InDesign for QuarkXPress Users [Electronic resources] نسخه متنی

Trapping Controls

InDesign also lets you assign particular trapping to specific pages in your document by allowing you create trapping styles in the Trap Styles palette. For instance, you might want to apply a "no trap" style to a particular spread so that nothing on that page traps. To open the palette, choose Trap Styles from the Window menu (see Figure 97-1).

To create a trap style, choose New Style from the palette menu to open the New Trap Style dialog box (see Figure 97-2). You can also import trap styles from other documents by choosing Load Trap Styles from the palette menu. If you're modifying a trap style, select its name in the palette and choose Style Options from the palette menu.

Creating Trap Styles

Trap style settings should only be created or modified by someone who is familiar with press conditions for the job. Here we can only offer a quick overview of the trap style controls. Service providers can find out more information from

Real World InDesign 2 or the resources listed in Chapter 95.

After giving a name to the trap style, you can specify a default Trap Width for the amount of overlap for inks; there is a separate control for trapping black. You can create traps up to 8 points thick with in-RIP trapping; built-in traps are limited to 4 points (which is already a pretty huge trap). For Trap Appearance, you can specify a join style and an end style.

For images, you can specify how placed bitmap images are trapped: There is an option to specify where the trap falls when vector objects (including InDesign objects) trap to bitmap images. There are options for trapping objects to images, images to images, trapping colors within an image, and trapping 1-bit images.

The Trap Threshold section of the dialog box specifies the conditions when trapping occurs: Step controls the degree colors vary before trapping takes place. Black Color indicates the minimum amount of black before black width trapping occurs. Black Density controls the neutral density value which InDesign uses to recognize black ink (neutral density is described below). Sliding Trap tells InDesign the percentage difference between neutral densities of adjoining colors when a more elegant sliding trap is created. Trap Color Reduction reduces trap color to prevent unsightly dark traps when trapping pastel colors.

Assigning Trap Styles

While you probably only need one trap style for a document, you may choose to apply different styles to different ranges of pages. To assign trap styles to pages, choose Assign Trap Style from the Trap Styles palette menu. In the Assign Trap Styles dialog box (see Figure 97-3), select a trap style you want to assign. Either click All or enter the range of pages (continuous or non-continuous) to which you want to apply that trap style, then click Assign. If you have pages where no trapping is necessary, select [No Trap Style], type the page range, and click Assign. Making this choice disables trapping, and these pages will print faster.

Note that trapping doesn't occur when you assign trap styles, only when you actually print color separations from the document. There is no preview of trapping as there is in some high-end trapping software. The resulting traps only appear on the separation plates.

Ink Controls

We discuss the ink aliasing capabilities of the Ink Manager in Chapter 95, but InDesign hid some trapping controls there, too. Remember that the Ink Manager lives in the Advanced panels of the Print, Export EPS, and Export PDF dialog boxes and in the Swatches palette menu. Since InDesign's trapping happens at the ink level, there are three controls in the Ink Manager that influence trapping. First, each ink can be assigned a Type: Normal for process and most spot color inks, Transparent for clear inks like varnishes, Opaque for heavy, non-transparent inks like metallics, and OpaqueIgnore for heavy, non-transparent inks to prevent trapping along an ink's edges.

Each ink can also be assigned a neutral density (basically, how dark the ink is if you were to see it in grayscale). This value, which may be adjusted to match industry standards in different parts of the world, is used by the trapping engine to calculate trapping requirements. Finally, Sequence indicates the trapping order of inks, which is a press-specific control.