If you have not changed the transparency of your artwork with the Transparency panel, the fills and strokes in the artwork will appear opaque, because the top color knocks out, or cuts out, the area underneath. You can prevent knockout by using the Overprint options in the Attributes panel. After you’ve set your overprint options, you can preview the overprinting effects on‑screen.
InDesign also has overprint simulation, which is useful for simulating the effects of overprinting spot and process inks on a composite printing device.
Black ink applied to text or native InDesign objects is overprinted by default to prevent misregistration of small black-type characters positioned over color areas, or of color areas outlined with black lines. You can change black ink settings using Appearance Of Blackpreferences.
Your design workflow may require a certain color to be set to overprint. For example, you want to print all the text in your publication in a specific color. Consider the following options:
Create an object style that uses the spot ink as the fill or stroke with a matching overprint fill or stroke.
Create a separate layer for objects that contain your spot color and assign them to black.
Create a composite PDF and change overprint settings within the PDF.
Assign overprint settings in your RIP.
Apply overprint settings to an image or object and add it to your library, or edit a placed file in its original application.
Automatic trapping in InDesign—either as built‑in trapping or Adobe In‑RIP Trapping—nearly eliminates the need for manual overprinting. However, manual overprinting can be an effective solution in the rare cases when you can’t use automatic trapping.
Use the following guidelines to determine whether or not to use overprinting:
Consult with your service provider to see if their output devices support manual overprinting.
Overprint when the artwork doesn’t share common ink colors and you want to create a trap or overlaid ink effects. When overprinting process color mixes or custom colors that don’t share common ink colors, the overprint color is added to the background color. For example, if you print a fill of 100% magenta over a fill of 100% cyan, the overlapping fills appear violet, not magenta.
Don’t overprint when using a stroke to trap two process colors. Instead, you specify a CMYK stroke color that uses the higher value from the corresponding inks in each original color.
Make sure that you and your prepress service provider agree on when and how to overprint manually, because doing so will significantly affect trapping options specified in the Print dialog box. Overprinting is supported by most, but not all, PostScript Level 2 and PostScript 3 devices.
You can overprint strokes or fills, paragraph rules, and rules above footnotes. You can also simulate overprinting of spot colors.
You can overprint strokes or fills of any selected paths using the Attributes panel. An overprinted stroke or fill doesn’t need to be trapped, because overprinting covers any potential gaps between adjacent colors. You can also overprint a stroke to simulate a trap (by overprinting a color you’ve manually calculated as the proper combination of two adjacent colors).
Keep the following guidelines in mind as you apply manual overprinting:
If you use the Overprint Fill option on a 100% black stroke or fill, the black ink may not be opaque enough to prevent the underlying ink colors from showing through. To eliminate the show-through problem, use a four-color (rich) black instead of a 100% black. Consult with your service provider about the exact percentages of color to add to the black.
When using a stroke to trap objects (but not text characters), adjust the stroke alignment so the stroke falls outside the path or object, rather than inside or centered on the path.
When using a stroke to trap two spot colors or a spot and a process color, you usually apply the lighter color to the stroke, and overprint the stroke.
Use the Separations Preview panel to preview how colors will overprint.
Select one or more paths with the Selection tool or the Direct Selection tool , or select text characters with the Type tool. To overprint the stroke of a path that is pasted inside a frame, you must first select the nested (inner) path using the Direct Selection tool.
A. Cyan (bottom layer) B. Magenta (middle layer) C. Yellow (top layer)
The Overprint Stroke and Overprint Gap options in the Paragraph Rules dialog box can be saved as part of a paragraph style.
InDesign can automatically insert a rule to separate footnotes from the body of the document. You can choose to overprint the rule.
Overprint simulation is useful for simulating the effects of overprinting spot inks with different neutral density values (for example, red and blue). When you print to a composite output device using overprint simulation, you can see if the resulting color is one that you want to overprint or knock out.
To knock out black objects in InDesign, you must prevent the black swatch from overprinting. Unlike most color swatches, which knock out by default, the black swatch overprints by default, including all black strokes, fills, and text characters. The 100% process black appears as [Black] in the Swatches panel. Knock out black objects by either deselecting the overprint default in Preferences or by duplicating the default black swatch and applying the duplicated swatch to color objects that knock out. If you disable the overprint setting in the Preferences dialog box, all instances of Black knock out (remove underlying inks).
It can be cheaper and easier to have the print shop overprint process black on the press.
Overprint [Black] Swatch at 100% does not affect tints of [Black], unnamed black colors, or objects that appear black because of their transparency settings or styles. It affects only objects or text colored with the [Black] swatch.