InDesign’s Trapping in a Composite PDF
The question of trapping pops up periodically, and as we say in podcast 48: Let the printer do it! Trapping is the correction that is often necessary to cover up for slight misregistration on press. Humans should not have to do manual trapping with overprinting strokes any longer. (If you don’t know what I’m talking about, just smile and be happy that you never had to manually trap a file.)
But every now and again, we hear someone say, “Yes, but we really need to do trapping in InDesign.” Well, InDesign’s Attributes palette lets you control overprinting, and its Strokes palette lets you control stroke thickness and position. Or, even better, you can use InDesign’s built-in trapping feature by printing separations to disk.
But what if you want to create a composite-color PDF file with trapping… that is, you want to be able to open the PDF in Acrobat and actually see the color and print separations there (instead of just seeing black and white pre-separated plates)? For example, let’s say we want to trap this page:
trap3
Here’s what you do:
- Instead of using File > Export, choose File > Print, and then choose PDF from the Printer popup menu. (You’ll need Acrobat Professional installed to see this, I believe.)
- Set up the various panes in the Print dialog box. For example, if you want crop marks, you’ll need to add them in the Marks and Bleed pane.
- In the Output pane, choose In-RIP Separations from the Color popup menu. In this case, the “RIP” is Acrobat Distiller.
- Now you can chose Application Built-In from the Trapping pop-up menu. That tells InDesign to handle the trapping when it writes PostScript to disk (before it gets to the Distiller).
trap1
Note that you can control the Acrobat Distiller settings by clicking the Printer button (on the Mac OS) or Setup button (in Windows) at the bottom of the Print dialog box. Then, when you’re ready, click Print. InDesign writes trapped PostScript to disk and then launches the Distiller to convert it to PDF.
When you open the file in Acrobat, be sure that Overprint Preview is turned on for best effect. Here’s the trapped file in Acrobat (zoomed in a lot, of course):
trap2
(Anne-Marie also wrote this technique up a couple of years ago for DesignGeek.)
And Adobe’s Nick Hodge also wrote about it on his excellent site some time ago. This is a pretty cool hack, leverging “features” (or are they “quirks”) of both InDesign and Distiller…
When I started to show that feature when ID CS1 came out, I saw attendee’s faces expressing Wow !
For those who are fluent in French, A 25 minute QuickTime video tutorial on this subject is available on my site for 7 euros.
http://www.milic.com/indesign/formations/didacticiels-video/index.html
David, you should mention how great it is to have a black (C:30 - K:100) square with a [Paper] knockout shape and how the trapping engine will perfectly trap the cyan all around the square and the shape that is knocking out.
Thanks, Peter. I had forgotten that Nick wrote about this in the good old days. Of course, these days Nick talks more about Excel than InDesign. Sad.
Also make sure that you tell Acrobat to set the trapping key to TRUE. This can either be set with a job setting in Distiller such as PDF/X or manually via the Document Properties in Acrobat.
Otherwise you might get a double-trap occur with trapping libraries at the print provider’s renderer …
Jon
It’s a very cool option and I use it every time I need a trapped composite PDF but I have a little question about it. It doesn’t work with imported eps files but seems to work with native AI files (with PDF compatibility, of course). Can you confirm this?
Thierry, you are correct that this doesn’t appear to work with imported EPS files (at least in CS3). The same image saved as PDF and EPS works with the former and doesn’t with the latter. Wow. That may be a bug.
David and Thierry, you can’t trapp EPS files freely, this is speciffic to the file format and is not an InDesign bug. EPS means ‘Encapsulated PostScript’, so, as it is encapsulated, InDesign is not allowed to change anything in it by definition. The EPS files can carry in not only images, but also speciffic instructions, screen dot shapes, or, for example, different color plate screen angles, and therefore, this is feature, not bug. This is documented in ID help.
Does anyone know how to PRINT the separations from a printers so I can look at them? I’m talking C on one page, M on one page, etc etc.
When I try to print separations from the dialogue box, the printer spits out one sheet with the colours listed on the bottom.
Benjamin, you should be able to choose Separations from the Color pop-up menu in the Output pane of the Print dialog box.
I did that, but when I print, it only prints out one page (but with 4 colours bars and CMYK listed along the bottom).
Any ideas? Or did I stump ya?
Benjamin, I’m sorry but I have no idea what you may be doing wrong. When you print separations, you should get one color per page (cyan on one page, yellow on another, etc.). That’s the whole point of separations. Are you printing seps from InDesign or from Acrobat?