When The Washington Post NewsArt department shifted over from Freehand MXa to Illustrator CS2 in 2007 we started experiencing reproduction problems associated with white-overprints and rich-black. When this results in a million confused readers, this can be a major headache.
Example Problem Graphic – Where are the white (reverse) numbers in the bar chart?
Fixed Graphic – Note white numbers in bar chart on the right.
Under most situations white should NOT overprint (cereal boxes are one exception where there is actually a white ink) but knockout (cut thru) the colors below showing the “white” paper as absence of ink. Rich-black is useful when creating a very deeply hued black like on some page backgrounds in the National Geographic Atlas of the World, 8th Edition (rich blue black there) but otherwise can create registration problems on the printing press (e.g.: rich “black” type becomes blurry when misregistered).
TIP: Mordy Golding of Real World Illustrator! has a good post on white overprints on his blog there.
It turns out that Freehand would not allow white to be overprinted (the overprint check box would be auto dimmed when fill or stroke were set to white). And it never had rich-black problems.
Illustrator will display a warning dialog when setting an white fill or stroke to overprint. And it will display a little (!) icon in the Attributes panel when it thinks you might not want to be overprinting white. But it does not alert when changing, say, a black filled, overprinting object to white filled. Instead, the object effectively disappears. Bad news!
Warning Dialog – When setting white fill or stroke to overprint. But does not display when changing the fill or stroke to white when overprinting has already been enabled.
Alert Icon in Attributes Panel – When Illustrator detects you’ve set an object to white-overprint it shows a little yellow (!) icon next to the overprint checkboxes. But 99% of Illustrator users have never even heard of the Attributes panel.
Charts originating in Microsoft Excel are one typical culprit for rich-black. Started a document in RGB mode and then switching it to CMYK is another. Unfortunately, rich-black can creep in whenever color modes are being converted so pay attention to those dialogs and check your “gray” and “black” objects to make sure the have good (K only) values.
What is the best practice in Illustrator?
There are several plugins that help mitigate these major bugs.
The first is a simple white-overprint check plugin from Doug @ Worker72a. There are free and pay (cheap) versions. Each time Illustrator opens a file it will display an alert if a white-overprint error was found. But this plugin doesn’t fix the problem. There is no solution for detecting rich-black problems except manually checking your document or examining a high-end separations proof.
Once you have determined a white-overprint problem exists, you can either hunt thru all your page object manually or buy another plugin from Doug called WhiteOP2KO that will automatically search all objects and fix their overprint status.
However, I prefer another plugin solution to fix white-overprint from Nick at Astute Graphics. His PhantasmCS plugin will both remove the white-overprints and look for and fix pure rich-black problems (100% K). It will not fix 50% or other shades of rich-black but will take care of 95% of the rich-black problem. Run any of the PhantasmCS plugins with the default “0″ settings but with “Rich Black to Pure Black” and “Remove Overprint when White” options enabled.
Perhaps a future version of Illustrator will fix these serious bugs. Until then, these are the workarounds.