At my old shop we used to linearize first, then apply press curves.
Was there any discussion or reasoning done behind the decision to linearize first then apply press curves or was it done because it seemed like the right thing to do?
gordon p
the linearising of the plate is to bring the exposure and development to standard levels.as the exposure ie the laser power and development ie the strength,temp,dwelltime of plate and the coating of the plate are variables.linearisation is done biweekly at our place to ensure the exp/dev is under control.
Since this is a very fundamental, technical, prepress workflow question I would have thought that the results would have been strongly skewed to favor one of the two options rather than evenly split (so far).
It would be great if some of the vendors (Steve M, Kevin C, etc.) or their technical specialists (I know you watch this forum) would also cast a vote for which approach they suggest.
I find that the comments in the posts so far have been excellent and provide much food for thought.
best, gordon p
I have no experience in this area but in general it seems to me that starting from a linear condition would be better. Practically speaking for this situation it probably does not matter since many seem to do just fine without linearization.
My view is that there is only one linear curve but an infinite number of nonlinear curves. I hope I am understanding this discussion. I am assuming that by linear one means that if the plate imaging system is told to make a 50% dot for example, the result is a 50% dot on the plate.
I'll try and clarify.
Back in the day, in a film workflow, the process was to linearize the film output. I.e. Ask for 50% in the file and then measure 50% in the film (and supposedly the same correspondence would occur through the tone scale. Nobody measured what the dot size on the plate was. Linear film was the accepted file interchange format. Very few prepress shops would put a curve in the film to compensate for differences in dot gain on press.
Along comes CtP.
You now have the option to apply curves to the plates to compensate for differences in dot gain on press due to a variety of issues - paper choice, screening choice, press condition, etc. I.e. By not sending a linear plate to the press room you can "normalize" or "optimize" the plate for the given press condition.
So, you can have a "plate curve" and a "press curve."
The plate curve can be its natural (uncalibrated state). For example. With "X" CtP device and plate combination 50% in the file becomes 45% on the plate and 25% in the file becomes 32% on the plate. The plate has an inherent curve that is not linear.
A press curve could be used in order, for example, to make my 20 micron FM (which has a high dot gain) tonally match my 133 lpi AM which has a low dot gain. In that case I might want the requested 50% in the file to create a 35% dot on the plate in order to achieve a final tone of 68% in the presswork. I.e. both my FM and AM produce the same final tone on press from a given requested tone value.
So, the options are to:
1) First apply a linear "plate curve" so that requested tones in the file generate the same tone value on the plate. Then apply a "press curve" to create the needed tones on the plate to achieve the tone response I want on the press sheet. Note that if I need a linear plate in order to achieve my on press tone goals then the linearizing plate curve is also the press curve.
or
2) Accept the natural non-linear plate response and make that the base line. I would then only apply a press curve to the nonlinear (uncalibrated via plate curves) plate to achieve my on press tone objectives. The requirement is that the non-linear plate response is consistent. I.e. whenever I ask for a 50% tone I get a 45% on the plate.
best, gordon p
Thanks Gordon, I think I follow the steps.
In option 2, if one put a control strip on the plate to be used to determine that the imaging of the plate is correct and this control strip was made of gray scale screens such as 5%, 10%, 20%.... 90%, 100%, would one expect that they measure as the non linear values of the plate curve?
A question about the curve. Is the curve above true for all angles and all rasters? Or would you have a series of plate curves, for each angle and each raster ay each resolution?
If the deviation is due to the problem of dots being digital as opposed to analogue then a "curve" would be a missrepresentation, a scatter graph would be more accurate, but ofcourse harder to apply. I guess what I am saying is that even if I can see that a perfect linearisation would perhapps be an advantage. The potential errors and the complexity of keeping all the variables without error and atune to the processs seem impractical.
So even if it is not a perfect bell curve, at least with the combination of plates and raster we use it is reasonable to consider the deviation from the bell curve negligible (ie less than the deviation by imperfect readings).
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