Before you begin
We are rolling out a new, more intuitive product experience. If the screen shown here doesn’t match your product interface, switch to the help for your current experience.
Before you begin
We are rolling out a new, more intuitive product experience. If the screen shown here doesn’t match your product interface, switch to the help for your current experience.
In offset printing, when using multiple inks on the same page, precise alignment is crucial to avoid gaps where the inks meet. However, it's challenging to achieve perfect alignment on every sheet, leading to misregistration and unintended gaps between inks.
To compensate for misregistration, you can employ trapping, which involves slightly expanding one object to overlap with a different colored object. By default, one ink knocks out any inks underneath to avoid color mixing. Trapping requires inks to overprint, allowing for at least a partial overlap and better alignment.
Trapping typically involves spreading—a light object is expanded into a dark one. This approach ensures that the visible edge of the object or text is defined by the darker color. By slightly extending the lighter color into the darker color, the visual edge remains intact.
Acrobat offers automatic trapping for color documents using the Adobe In-RIP Trapping engine, available on Adobe PostScript output devices that support it.
The In-RIP Trapping engine precisely calculates and applies adjustments to type and graphics edges throughout your document. It can effectively trap different parts of an object even if it overlaps several background colors. Trapping adjustments happen automatically, and you can create trap presets for specific page ranges. Trapping effects are visible only on color separations generated by the trapping engine, not on the screen within the program.
The trapping engine detects contrasting color edges and applies traps based on neutral densities (lightness or darkness) of adjacent colors, often by expanding lighter colors into darker ones. You can modify the trapping engine's results through the Trap Presets palette settings.
To use Adobe In-RIP Trapping, you need:
Trapping is a complex process influenced by various color, ink, and printing factors. The correct settings depend on your specific press conditions. Unless you've consulted with your print service provider, it's best not to change the default trap settings.
If needed, follow these steps to create a trap preset with custom settings for your document and printing press conditions:
From the All tools menu, select Use print production > Trap presets.
Create the trap preset and assign it to a page range.
Next, select to open the Print dialog box and follow these steps:
From the Output section, select Ink Manager.
If recommended by your service provider, you can adjust the following options for specific inks:
Continue specifying other print options, and then select OK to print your document.
Note: Precise trapping settings ensure better printing results, so always verify with your print service provider before making changes.
A trap preset is a collection of trap settings you can apply to pages in a PDF. Use the Trap presets dialog box for entering trap settings and saving a collection of settings as a trap preset. If you don’t apply a trap preset to a trapping page range, that page range will use the [Default] trap preset, a collection of typical trap settings that are applied to all pages of a new document.
In Acrobat, trap presets and their assignments apply to the document only while it is open; trap settings are not saved in the PDF. This behavior is different from InDesign, where trap presets and their assignments are saved with the InDesign document.
From the All tools menu, select Use print production > Trap presets.
Select an existing preset and then select Create.
In the New Trap Preset dialog, specify the following details and then select Ok:
To delete a trap preset, select the preset from the Trap presets dialog box and then select Delete.
Note: You cannot delete either of the two built-in presets: [No Trap Preset] and [Default].
You can assign a trap preset to a document or to a range of pages in a document. Pages with no abutting colors print faster if you disable trapping on those pages. Trapping doesn’t actually occur until you print the document.
In the Trap presets dialog box, select Assign.
in the Assign Trap Presets dialot, select the trap preset you want to apply.
Select Assign.
If you click OK without clicking Assign, the dialog box closes without changing the trap assignments. Trap assignments previously made using the Assign button are preserved.
Once you are done assigning trap presets, select Ok.
In the Trap presets dialog box, select Assign.
Select the pages you want to disable trapping on and then from the Trap Preset menu, select [No Trap Preset].
Select Assign and then select Ok.
You can change trap preset options whenever you create or edit a trap preset. The same trap preset options are available in Acrobat and InDesign.
In Acrobat, you can view trap presets by going to the All tools menu > Use print production > Trap Presets.
In InDesign, select Window > Output > Trap Presets.
Trap width refers to the overlap amount for each trap, and it varies based on paper characteristics, screen rulings, and printing press conditions. Your commercial printer can help determine the appropriate trap widths for your job.
Here are the default settings:
In InDesign, the value you set for Black Color determines the trap width for solid black or rich black. Rich black is a combination of process black (K) ink with color inks to achieve increased opacity and richer color.
Consult your commercial printer to ensure you use the correct trap widths for optimal printing results.
(InDesign) If you choose Application Built‑In trapping, and you specify a Default trap width or Black trap width larger than 4 points, the resulting trap width is limited to 4 points. However, the value you specified will continue to be displayed, because if you switch to Adobe In‑RIP Trapping, traps larger than 4 points are applied as you specified.
In trapping, a join refers to the common endpoint where two trap edges meet. You have control over the shape of this outside join for two trap segments and the intersection of three traps.
You can experiment with these settings to achieve the desired trapping results. For further clarity or assistance, consult your print service provider.
Step
Creating a trap preset helps control traps within images and between bitmap images (e.g., photos and raster PDFs) and vector objects (e.g., drawings and vector PDFs). Each trapping engine treats imported graphics differently, so it's essential to understand these distinctions when setting trapping options.
Trap Placement
Trap Objects To Images
Trap Images To Images
Trap Images Internally
Trap 1-Bit Images
When creating or editing presets, the "Black Color" value determines what's considered solid black and rich black. Rich black is any black color using additional percentages of process inks to strengthen it—a support screen.
This setting is handy when compensating for extreme dot gain (common with low-grade paper). In such cases, black percentages lower than 100% may print as solid areas. To address this, you can use tints of solid black (screening back blacks or rich blacks) and decrease the "Black Color" setting from its default of 100%. This adjustment compensates for dot gain and ensures the trapping engine applies the right trap width and placement to black objects.
When a color reaches the "Black Color" value, the "Black trap width" applies to all abutting colors, while rich black areas use the "Black trap width" as keepaway traps.
If support screens extend to the edge of a black area, any misregistration can create unwanted halos or distort edges. To avoid this, the trapping engine uses keepaways (holdbacks) for rich blacks. Keepaways keep support screens a specified distance from edges of reversed-out or light foreground elements, preserving sharpness. You control this distance by setting the "Black trap width" value.
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.
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.
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.
When adjusting ND (Neutral Density) values, follow these guidelines:
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.
When working with certain inks, there are special trapping considerations. For instance, when using varnish, you want to avoid affecting trapping. On the other hand, if you have a completely opaque ink overprinting specific areas, traps for items underneath may not be necessary. To handle these situations, ink options are available. Generally, it's best to stick to the default settings unless your prepress service provider suggests changes.
Here's what to do:
The speciality inks and varnishes used in the document may have been created by mixing two spot inks or by mixing a spot ink with one or more process inks.
The trapping sequence, also known as the trapping order, reflects the order in which inks are printed at the press but not how separations are produced at the output device.
For printing with multiple opaque colors like metallic inks, the trapping sequence is crucial. Opaque inks with lower sequence numbers spread under those with higher sequence numbers. This prevents the last applied ink from spreading while still creating effective traps.
To adjust the trapping sequence:
Don’t alter the default trapping sequence without first consulting with your prepress service provider.