Adobe Acrobat XI User Manual download pdf (Page 546)

539

Print production tools (Acrobat Pro)

Last updated 1/14/2015

Black Density Indicates the neutral density value at or above which InDesign considers an ink to be black. For example,

if you want a dark spot ink to use the Black trap width setting, enter the neutral density value here. This value is typically

set near the default of 1.6.

Sliding Trap Determines when the trapping engine starts to straddle the centerline of the color boundary. The value

refers to the proportion of the lighter color’s neutral density value to a darker, abutting color’s neutral density value. For

example, setting the Sliding Trap value to 70% moves the point at which the trap begins to straddle the centerline to

where the lighter color exceeds 70% of the darker color in neutral density (lighter color’s neutral density divided by

darker color’s neutral density > 0.70). Colors of identical neutral density will always have their traps exactly straddle the

centerline, unless the Sliding Trap is set to 100%.

Trap Color Reduction Indicates the degree to which components from abutting colors are used to reduce the trap color.

This setting is useful for preventing certain abutting colors (such as pastels) from making an unsightly trap that is

darker than either color. Specifying a Trap Color Reduction lower than 100% begins to lighten the color of the trap; a

Trap Color Reduction value of 0% makes a trap with a neutral density equal to the neutral density of the darker color.

Trapping imported graphics

You can create a trap preset to control traps within images, and to control traps between bitmap images (such as

photographs and those saved in raster PDF files) and vector objects (such as those from a drawing program and vector

PDF files). Each trapping engine handles imported graphics differently. It’s important to be aware of these differences

when setting trapping options.

Trap Placement Provides options for determining where the trap falls when you trap vector objects (including objects

drawn in InDesign) to bitmap images. All options except Neutral Density create a visually consistent edge. Center

creates a trap that straddles the edge between objects and images. Choke causes objects to overlap the abutting image.

Neutral Density applies the same trapping rules as used elsewhere in the document. Trapping an object to a photograph

with the Neutral Density setting can result in noticeably uneven edges as the trap moves from one side of the edge to

another. Spread causes the bitmap image to overlap the abutting object.

Trap Objects To Images Ensures that vector objects (such as frames used as keylines) trap to images, using the Trap

Placement settings. If vector objects don’t overlap images in a trapping page range, consider turning this option off to

speed trapping of that page range.

Trap Images To Images Turns on trapping along the boundary of overlapping or abutting bitmap images. This feature

is on by default.

Trap Images Internally Turns on trapping among colors within each individual bitmap image (not just where they

touch vector artwork and text). Use this option only for page ranges containing simple, high-contrast images, such as

screen shots or cartoons. Leave it unselected for continuous-tone and other complicated images, as it will create bad

traps. Trapping is faster when this option is unselected.

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.

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Adobe Acrobat XI User Manual Page 546

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