We are in a production environment and have to trap files all the time. Normally it's not an issue but I've noticed my staff are having problems with overprinting colors. I don't know if this is a document setting or preferences problem, or something resulting from a recent update. I am currently running Illustrator CS5.5 (15.1.0 and have all the latest updates).
Here is how to reproduce my problem:
create a (blue) box using the following color: C100, M20, Y0, K0
Overlapping the blue box, create a (magenta) box with this color: C0, M100, Y50, K0
Use the same color for the stroke.
On the magenta box, turn on overprint preview, and enable "overprint stroke".
You will see that the stroke becomes semi-transparent as a simulation of how it will print when the stroke overprints. This is how it should normally work.
Now try this:
Change the stroke on the magenta box from C0, M100, Y50, K0 to C1, M100, Y50, K0 (in other words, change the cyan from zero to 1)
The overprint/trapping disappears entirely!
This happens with other colors as well, and the common denominator seems to be that the overprint fails the moment that any 100% color UNDERNEATH the overprinting stroke is present in the stroke color.
Without the overprint working, we are stuck manually creating stroke intersection objects and jumping through all kinds of hoops where we shouldn't have to.
If there is a setting I've missed or a workaround, please help!!!
Hi Monika. I don't understand what you mean? To me overprint means that the object underneath is NOT masked out by the object above.
I was just on a support call with Adobe and they recognized the problem. we thought we had fixed the problem by trashing the Illustrator prefs but it was premature - we changed the fill not the stroke.
I will attach some screen shots.
This is often hard o explain but since you have a cyan plate then added a precentage to the Magenta the precentage of 1% is process the Cyan plate only runs once through the press and therefore you canot over print sice it makes up a component of the magenta.
The means that the are where the 1% cyan is will separte onto the the cyan plate wjhich can only run once.
Say you sue only two fills and the magenta had a 5% C the cyan plate would look like this
The Magenta plate would loo like this
So thee is no way to overprint it since is is already overprint by being processed so it is doing what it is supposed to do. And of course you cannot6 have 101% Cyan unless you runb it twice.
Multiply is one wa of doing it but not necessarily the best way, the best way would be to run the cyan and magenta mix as spot colors.
There are other ways as well but time consuming so you may not want to even try to accomplish this.Not sure what you would gain with 1% C?
Overprinting in Illustrator works like this:
Wherever the underlying object(s) and the overprinting object both have any non-zero value of a given component ink, the overprinting object's value for that ink overrides the underlying object(s) value for that ink. (As implemented, the setting would more accurately be labeled "override" instead of "overprint".)
For example, if the overprinting object has a M value of 20%, and the underlying object has a M value of 40%, the M separation plate will not show 60%; it will be 20%.
This is, of course, quite counter-intuitive to anyone who has actually had ink under his fingernails. So I hear your logic, and have long argued the same for many years: Overprinting is supposed to mean exactly the opposite of knocking out, but that is what you get on a sep plate of an ink for which both the objects have values. The rationalization of the behavior is that it is necessary to accomodate the fact that a single separation plate cannot carry more than 100% of a given ink. In other words, it's as if PostScript has never heard of a double-hit or second-pass on press, or a double-burn on a plate, all of which were commonplace in pre-computer offset printing.
So the workaround is to set the overprinting object to the Multiply transparency mode. This does not, in fact, always yield exactly the same thing as would real-world overprinting (double-hit or second-pass), but the resulting appearance is usually an acceptable approximation, given only one sep plate per ink in the program's separation output.
I wonder about any of this stuff being well thought out!
After all you can easily run another cymk set of inks as spot colors. There may be som odd ball reason on very rare occasions where you would print a pocess image over another image but besides that scenario running a cmyk set as spot colors takes care of running the form through twice.
Doublke or triple burning a plate is only going to get you 100% of a color for that plate.
I just wonder about all of this convoluted verbage.
I found a usable workaround in another thread. It's a bit cumbersome, but will suffice for now.
Ideally, Illustrator would (at least optionally) treat all overprints this way.
In order to maintain an overprint effect, a copy of the purple object is duplicated beneath the original one. It doesn't matter if the stroke is set to overprint. Instead, set the layer's transparency mode to darken.
Screen shot attached.
You still clearly do not understand why this would bnot be physically possible with an over print.
Your work around in theis case works but in some cases it might not produce the desired result multip[ly is more likely to produce the desired result.
Overprint should not work this way as it is not possible on a cmyk job.
Mukltiply works when you esetailly want to mix the screens wwhich is not over print it in essence creates a new shape with an entirely new color made up of the colors you were using.
It does not make a color that is more than 100% C mixed with the other color it just makes a color composed through and eqaution to produce something visual that staisfies that eqquation.
It looks right to visually and will print that way but it cannot exist a a four color cmyk process print job.
Not to say that you have not acheived wht you want but it was clearly pointed out to you my Monikaa's first posting.
It is not an overprint problem, overprint is work as it should.