Bleed or the bleed allowance is used in printing and prepress to describe the area that is still being printed but which is outside the actual print and is cut off at the end.
Bleed is important because paper is a medium that is never exactly 100% identical in the printing press, and these fluctuations increase in every processing step such as folding and stitching. If the data were delivered in the “plain” final format alone, a white margin would often be visible at the edge – sometimes at the top, sometimes at the bottom, sometimes on the right and sometimes on the left – which is caused by the offset of the printed image during printing and further processing.
Most printing companies do well with 3mm bleed, Flyeralarm can also cope with a tolerable one millimetre, sometimes the bleed specifications are also in between or – as for large displays and mega posters – much higher, as fabric or tarpaulin warps even more easily.
If in InDesign or other layout software or in imposition software auxiliary marks are placed on the PDF or the print data, then there are also bleed marks that indicate the inner area to which the bleed is applied and the outer area to where the bleed reaches maximum.
The Trimbox is the final format of a PDF file without bleed. For an A4, the Trimbox of the PDF is therefore 210x297mm, while the Bleedbox would be 216x303mm with 3mm bleed all around.
The BleedBox is one of the five PDF boxes. It describes the part of the PDF, including the content and the bleeding. In printing a bleed of 1 to 3 mm is usually required. A PDF file with an A4 page for printing so usually has a Trimbox of 210×297 mm, the trimmed page format. The BleedBox has with 3mm bleed around the page the size of 216x303mm.