Bedienungsanleitung Adobe ACROBAT DC - 2015 (Seite 495 von 538) (Englisch)

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Print production tools (Acrobat Pro DC)

Last updated 4/7/2015

Trap 1-Bit Images Ensures that 1-bit images trap to abutting objects. This option doesn’t use the Image Trap Placement

settings, because 1-bit images use only one color. In most cases, leave this option selected. In some cases, such as with

1-bit images where pixels are widely spaced, selecting this option may darken the image and slow the trapping.

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.

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