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Adobe ACROBAT X PRO Manual

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USING ACROBAT X PRO
Print production tools
Last updated 10/11/2011
About trapping black
When creating or editing presets, the value you type for Black Color determines what is considered solid black and rich
black. A rich black is any black color that uses a support screen—additional percentages of one or more process inks to
strengthen the black.
The Black Color setting is useful when you must compensate for extreme dot gain (as when using low-grade paper
stock). These situations cause black percentages lower than 100% to print as solid areas. By screening back blacks or
rich blacks (using tints of solid black) and decreasing the Black Color setting from its default of 100%, you can
compensate for dot gain and ensure that the trapping engine will apply the proper trap width and placement to black
objects.
When a color reaches the Black Color value, the Black trap width value is applied to all abutting colors, and keepaway
traps are applied to rich black areas using the Black trap width value.
If support screens extend all the way to the edge of a black area, any misregistration causes the edges of support screens
to become visible, creating an unwanted halo or distorting the edges of objects. The trapping engine uses a keepaway,
or a holdback, for rich blacks to keep support screens a specified distance away from edges of reversed-out or light
elements in the foreground, so that the light elements retain their sharpness. You control the distance of support
screens from the edges of black areas by specifying the Black trap width value.
Note: If the element you’re trapping is a thin element, such as a black keyline around graphics, the trapping engine
overrides the Black trap width setting and limits the trap to half the width of the thin element.
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.
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