Trapping

/ˈtræpɪŋ/

General Definition

This is a crucial operation in the prepress stage where two or more adjacent color areas sharing a common border are intelligently overlapped using a very thin stroke or bleed. The primary goal of trapping is to prevent the substrate's white material from becoming visible, or creating a slight gap along the color boundaries, which might occur due to slight material movement or minor, tiny errors in the printing press register (Register Error).

Real-World Usage

Understanding trapping is absolutely vital for graphic designers and prepress specialists. In designs where colored elements are placed exactly adjacent to one another without a border or overlap, even the slightest misalignment during plate transfer or printing leads to the unwanted appearance of the substrate's white material edges, severely degrading visual quality. Trapping automatically expands one color slightly underneath or over the adjacent color, establishing a small safety zone for overlap; this region is extremely small and barely noticeable under normal viewing conditions, but it effectively hides the print registration error.

Trapping settings can often be automated in specialized software such as Adobe Illustrator or advanced RIP processors like ESKO. However, comprehending parameters like trapping thickness and direction (Spreading or Pullback) remains critical, especially when combining background colors with lighter foreground colors. This is because the trapping thickness must be chosen carefully to exert the minimal possible impact on the final color composition where the colors meet.

Consultant's Note

Our consultant's advice is that trapping is mandatory and critical in Flexography due to the higher registration errors inherent to the elastic nature of polymer plates. In contrast, in Offset printing, trapping is less common and essential, mainly due to the higher precision of modern machinery and better register control. It is generally only utilized in highly register-sensitive projects or those involving Spot Colors, often to optimize production speed.

Although modern software typically handles trapping automatically, before submitting files to the lithography house, you must confirm that the trapping settings in the software align with the printing press's capacity and error type at the final destination. When using Spot Colors alongside CMYK process colors, manual trapping often yields the best results. This is because automated systems frequently fail to accurately calculate the complex interaction and blend required between spot and process inks.

Aligned with: ISO 12647 / Prepress Standards / ESKO Workflows