PDF Ground Controls Categories – Trapping
Trapping Ground Controls categories for Portable Document Format files are in the PDF Ground Controls area in FlightCheck preflight software by Markzware.
DEFINING THE PDF GROUND CONTROL CATEGORIES: TRAPPING
Trapping is a printing term used to describe the process that eliminates misregistration of color plates. Printing presses move swiftly, causing color plates to shift slightly. If you have seen newspaper comics where the yellow plate falls short of a black border, you have seen misregistration. Colors can be trapped to either spread (grow larger) or choke (become smaller) to compensate for gaps between colors that should touch each other when printed.
It is always best to let printing professionals apply traps on their equipment since trapping rules can change, depending on the type of project. For instance, if the project is packaging, glues and various paper stock can require special traps.
TEXT
When type prints in a small size, it is necessary to adjust traps carefully so they do not interfere with originally intended shapes of the typeface.
Overprint:
One method to eliminate trapping is to set colors to overprint so that the colors that overlap each other mix inks during printing. This forces the top color to overprint all colors beneath it. Black text is set to overprint by default. (Ex. A picture may have black text in a caption that is on top of an image. The text color will cover and mix with the colors in the image beneath it.)
Knockout:
Depending on the size of color shapes that overlap during printing, some shapes on top can be set to “knock out” all underlying colors, so that colors beneath the top color shape do not print. Only the top-most color shape prints. For instance, if text is set to knockout, it acts like a cookie cutter and cuts out all color beneath the text, so that the text color prints directly on the paper color. If text is made up of more than one CMYK component value and is small, any misalignment during a press run will show as a halo of color.
TEXT USING COLOR
Traditional traps are set for White to knockout and set Black to overprint. Other combinations can result in bad trapping, or may be required for specialty printing such as packaging, etc.
________Not Set to Knockout:
White is not set to knockout by default. In this field you can type a color such as White. It is important to identify this type of trap since the other colors used in the art may shift into the white area, creating an undesirable halo of color.
Text Using Color
________Not Set to Overprint:
Black is not set to overprint by default. In this field, you type a color such as Black, so that Black text will not overprint when it meets the settings entered below.
Ignoring text larger than ________ points:
In this field, type a number for the overprint to occur below a particular point size. Smaller type needs to overprint, but larger type is better suited for traditional traps.
BACKGROUND
It is crucial to use correct trapping of especially large areas of background colors or images. As the printing press moves the paper and rapidly spreads ink, shifts can occur that result in unsightly gaps.
Overprint:
Set the top color to print and mix with colors underneath. An example of where overprinting text can be problematic is when there is a large area of black with only a partial image overlap set to overprint. The overlapping area will print with a rich black on the small overlapping shape due to the blending of the inks in the image, causing it to stand out compared to the section of the black shape that does not overlap. Large black concentrated shapes are sometimes better suited to traditional trapping. Spot colors can be set to overprint in order to achieve a rich color.
Knockout:
Set the top color to cut or drop the colors underneath. Areas that are set to knockout the color underneath are normally paired with a trap compensation of spread or choke to eliminate misregistration.
FRAME / LINE
Small lines can cause trapping issues that are similar to trapping small text to backgrounds. These checks are important since the objects will not be seen easily due to their size.
Overprint:
Set the top line color to mix with the colors underneath when printing. This is a standard setting to avoid small line traps.
Knockout:
Set the top color to cut or drop the colors underneath. Areas that are set to knockout the color underneath are normally paired with a trap compensation of spread or choke to eliminate misregistration.
