Knocked out in the shadows
As the image on the right demonstrates, unwanted white knockouts will appear in PDF documents with drop shadows if spots are converted to process. With Prinect Color Editor, it’s possible to pinpoint the problem by checking the colors and the overprinting properties of the objects in the PDF. In this example, an overprinting image with a CMYK value of 0% has been placed over a knockout spot color image in the “problem zone.”
Why does a background knockout occur if the overprinting object has no color and is therefore transparent? The answer lies in understanding what actually happens when a transparent object overprints. An overprinting CMYK image—whether colored or 0% “white”—knocks out every CMYK object underneath and leaves all spot color objects underneath untouched. If a spot color object is converted to CMYK, the CMYK object placed above cannot overprint the spot color.
The conversion of the spot color does not change the overprinting properties of the image placed above it. Thus the problem arises if the converted spots are overprinting or if they are overprinted by other objects. In a case like this, the user can correct the problem by building the drop shadow directly on the background.