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                                        963
SECTION 10.10                                                      Prepress Support



  include areas close to the edges of the medium that cannot be marked because
  of physical limitations of the output device. Content falling outside this bound-
  ary can safely be discarded without affecting the meaning of the PDF file.
• The crop box defines the region to which the contents of the page are to be
  clipped (cropped) when displayed or printed. Unlike the other boxes, the crop
  box has no defined meaning in terms of physical page geometry or intended
  use; it merely imposes clipping on the page contents. However, in the absence
  of additional information (such as imposition instructions specified in a JDF or
  PJTF job ticket), the crop box determines how the page’s contents are to be po-
  sitioned on the output medium. The default value is the page’s media box.
• The bleed box (PDF 1.3) defines the region to which the contents of the page
  should be clipped when output in a production environment. This may include
  any extra bleed area needed to accommodate the physical limitations of cut-
  ting, folding, and trimming equipment. The actual printed page may include
  printing marks that fall outside the bleed box. The default value is the page’s
  crop box.
• The trim box (PDF 1.3) defines the intended dimensions of the finished page
  after trimming. It may be smaller than the media box to allow for production-
  related content, such as printing instructions, cut marks, or color bars. The
  default value is the page’s crop box.
• The art box (PDF 1.3) defines the extent of the page’s meaningful content
  (including potential white space) as intended by the page’s creator. The default
  value is the page’s crop box.

These boundaries are specified by the MediaBox, CropBox, BleedBox, TrimBox,
and ArtBox entries, respectively, in the page object dictionary (see Table 3.27 on
page 145). All of them are rectangles expressed in default user space units. The
crop, bleed, trim, and art boxes should not ordinarily extend beyond the boun-
daries of the media box. If they do, they are effectively reduced to their intersec-
tion with the media box. Figure 10.3 illustrates the relationships among these
boundaries. (The crop box is not shown in the figure because it has no defined re-
lationship with any of the other boundaries.)

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