        Edwards Printing Co.
                        610-539-1991

                        www.edwardsprinting.com

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