Color Trapping is a major aspect in the
apparel decorating (screen printing) industry as well as any printing
industry for that matter. Most artists supplying designs to screen
printers are expected to supply accurate color separations utilizing
chokes and spreads (traps). Color Trapping is the spreading,
overprinting or under cutting of objects in order to prevent printing
inaccuracies such as registration issues. One of the most widely seen
issues in the textile screen printing industry is the poor registration
where the white underbase (white printer for dark shirt printing) is
visible where it should not be visible.
Understanding Color Trapping and the various
methods to utilize them will ensure your prints are correct along with
ease of setup and in many cases will speed up the overall production.
Trapping and Overprinting can be set in multiple ways within CorelDRAW; directly in your document with each object, on the
Separations Tab in the
Document Overprints dropdown list or by using the
Automatic Trapping option in the print dialog. See your CorelDRAW User Guide for more information on Color Trapping.
The basic methods for Trapping are Overprint,
Choke and Spread. Note: Spread is generally described as Trapping in
the apparel decorating industry.
- Overprint is where one object or color prints directly over another.
- Spread (Trapping) is where a thin line
(outline) is added to the edges of the objects where the object is cut
out of the underlying object. The spread overprints the underlying
objects. Essentially, an outline is added to the top object to make it
larger.
- Choke is where the underlying object is
given a small outline so that the top object overprints the underlying
object or color. Essentially, the bottom object is given an outline so
that it prints larger than the original object.
Manually setting Traps on objects when
designing can ensure an accurate separation for your screen printer.
Sometimes you may forget to add traps when designing and a global choke
and spread size may not work due to varying sized elements in your
design. This is when manual color separations and trapping are needed.
Small type with serifs may not allow a .5 choke while other elements in
the design warrant a .75 choke or trap.
Fig 3 shows a side view of a
Butt registered element where the colors or objects are exactly the
same on top of each other. The Spread or Trap shows where the top color
has an outline to make the top color slightly larger than the bottom or
underlying color and a Choke where the underlying color has a white
outline to make it slightly smaller than the top color or object.
The following steps will show you how to
apply Chokes and Traps to a manual separation in CorelDRAW. In this
design, we will be adding Chokes and Traps to a simple spot color design
that will be printed on dark t-shirts where a white underbase (white
printer) is needed yet
NO white is supposed to show in the print.
Step1: Create your design and size it to final print size.
Step2: Add registrations marks and labels (ink colors)
Step3: Duplicate your design for each color to be printed or copy and paste to a new page for each color to be printed.
Step4: Convert each color plate to Black & White or Grayscale if halftones are used in the design.
Step5:
- Apply a white outline to all objects on the white plate (white printer or separation). This will make the white slightly smaller so the top colors cover all of the white underbase. This is also referred to as Choking.
- Apply a black outline to the top colors (plates or separations)
In some instances, you may only be able to
apply one or the other, Choke or Trap, due to the object properties or
how the objects are stacked in the design. Practice, printing equipment
and the inks used will also play a role in dictating which method is
used or if both Chokes and Traps are warranted. Basically, some R&D
and trial and error will turn anyone into a good color separator.
In the diagram below, it shows the outlines
in the color of the actual plate. For the manual separations you would
use black or white outlines for your Traps or Chokes.
Step6: Print your separations to film knowing the final print will look as expected and there should be no issues with registration.
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