You can use a separate, dedicated trapping program to create traps automatically, or you can use Illustrator to create traps manually. Overprint black ink to aid in registration. Overprinting black can prevent gaps from appearing between black and colored areas of your artwork. Overprint when the artwork does not share common ink colors and you want to create a trap or overlaid ink effects.
When overprinting process color mixes or custom colors that do not share common ink colors, the overprint color is added to the background color. You should also carefully check overprinted colors on separated artwork using integral proofs where each separation is shown in register on a single piece of paper or overlay proofs where the separations are shown in register on separate plastic sheets stacked on top of each other. Consult with your print shop about the exact percentages of color to add to the black.
To overprint all black in your artwork, select the Overprint Black option in the Print dialog box when you create color separations. This option works on all objects that have black applied through the K color channel. However, it does not work for objects that appear black because of their transparency settings or graphic styles.
You can also use the Overprint Black command to set up overprinting for objects that contain a specific percentage of black. OPM has an effect only if OV is on. If OV is OFF, then every object that is painted removes any previously painted color in the same area as can be seen in the topmost image. That means if a CMYK object is painted, any previously painted objects in CMYK would be knocked out, but previously painted spot color objects would be overprinted.
The same would work the other way around, when spot color overprints CMYK. Both are shown in the two images in the middle. That means the Cyan text knocks out every previously painted Cyan objects but previously painted Yellow and Magenta or Black remains is overprinted as can be seen in the image at the bottom.
This actually has surprising results in some cases: ICC based color conversion Assume that the cyan text above would be color converted to match the color space of the printing machine using ICC based color conversion. In many cases the result would then also use small amounts of Yellow plus Magenta and Black.
This means that all of a sudden it would not overprint the underlying yellow box anymore but would knockout even if OPM is ON. The result would be very similar to the two images at the top. I suspect in these days when digital printing machines - which don't even know what a spot color is - take over much of the total print volume, conversion to CMYK is the sad end of most spot colors. Luckily overprinting spot colors are rarely used, however Even more surprising is this effect when it occurs after transparency flattening.
Why is that? Overprint is frequently used by transparency flattening engines. This makes a lot of sense for spot colors since - as we have seen - they can easily overprint most other objects. However, when then the spot colors are converted to CMYK every such objects knock out any underlying objects. And that in many cases changes the appearance of the whole page dramatically which has caused lots of confusion and production problems.
Dietrich von Seggern callas software GmbH. It has a overprint effect in it but I can't figure out a way to export it as a tif or jpg with a simulated overprint. Neither export has a simulate overprint option, and both export with a big green blob on top of everything the green blob is the shape that is overprinting Save as PDF, press ready, defaults to view of green blob not simulated overprinting Save as PDF, change to PDF 1.
Same result as above. If the Discard White Overprint option is not selected in the Document Setup dialog, it can be overridden by selecting the option in the Print dialog. In this scenario the appearance attributes of previously selected objects is copied to the new object, resulting in overprint applied to the white-filled object.
A non-white object with overprint is changed to an object with white fill. To overcome this problem, we now remove the overprint attribute from white objects during operations like printing or saving to EPS or PDF. This enables users to use print and output without the need to check and correct for white-object overprint in artwork. This approach will be optimal for most scenarios - legacy artwork, new artwork, non-White objects with Overprint applied to them when changed to White.
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