Special marks are added to your PDF files and to the edge of your parent sheets to assist the offset printing press in proper alignment, trimming and color values. These marks are trimmed off once printing is complete.
Center marks are placed on the horizontal and vertical center of each page to ensure proper printing and trimming. These marks are read by the printing press.
The trim line is the horizontal and vertical mark where your printed sheet (i.e.book page or card) will be cut to size. You should extend your artwork 0.125 inches past this line to account for tiny variances inherent in trimming. You should keep all important content at least 0.125 inches inside the trim line, which is called the safe area.
A project with printing that extends to the edge of the page always needs bleed. Your artwork should extend to the bleed line
, which is positioned 0.125 inches further out than the trim line. Any content found in between the trim and bleed line will not appear in most copies of your final project but this space serves as a buffer and will help you avoid any accidental white borders.
Color bars, or color control strips, are printed in the trim area of a parent sheet. Press operators use the color bars to check for ink density, overprinting, grey balance and more. Color bars are so efficient that they can reveal issues with ink hue, rubber blanket, and impression cylinder miscues.
Registration is the process of precisely lining up cyan, magenta, yellow, and black printing plates so that their overlap produces the full color spectrum. Registration marks (crosshairs) are added to your PDF files and your plates. As printing takes place, the pressman makes sure that both sets of registration marks line up, adjusting their alignment as needed. Once all four colors are printed, the crosshair should be a solid black circle otherwise the press operator will know the job isn’t being printed correctly and will make more adjustments. Without registration, your images can appear blurred, as the four colors may not line up and will exhibit the ‘ghosting’ that you often see in newspaper color photos (since the large web presses used to print newspapers frequently have registration issues).