What are Bleeds, and Why Do I Need Them?
Extend Your Background Outside The Trim Area. Bleed is the industry term for any image or color that goes right to the edge of the paper. On a press, the artwork is printed on a large sheet of paper, stacked, and then that stack of paper is trimmed down to size. If you do not allow for at least an 1/8 of an inch bleed, any misalignment while cutting will result with the artwork not running to the edge of the paper and creating a white edge. It's just not possible for the cutting machine to cut exactly along the edge through the whole stack of paper. Bleeds give a little room to play with and will ensure the background is all the way to the edge. The background extends 1/8" (.125") beyond the edge of the page and that excess image or color is then cut off as a part of the bindery or finishing process.
The way to create bleed is to simply make certain that the image or color extends off the edge of the page to a distance of 1/8" (.125") wherever you want something to bleed. If you are creating your file in Photoshop, Illustrator, InDesign, or your application of choice, then you must make your document .25" larger overall than your final trim size in both height and width. For example: if the final size is 8.5" x 11" then make your document 8.75" x 11.25".
What are Safe Areas, and Why Do I Need Them?
Keep Content Within "Safe" Area. Just as important as creating your outside bleed, it's important to keep your content within the "safe" area. Text or images that are not meant to be trimmed off the edge of your final printed piece must be 1/8"-1/4" (.125"-.25") from the edge of your layout (the "safe" area). Items placed 1/8" (.125") or closer to the edge are in danger of being trimmed off or showing inconsistent margins.
When creating your document, add guide lines inside the content area that are (at least) 1/8" from the edge and keep all content that you do not want trimmed inside those guide lines.
Bleed and Safe Area Examples
In the examples below, the bleed area extends 1/8" (.125") beyond the trim edge of the page, and the safe area is 1/8" (.125") away from the edge. The "margin" is part of the content but is outside the safe area and in danger of being trimmed. Do not put any content within the margin area that you do not want trimmed; characters, text, speech bubbles, etc.