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Chapter 20. Output > To choose trapping preferences for a whole document:

To choose trapping preferences for a whole document:

1.
Choose Edit menu > Preferences > Document > Trapping folder tab (Ctrl-Shift-F12)

2.
From the Trapping Method drop-down menu, choose Absolute to use the trapping value entered in the Auto Amount or Indeterminate field. The Auto Amount value is used if the foreground color is on top of a flat color. The Indeterminate value is used if the foreground color is on top of multiple shades or colors or over an imported picture. When the object color is darker, the background color chokes into the object color by the Auto Amount. When the foreground object color is lighter, the object color spreads into the background color by the Auto Amount.

or

Choose Proportional to use the trapping value entered in the Auto Amount field, multiplied by the difference in luminosity (lights and darks) between the foreground object color and the background color. The width of the trap will vary and be determined by multiplying the Auto Amount value by the difference in luminosity between the object and background colors.

or

Choose Knockout All to turn trapping off for all objects. Objects will print with 0 trapping

3.
Choose On or Off from the Process Trapping drop-down menu. With Process Trapping on, each process component (cyan, magenta, yellow, and black) is spread or choked depending which is darker—the foreground object or the background color. For example, if the cyan in the foreground object color is lighter than the cyan in the background color, the foreground object cyan is spread into the background cyan—but only on the cyan plate.

The trap width is equal to half the Auto Amount value when Absolute trapping is specified. When Proportional trapping is specified, the amount of trap is the Auto Amount value multiplied by the difference in luminosity values between the foreground object and background colors.

When Process Trapping is off, all process components trap by the same amount and use the trapping settings for those colors, as determined in the Colors > Edit Trap area.

4.
Enter a trapping value in the Auto Amount field or choose Overprint from the drop-down menu. Either the value entered or the Overprint setting will be used in the Trap Specifications dialog box (Edit menu > Colors > Edit Trap) and on the Trap Information palette whenever a field in either of these two locations is set to Auto Amount (+/-).

5.
Enter a trapping value in the Indeterminate field or choose Overprint from the drop-down menu. If a foreground object is over a background that consists of multiple shades or colors or is over an imported picture, either the value you entered or the Overprint setting will be used.

6.
Enter a percentage value in the Knockout Limit field to set the luminosity (light and dark) value limit at which a foreground object color knocks out the background color. The luminosity value is the percentage difference in luminosity between the foreground object color and the background color.

7.
Enter a value in the Overprint Limit field This value sets the shade percentage limit below which the foreground object color will not overprint the background color. For example, if the Overprint Limit is set to 92%, a foreground object colored with a black value of 85% will not overprint, even if that color or object is set to overprint (via the Edit Trap > Trap Specifications dialog box). The object will trap using the value in the Auto Amount field.

An Overprint setting chosen on the Trap Information palette will cause the selected object to overprint, regardless of the current trap settings or any Overprint Limit value entered in any other dialog box.

8.
Leave the Ignore White box checked to turn off trapping for any instance in which the foreground object color is on top of white and other color areas in the background. This is the preferred situation, since the white area won't be considered when the trap is calculated for the other colors.

When this box is unchecked, all objects on a white background will overprint. If an object is set to spread over a background color, then the Indeterminate value will be used for the spread.

9.
Click OK to close the Document Preferences dialog box.

The Trap Specifications dialog box controls trapping on a color-by-color basis. The default settings for each color display and can be modified using this dialog box.


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