Tuesday, October 5, 2010

To linearize your CtP plates or not? Part four.

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  1. We have a two CTP, 1 plate and 2 presses situation. I use linearization to bring both devices to the same state since one is usually hot and the other is cool due to the age of the lasers. I use a second curve to average the presses to the same state. Since we use a tiff flow the adjustments needs to be made upstream of the CTP equipment. What would your experience tell you to do in this case?

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  2. @ destryer
    If I understand you correctly:
    Two different linearizing plate curves plus one common press curve (to target one averaged press condition). = Three curves total.

    You could go with:
    Two different plate press curves to target one averaged print condition. = Two curves total.

    Remember the film workflows that were the basis of the standards and specifications (SWOP, SNAP, GRACoL) that we are supposed to work towards. That was literally a one curve workflow - linear film - irrespective of the target press or condition of the vacuum frame. The established target for printing, even with CtP, is still a common, averaged target in terms of color and tone reproduction that any press in reasonable mechanical condition should be able to hit.

    So, in my experience most shops will have a common averaged print condition that their presses can all hit. They do not make different plates for different presses because doing that would be impossible as press time scheduling changes. Also, the more curves one has, the more complex curve management becomes and the greater likelihood of mistakes being made.

    In your case, if the press response is so different that you cannot hit a common target with one curve for both presses then you would have:

    Two different linearizing plate curves plus two different press curves (to enable the two presses to hit a common target e.g. SNAP). = Four curves total.

    or

    Two different different plate press curves for each CtP and each press to enable the two presses to hit a common target e.g. SNAP. = Four curves total.

    But if this was true then I would spend more effort in fixing the press issues that trying to overcome them with plate curves.

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  3. Hi Gordo. (related to my first post)

    I don't have preferences for Scenario 1 (1 plate curves) or Scenario2 (2 plate curves).
    In fact I well survived using Prinergy 2.x when there wasn't the possibility to have 2 separate curves.

    I understand and respect your point of view. But you know, including into Prinergy the possibility to handle 2 curves was a market request. And we did it.

    From my point of view is really important that Prinergy is able to handle both Scenarios (1 & 2), without any problem.

    Mathematically there is no difference using 1 or 2 curves. Sure, is a customer decision (related to his environment, number of plates, number of presses etc.) which method prefer.

    Cheers.

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  4. @ML,

    Yes, I know that having the possibility of using 2 separate curves was a market request. The important thing is that the decision as to whether to use a one or two curve workflow is not so much a technical decision as it is a business decision. So, it is important for the printer to think through the reasons and consequences in order to choose the method that is most appropriate for their needs. This thinking through process is often overlooked or ignored during workflow installation and implementation.

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  5. We use G7 calibrations on both of our presses, and initially did not use plate linerization as per their recommendation. Oddities with our equipment (eventually it turns out we had a laser issue) led us to start with linear plates for calibrations and we have been doing so for a few years now. We recently switched plates (and switched back for a few months while some issues were sorted) and were able to just linearize the new plates and proceed as usual with our individual press curves without any mucking about with a new calibration. Went pretty well and we were able to switch between plate types on a per-job basis with no real trouble, the RIP selecting the linearization for each plate type automatically.

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  6. Personally I do not see how what you did provided any better a result than you would have gotten by starting with uncalibrated plates. When you switched plates you would only have needed to modify your curves to deliver the same on plate dots that you were achieving with the old plate. It's the same amount of effort it takes in order to create new linearizing curves.

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  7. Most CtP devices can be set up to produce a linear plate with no curve. Yes it takes some work on the vendors part, and no you may not get exactly a 50 at the 50, but you can usually get to within 1% of linear. With regular maintenance and QC procedures you can keep a laser producing linear plates throughout its useful life. This can be done and still have the non print areas be "clear" and the dots made properly. We have done this to all of our CtP devices (around 12 of them). This eliminates the issue all together. We only apply 1 press curve (actually we have several press curves depending on stock, screening, press, and ink sets used), but only one curve is applied at a time. I have never seen a situation where a properly calibrated CtP device could not be made to image linear (or close to linear) plates. If this was the case i would consider a different plate or perhaps a different CtP manufacture. I do agree that even if the CtP device could not be made to produce linear plates that only one curve would be needed to produce the correct dot size on the plates. I am guessing that most people use two curves to make the math a little easier. If you have a curve that makes your plates linear, then a curve to make them have the desired dots for the press, you really only have to be concerned with the curve for the press, the "plate curve" would never really change, so effectively the operators only have to deal with one curve.

    Just some thoughts

    - CA

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