PREPRESS
Knocked out in the shadows

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.