When creating a file that will be printed using a pre-press, it is necessary to turn on the
“overprint preview” mode. Go to View>Overprint Preview. It is also essential to use the “attributes” window to verify that overprinting fill or overprinting stroke is appropriately utilized.
In the above example, the upper left shows a CMYK mode of 0,0,0,100%, which does not entirely cover when combined with a partial background. (Attribute: overprint fill) However, the bottom right shows a CMYK mode of a combination of 74.61, 67.58, 66.8, 89.84%, or commonly referred to as registration black. Registration black covers the partial background without variations. (Attribute: overprint fill)
In the above example, a “trap” has been created. A trap occurs when a stroke is applied to the text and covers part of the background. First, create a knockout layer; define a background layer and a letter layer (which has outline type (Shift, CMD O).) Make two copies of the letter. Position the letter layer on top of the background layer. Select both layers and use the Pathfinder subtraction option to create a knockout.
Create the second letter layer with trap stroke; copy the same letter layer and add a stroke using 40% of text color and 100% of the background color. Position over background layer (Attribute: overprint fill)
In the above example, a “trap” has been applied partially to the background. Perform the same actions as in the “obvious trap” section except create a partial background. At the point when “creating the second copy of the letter layer,” – we are going to separate the stroke layer from the fill layer. Duplicate the letter layer and create a stroke layer by removing the fill. Modify the original letter layer by removing the stroke on the left side by adding anchor points where the background ends and later deleting the stroke in between.
The upper left example is a copy made in grayscale. Edit>Edit colors>Convert to Grayscale.
The above example shows what can occur when trapping is not utilized.
Sometimes the resulting color from the overprinting of two other colors is the desired effect, as two inks overlap to create a third color. Trapping (Knocking Out) would prevent the appearance of a third color.
In a Spread, the above object gets “knocked out” of the object below it, and the background color is brought into the knocked out area to ensure proper trapping.
Knock out without trapping will produce misregistration if printing is askew. Overprinting of the stroke would eliminate the misregistration.
The above example is self-explanatory. The top example displays Attributes>Overprint Fill. The bottom is an example of Attributes>Overprint Stroke.
In the past examples, we have shown how knockouts will emphasize text; however, the same is not valid for small text. The small text has a greater chance of misregistration, so overprinting is generally preferred.
In trapping cases involving smaller type, the eye can easily register changes in dark objects’ shape. To avoid the type appearing overly bold, shrink the background (choke). The left example displays Attributes>Overprint Fill and Overprint Stroke. The example on the right displays Attributes>Overprint Fill only.
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