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Trapping

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Learn how to trap color between objects and trapping options in Illustrator.

Where colors printed from separate plates overlap or adjoin one another, incorrect registration by the printer can cause gaps between colors on the final output. You can use a Trap (a small area of overlap between colors) to compensate for potential gaps between colors in your artwork.

There are two types of traps:

Spread: A lighter object overlaps a darker background and seems to expand into the background.
Choke: A lighter background overlaps a darker object that falls within the background and seems to squeeze or reduce the object.

Create a trap

The Trap option creates traps for simple objects. It identifies the lighter-colored artwork (object or background) and overprints (trapping) it into the darker artwork. Apply the Trap option from the Pathfinder panel or as an effect, and alter the settings at any time.

Ensure your artwork is in CMYK color.

If your artwork is in RGB mode, go to File > Document Color Mode > CMYK Color.
Select two or more objects.
Follow any of these options:
- To apply the command directly to the objects, go to Window > Pathfinder. Select Trap from the panel menu.
- To apply the command as an effect, go to Effect > Pathfinder >Trap. Select Preview if you want to preview the effect.
Set trap options, and select OK.

A. Area of overprinting B. Area of knockout C. Background color D. Foreground color

Trap options

Thickness	Specifies a stroke width between 0.01 and 5000 points. Check with your print shop to determine what value to use.
Height/Width	Specifies the trap on horizontal lines as a percentage of the trap on vertical lines. Specifying different horizontal and vertical trap values lets you compensate for on‑press irregularities, such as paper stretch. Contact your print shop for help in determining this value. The default value of 100% results in the same trap width on horizontal lines and on vertical lines. To increase the trap thickness on horizontal lines without changing the vertical trap, set the Height/Width value to greater than 100%. To decrease the trap thickness on horizontal lines without changing the vertical trap, set the Height/Width value to less than 100%.
Tint Reduction	Reduces the tint of the lighter color being trapped; the darker color remains at 100%. This option is useful when trapping two light-colored objects, where the trap line may show through the darker of the two colors, resulting in an unsightly dark border. For example, if you trap a light yellow object into a light blue object, a bright green border is visible where the trap is created. Check with your print shop to find out what percentage of tint is most appropriate given the type of press, inks, paper stock, and so on being used.
Traps With Process Color	Converts spot-color traps to equivalent process colors. This option creates an object of the lighter of the spot colors and overprints it.
Reverse Traps	Traps darker colors into lighter colors. This option does not work with rich black—that is, black that contains additional CMY inks.
Precision (as effect only)	Affects how precisely an object's path is calculated. The more precise the calculation, the more accurate the drawing and the more time is required to generate the resulting path.
Remove Redundant Points (as effect only)	Removes unnecessary points.

Create a spread or choke

For more precise control of trapping and for trapping complex objects, you can create the effect of a trap by stroking an object and setting the stroke to overprint.

Select the topmost object of the two objects that must trap into each other.
In the Stroke box in the Tools panel or the Color panel, follow any of these options:
- To create a spread, enter the same color values for the Stroke as in the Fill.
- To create a choke, enter the same color values for the Stroke as in the lighter background. Here, the Stroke and Fill values will differ.
Go to Window > Stroke.
Enter a stroke width between 0.01 and 1000 points for the Weight option.

Your trap value is half of the stroke width value. Check with your print shop to determine the stroke width.
Go to Window > Attributes.
Check Overprint Stroke or Overprint Fill.

A. Overprinted stroke creates choke trap B. Fill creates knockout C. Area of trap D. Area of knockout

Trap a line

Select the line to be trapped.
In the Stroke box in the Tools panel or the Color panel, assign the stroke a color of white.
In the Stroke panel, select the desired line weight.
Copy the line, and choose Edit >Paste In Front. The copy is used to create a trap.
In the Stroke box in the Tools panel or the Color panel, stroke the copy with the desired color.
In the Stroke panel, choose a line weight that is wider than the bottom line.
Choose Window > Attributes.
Select Overprint Stroke for the top line.

A. Overprinted top stroke creates spread trap B. Bottom stroke creates knockout C. Area of knockout D. Area of trap

Trap a portion of an object

Draw a line along the edge or edges that you want to trap. If the object is complex, use the Direct Selection tool to select the edges to be trapped, copy them, and choose Edit > Paste In Front to paste the copy directly on top of the original.
In the Stroke box in the Tools panel or the Color panel, select a color value for the Stroke to create either a spread or a choke.
Choose Window > Attributes.
Select Overprint Stroke.

Drop shadow with a trap (left) is based on the line drawn where the object and its drop shadow meet (right).

Tips and tricks

Trapping isn't necessary for overlapping painted objects with a common color, creating an automatic trap.
Don't apply mixed process colors or tints of process colors to text (type) at small point sizes, as any incorrect registration can make the text difficult to read.
Trapping text at small point sizes can result in hard-to-read text. As with tint reduction, check with your print shop before trapping such text. For example, if you're printing black text on a colored background, just overprint the text onto the background.
In cases where the top and bottom objects have similar color densities, and none of the colors is darker than the other, the Trap option determines the trap based on slight color differences.
You can use the Reverse Trap option if the trap specified by the Trap dialog box isn't satisfactory.

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