In fact, I've seen issues surrounding side effects of this topic pop up on the Illustrator User to User forum, and even more recently on the CTP-Q list over at Print Planet. I've covered parts of this topic in different chapters my Real World Illustrator book, but my intention here is to sew it all together so that we all understand what's going on here.
We'll circle around to the topic of EPS near the end of this post, but before we begin, there are a few concepts that you'll need to know first:
1. Illustrator saves files using a dual path method. This means that every time you save a file from Illustrator, TWO files are really being saved.
- When you save your file as a native .ai file, the file really contains private native data (what Adobe engineers refer to as "PGF" which some jokingly refer to as "Paul George Format" -- one of the lead architects of Illustrator), which only Illustrator can read, and also a PDF 1.4 file, which is what InDesign or any other application reads (this is how InDesign is able to place native .ai files -- it's really reading the PDF 1.4 file embedded inside). The key takeaway here is that when you save your file as a native .ai file (which is what almost everyone tells you to do when using InDesign), you're really saving a PDF 1.4 file. This is assuming that the Create PDF Compatible Files option is checked in the Save dialog (necessary if you want to place your file into another app).
- When you save your file as an EPS, the file really contains a PGF file (which only AI can read when the file is reopened) and also an EPS file, which InDesign or Quark sees when you place the file into that application.
- When you save your file as a PDF, the file again (by default), contains PGF (that's what Preserve Illustrator Editing Capabilities does), and also the PDF file in the format that you specify in the dialog (PDF 1.3 thru PDF 1.6).
2. In PDFL (literally, the PDF Language), there are several different ways that a file is cropped, and these are called "boxes" In fact, there are 5 different box settings in PDFL, and a file can contain all of these.
- ArtBox - Also called the bounding box, this area is defined by the art that appears in the document.
- TrimBox - This area is defined by the Illustrator artboard and is the size you specify when creating a new document.
- CropBox - This area is defined by using the Object > Crop Area > Make command in Illustrator.
- BleedBox - This area is defined by the Bleed setting you define in the Save As PDF dialog and extends beyond the TrimBox area.
- MediaBox - This area is defined by the size of the page on which you choose to print your file (is usually determined by the printer, not Illustrator).
These boxes can actually be made visible to the human eye in Acrobat simply by going into the Page Display panel in Acrobat Preferences and checking the Display art, trim, bleed boxes option.
OK, let's apply this knowledge...
Before Illustrator CS2, when creating the "compatible" PDF 1.4 section of the file, AI used the ArtBox as the boundary of the file. Technically, in the land of PDF, this was incorrect. So in Illustrator CS2, Illustrator now "correctly" uses the TrimBox setting when creating the PDF 1.4 file.
This has two immediate consequences on how native Illustrator files are now placed into apps like InDesign. First, if you create a one-inch square logo in the center of your letter-sized page, when placed into InDesign, the entire letter-size page gets placed, not just the 1" logo. Second, if your artwork extends past the TrimBox area in Illustrator (i.e., falls off the page), it will effectively get clipped from the file when you place it into InDesign.
You can "fix" this issue easily enough in InDesign though. When placing the image, choose "Show Import Options in the Place dialog, or just hold the Shift key while you click the Place button when choosing a native .ai file. Since InDesign sees the file as a PDF 1.4 file, you'll get a dialog asking how you want to place the file .You can then choose to place the file using the ArtBox setting instead.
But here's the interesting thing: for some reason, in InDesign, you have to choose one of the box settings, and only one. And if you choose one, you can't use another setting later. Here's what I mean. Let's say you have a large map, and you only want to place a portion of that map in your layout in InDesign. So you open the map in Illustrator, and you draw a rectangle around just the area that you want in your layout. Then you choose Object > Crop Area > Make. Then you save the file as a native .ai and place it into InDesign. You choose to use the CropBox setting and the files imports perfectly, showing just the area within the crop marks. Then, the art director decides to have the map bleed off the side of the page. No problem says you, because the AI file has extra image in it, so you simply extend the picture frame, only to see that InDesign really cropped the artwork at the boundary of the CropBox. There is no extra image space.
In contrast, things were different with EPS. If you were doing the exact same thing with EPS, when you place the file, it comes in using the Crop area. But if you extend the picture frame, the rest of the image is there. This actually made it easy to place files in exact position in your layout, and then simply open the frame to display the bleed.
In reality, you could specify a BleedBox setting. In Illustrator however, the only way to set the BleedBox is to specify a Bleed setting in the Save As PDF dialog box -- which you get only when saving your file as a PDF -- NOT as a native .ai file. In fact, when you save a native .ai file, you have no control over the settings that are used in creating that compatible PDF 1.4 file. So your options are going to be to either create your TrimBox at the size your BleedBox really needs to be when saving as a native .ai file, saving your file as a PDF file and specifying the BleedBox setting, or using EPS.
Now, I know I started this post stating that EPS is dead to me, but this ability to place objects precisely, yet still have the ability to expand a picture frame to see bleed image area is useful. So in non-transparency workflows, I might still find a use for EPS. At least for now.
My ultimate goal is that the Illustrator team realizes this shortcoming and adds true BleedBox support to the next rev of the application. Much like what InDesign does -- where in the Document Setup dialog, you specify a page size (trimbox) and a bleed setting (bleedbox). This would easily solve the problem, and allow me to finally heave EPS into the sea of Syquest drives.