"Full-bleed" or simply "bleed" printing means printing without a margin; that is, the image prints right up to the edge of the paper. The term originated in the offset printing industry, and for many years it was something you just couldn't do on a computer printer. However, with the advent of photo printers and other high-end color printers, marginless printing is now an option.
How Full-Bleed Printing is Achieved
In traditional offset printing, pages are printed on oversized sheets and then trimmed down to size. If you wanted an image or a color to run right up to the edge, you had to make sure that the artwork for it extended over the edges of the actual margins of the page. In other words, the image had to "bleed" off the page margin. A "full-bleed" page was one in which the images extended over all four page margins.
Applications of Full-Bleed Printing
Because bleed printing could only be done by a professional printer who could handle post-print trimming, it has become associated with high-quality printing. Magazines are almost always printed full-bleed; so are professional quality posters and artwork reprints. Nearly any kind of commercial printing -- such as flyers and spec sheets -- will include bleeding images to achieve a professional look.
Margin Limitations of Older Printers
The first laser and inkjet printers moved paper through their imaging systems by gripping the top and side edges with sets of rubber rollers. Obviously, you couldn't lay ink or toner on the part of the paper the rollers were gripping, so these printers always had minimum margin requirements. While later printers reduced this "gripper" area considerably, they still could not print right up to the edge, so bleed printing wasn't possible.
Full-Bleed Printing on Newer Printers
Many newer inkjet printers have "Borderless" printing technology. The portion of print path which runs under the print head has no grippers, so the print head can actually run over the edge of the paper, thus achieving bleed printing. When you select borderless printing, the print dialog box asks you to specify how much you want to expand your document size to insure that the printing goes over the edge. If you set this expansion too small, you may still wind up with a hairline white border; if you set it too large, you may crop off important parts of your document.
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