Adobe InDesign CS5 - Manual (Page 505)

499 USING INDESIGN
Trapping color
Last updated 11/16/2011
Adjusting ink options for trapping
Adjusting ink neutral density values
By adjusting the ink neutral density (ND) values that the selected trapping engine uses, you can determine the precise
placement of traps. The default ND values for process inks are based on the neutral density readings of process ink
swatches that conform to industry standards in different parts of the world. The language version determines which
standard it conforms to. For example, the ND values for the U.S. English and Canadian versions conform to the
Specifications for Web Offset Publications (SWOP) solid ink density values published by the Graphic Arts Technical
Foundation of North America. You can adjust process ink neutral densities to match printing industry standards in
other parts of the world.
The trapping engine derives the ND values for a spot color from its CMYK equivalent. For most spot colors, the ND
values of their CMYK equivalents are accurate enough for proper trap creation. Spot inks that aren’t easily simulated
using process inks, such as metallic inks and varnishes, may need their ND values adjusted so that the trapping engine
can trap them correctly. By typing new values, you can ensure that an ink that is observably darker or lighter is
recognized that way by the trapping engine; the appropriate trap placement is then applied automatically.
You can get the appropriate neutral density value for a given ink by asking your commercial printer. The most accurate
method of determining an ink’s ND value is by measuring a swatch of the ink with a commercial densitometer. Read
the “V” or visual density of the ink (don’t use process filters). If the value differs from the default setting, type the new
value in the ND text box.
Note: Changing the neutral density for a spot color affects only how that color will trap. It doesn’t change the appearance
of that color in your document.
Follow these guidelines when adjusting ND values:
Metallic and opaque inks Metallic inks are usually darker than their CMYK equivalents, while opaque inks obscure
any ink beneath them. In general, you should set the ND values for both metallic and opaque spot colors much higher
than their default values to ensure that these spot colors won’t spread.
Note: Setting an ink to Opaque or Opaque Ignore in the Type menu of the Ink Manager prevents an opaque ink from
spreading into other colors, unless another opaque ink has a higher ND value.
Pastel inks These inks are normally lighter than their process equivalents. You may want to set the ND value for these
inks lower than their default values to ensure that they spread into adjacent darker colors.
Other spot inks Some spot colors, such as turquoise or neon orange, are significantly darker or lighter than their
CMYK equivalents. You can determine whether this is the case by comparing printed swatches of the actual spot inks
to printed swatches of their CMYK equivalents. You can adjust the spot ink’s ND value higher or lower as necessary.
Customize trapping for specialty inks
Using certain inks involves special trapping considerations. For example, if you are using a varnish on your document,
you don’t want the varnish to affect trapping. However, if you’re overprinting certain areas with a completely opaque
ink, you don’t need to create traps for items underneath. Ink options are available for these situations. It’s usually best
not to change the default settings, unless your prepress service provider recommends changing them.
Note: The speciality inks and varnishes used in the document may have been created by mixing two spot inks or by mixing
a spot ink with one or more process inks.
1 Open the Ink Manager and select an ink that requires special treatment.