Is linear plates more important that backward compatibility with TVI curves?
Some will understand where the question comes from, but wanted to ask the community as a whole.
When targeting ISO or eg FOGRA 39 do you have linear CTP plates? Is it important? Are you able to hit the target TVI curves on paper? If you are having problems to get the TVI for FOGRA 39, would be interesting to know if a linear plate would be a better target for your workflow. If you had a linear plate what would be the ink coverage area of a 50% dot on plate once it came was printed.
A related question is of course what lpi are you ripping to?
Oh and one more question… do you know how to contact your national representative in the ISO technical groups (if you wanted to)?
Learning by teaching!
Constraining the standard to linear plates is idiotic. Nobody cares, or should care, about what the tones are on the plate. What's important are the requested tones in the file and the measured tones in the press work. The standard should identify the target press work tone reproduction (as it does the ink hues) and the printer should hit that tone reproduction curve by whatever means they choose. Ideally there would be only one target press curve irregardless of lpi, screening process, or, perhaps print process. One press tone curve to rule them all.
That would create a standard for print tone reproduction.
Linearizing plates is a pointless exercise. However, one should always verify that plates are being consistently imaged and developed. If your CtP+OLP aren't consistently imaging and developing plates you are screwed. We check a set of plates twice a week and every plate gets a control strip on it. If it were offered in an affordable and automated fashion I would push to have a control strip on every plate checked. If there are print abnormalities we can quickly identify/eliminate prepress and plating variables. We verify and log everything which has virtually eliminated press downtime, inaccuracies and inconsistency due to prepress.
Originally Posted by chevalier
In my opinion the plates should be linearized. It is easier to define where the problems come- from prepress, from ctp, or from the press. Otherwise we are in Catch 22- everybody says the problem is not in my machine.
Not true. Prepress sends plates with certain tone values to the press room. It does not matter whether the tone values are linear or not. What matters is the the tone values are consistent. If the plate measures the same (but not linear) as it did a month ago then any problem is likely not the plate but the press.
Originally Posted by ansoft
Also, if you say that plates should be linear irrespective of lpi, halftone screen type, process, or substrate then you will have poor alignment between print processes. You will also make certain screen types impossible to conform ( e.g. FM, high lpi AM/xm etc.) to any standard.
Last edited by gordo; 10-09-2012 at 12:37 AM.
Gordo I agree with you 100%. AS long as your plate is properly calibrated to hold the smallest dot you need every thing always falls in place. Have an exposure wedge in the gripper or tail of every plate and you will always know where you are at. With a correctly made curve if you must change exposure it doesn't matter the curve will move along with the exposure change to hold your smallest dot. We have been doing this with CTP since 1998 and never have had a curve problem
Originally Posted by gordo
Last edited by Green Printer; 10-09-2012 at 07:27 AM.
Only dot gain score on printed material is important. Most of time linerazition makes no sense. If plate causes huge dot gain on press with correct exposure (it can be negative plate) then pre-bending curve can help for smoothness on darker areas. Linerazition curve or any curve which pulls dot areas down on plate can be used as base for process calibration test.
I have never made PSO or G7 curves from a non-linear plate. It's hard to imagine a 50% dot being harder to control one way or the other. Currently I am not able to identify problems related to using linear plates, however in the past, when using a Fuji Saber (violet) I used to get strange negative dot gain in the highlights after a G7 set-up, particularly in the black channel; I never diagnosed the cause of that but always felt it was related to plate linearization. We print at 175 lpi. As a Rampage user I must use 25 fulcrum points so after setting up one CTP device and one press (lin+c+m+y+k) I am using 125 fulcrum points.
I understand the math simplicity argument for uncalibrated plates, however, a case can be made for whatever conditions require the least amount of correction would be best. Because I maintain curves for 4 platesetters and 14 curve sets and cannot identify a quality compromise with linear plates, my preference is for linear plates; otherwise I would have (4*14) 56 tone curves (or [56*25] 1400 fulcrum points) and each time I updated one set I would have to update three more.
In the US I would contact someone in the IDEAlliance Print Properties group who serves as a technical committee for ISO input for the print stuff.
Why worry about a 50% dot. You can swing an exposure on some ctp unit plus or minus 25% of exposure settings and still hold a perfect 50% dot while the highlights and shadows go to pot.