When the job is printed on oversized paper and cropped to the final page size (the page size specified in the layout program), the trimming lops off the overlapping artwork, resulting in a nice bleed in the finished piece.
Occasionally, though, no one tells the artist supplying a page-size image about the bleed thing. Or the artist is too new to the magical world of printing presses to understand the requirements. They were told the publication is 6" by 9" so they give the client a 6" x 9" piece of artwork for the cover. The client/boss gives it to the designer who says, "Uhhh, this is too small. It's supposed to bleed on three sides: top, bottom, and right."
If the designer just positions the artwork on the page so it perfectly fits — no overlap — then there's a good chance the the final printed pieces will show slivers of the paper color at the edges of the page, because of how paper can shift slightly as it moves through the presses at lightning speed. [Edit: Actually, the problem would occur at the trimming stage, not as a result of misregistration. As one of the handful of printers who read the story and e-mailed me about this said, "The real reason for bleed is more mundane: It is because at the trimming stage, the physical action of the guillotine on the piles of printed paper cannot ever guarantee a perfect cut - even on the most expensive guillotines." Thank you! —AM]
Recently, two different clients of mine encountered this exact situation, and someone else wrote about it in one of the prepress forums online. Must be something in the air. Interestingly, in all these cases, the simplest solution — tell the artist to make it bigger — was impossible, because they were dealing with legacy files and the original artist had dropped off the face of the planet.
If you're very lucky, the image will lend itself to scaling without pixellation or ruining its design. Just size it up in the layout program so you've got a bleed, and go on your way.
More often, though, the artwork contains other elements (such as a special type treatment or a fancy border) that would look too big if it was scaled up, or off-balance if only a couple sides needed to bleed. In that case, the solution is to roll up your sleeves and "make it bigger" yourself in an artwork program.
You don't want to scale it up the artwork program either, just increase its dimensions — its own page size — slightly. Then you'll add art elements to the added area. Your handiwork will likely never see the light of day because it's going to end up outside of the live page area, in the bleed allowance. But in case the paper shifts slightly on press and some of this overlapping artwork lands in the "live" area, users won't see blank paper.
Adding Bleed to Vectors
If it's a vector EPS, AI or PDF file, open it up in Adobe Illustrator and pray any fonts it uses were embedded or converted to outlines. (If it requires fonts you don't have, you'll have to rasterize it in Photoshop and correct it there. It's a last resort.) In Illustrator, go to File > Document Setup, and increase the size of the artboard to account for the bleed. In the example of a 6" x 9" page that needs to bleed on three sides, you'd change the artboard width from 6" to 6.125," and the height from 9" to 9.25."
After you click OK you'll see that your artboard grew from the center and the artwork itself stayed in position. That's exactly what you want for the Height, since there's now .125" of extra room above and below the artwork. But since you want the Width's additional .125 to only appear on to the right of the artwork, you'll need to move all the artwork .0625" to the left. (That's .125 divided by 2.) Just choose Select > Select All, then Object > Transform > Move and enter "-.0625" in the Horizontal field, and click OK.
Now you need to fill in the empty artboard area you have on the top, bottom and right sides of the artwork.
Use your Direct Selection tool to extend edges of elements into the bleed area, or fill the empty space with 0-stroke rectangles filled with the same color as adjacent art elements. You don't have to be perfect here. Remember, you're just trying to avoid slivers of paper showing up. Consider that at least 95% of what you create will be lopped off during the trimming process, assuming your commercial printer keeps their presses maintained.
Save your file with a different name so you know it's the one you added the bleed to, place it in the layout program, and voila, it's large enough to overlap the trim edge. Since you're not scaling it, the important elements inside the live area are untouched, they're exactly as the original artist intended.
Adding Bleed to Rasters
Use the same basic procedure when you need to add a bleed allowance to a raster image. Open up the artwork in Photoshop, then "make it bigger" in the Image > Canvas Size dialog box. If you turn on the Relative checkbox, you can enter the actual bleed amounts in the Width and Height fields instead of adding that measure to the existing dimensions. "Relative" means "add this amount to what's already here."
Unlike Illustrator, Photoshop lets you specify how the extra canvas area should be added to the image (instead of just adding it evenly on all sides). You do this by selecting one of the nine boxes in the little Anchor grid in the Canvas Size dialog box. If you want the additional measure added to the top, bottom and right sides of the existing image, click the middle box in the left-most column of the grid. The selected box stands for the existing image; so you're telling Photoshop to "grow" the canvas above, below and to the right of it.
(It's times like these that I wish I could include a screen shot! I'm working on that …) [Edit: This article was reprinted with permission by CreativePro.com on Aug. 6, 2007, and they included screenshots! Check it out, they called the story "I Bleed for You" … heh. —AM]
Click the OK button and you'll see the empty canvas area for your bleed allowance appear above, below and to the right of the existing artwork. I recommend that at this point, you don't just start painting in it willy-nilly. It's too easy to accidentally mess up the original art. Instead, add another layer in the Layers panel and do all your fill-in work on that layer. (Creating a slightly feathered layer mask here can also help keep your additions from impinging too much on the original artwork on the layer below.)
If the artwork's edges are a flat color, you can pick up that color with the Eyedropper and then paint that color into the canvas area on Layer 2, or just fill selection rectangles with it, for that matter. If the edge is some sort of pattern or texture, you can use the Clone Stamp tool to pick up pixels near the edge of the art in Layer 1 and paint them into the empty canvas area in Layer 2. You can even just copy and paste thin rectangular selections from the artwork to the empty canvas area, overlapping them slightly and blurring the edges so the transition from the real artwork to the fill-in you're making in the bleed isn't too harsh.
Again, remember most of what you're adding is going to get lopped off anyway, so don't get too obsessive about it. People will be focusing on the interesting middle parts of the art. You're just trying to eliminate any distracting slivers of paper show-through at the extreme edges.
Finally, save your file under a different name, flatten it into a TIFF if necessary, and place it into your layout program. And there you go, a bleed allowance on the artwork without having to scale it.
Remember all your painstaking attention to detail on this project when your next review rolls around!