Mastering trapping techniques in design
One of the most effective methods for correcting registration errors in printing is the use of trapping. By creating a thin stroke around graphic elements, trapping prevents the appearance of white gaps between colors in the underlying layers. This stroke is very thin and is mandatory for printing processes like flexography, where the plastic material is flexible and the machine runs at high speeds.
Unlike overprint technique, trapping does not affect the fill color of an object; it only creates a halo or trap around the selected element. The stroke applied to the object is typically around 0.3 points thick, so it has minimal impact on the overall graphic design. However, its use is essential, especially in flexographic printing due to the nature of the production process. In offset printing, trapping is less common due to the slower machine speed and the use of paper and board materials, which offer more control than plastic.
Like overprinting, trapping is used to prevent visible white gaps in the underlying layer. However, overprinting alters the color of the object by blending it with the background, which is not always feasible. Generally, overprinting is more commonly used for black elements, while trapping is used for colored elements.
The Trapping Process
Creating a halo or trap around objects is not as simple as most designers might think. In the broadest definition of trapping, a thin stroke must be defined with an overprint for each object. However, this stroke can have its own direction and color. For example, the thickness can vary from 0.3 points inward, outward, or to the middle, depending on the requirements, and the direction can be chosen based on the background color and object color. Additionally, it is incorrect to always use a black overprint for the stroke; in some cases, the trap should also be defined in color.
In general, you can apply a stroke to elements such as text, illustrations, and other graphic objects, and define it as an overprint in software like Illustrator or CorelDRAW. Note that the overlap only applies to the stroke, and the fill color of the object remains unchanged. Until you gain sufficient skill in trapping, it is best to use only black for the trap.
Specialized Trapping Software
While you can use Illustrator or CorelDRAW to create traps, this process can be time-consuming and tedious for a large number of objects, and it can be difficult to maintain accuracy and make adjustments during preflight. This is where specialized plugins like Esko Deskpack come in handy.
This software can automatically select all objects in a file and apply trapping in manual, semi-automatic, or fully automatic modes. Esko is so powerful that it can even define the direction and color of the stroke in the best possible way. Using the Esko plugin in Illustrator is particularly useful because you can even create traps for pixel-based images.
Ultimately, trapping, like overprinting, does not completely eliminate registration errors during printing. The white gap under the object will still exist, but it will be hidden by the stroke. The standard thickness of 0.3 points is common, but it can be reduced to 0.2 points in some cases. Trapping is mandatory for flexographic printing and can be applied using specialized software like Esko instead of graphic design software.
