To turn an idea into a printed page requires that one sail on a voyage of artistry, technology and craftsmanship. This glossary highlights some of the more complicated and confusing terms used in that journey.
AM screening: Amplitude modulated screening. The process of turning a continuous tone image (photograph) into a mesh of different-sized dots for printing. AM screening varies the size (amplitude) of the dots in a given area. Also known as conventional halftoning (see halftone).
Bleed: To print to the edge of a page by printing images or colored areas outside the trim area of the page and then cutting the page to size. The area outside of the trim edge is sometimes called the bleed.
Creep: The fact that the outside edges of paper do not line up when you place folded pages inside of one another for binding (see saddle-stitch). Also the name for the amount of horizontal adjustment put on pages to compensate for this bindery phenomenon.
DPI: Dots per inch. A measurement of resolution. An image cannot be measured in DPI until it is printed. Also a measurement of the quality of a printing device or monitor, where generally higher DPI is better.
Dot gain: The tendency of halftone dots to gain in size, which tends to darken an image and degrade its contrast. Printing presses are measured for dot gain. We apply compensation for dot gain and loss when we create plates for printing your piece.
Dot loss: The tendency of small halftone dots to diminish or disappear when printed.
Duotone: An image composed of two screen inks placed on top of each other.
FM screening: Frequency modulated screening. The process of turning a continuous tone image (photograph) into a mesh of same-sized dots for printing. FM screening works by varying the amount (frequency) of dots in a given area.
Gripper edge: The edge of the sheet of paper that goes into the press first. This edge is held by mechanical “gripper” hands.
Halftone: The process of turning a photograph into a mesh of different-sized dots by photographing it with a halftone screen on it. This process is now usually done by software on a scanned image. Printing presses cannot print dots of ink with variable transparency, which is why all images must be screened before printing.
Imposition: The act of arranging pages on a sheet so that many pages can be printed at once. Imposition must take into account the sequence of pages and the margins needed to adjust for bleeds, creep and folding.
Moiré: An unintended pattern caused by applying two different colored halftone screens at the wrong angle.
Offset lithography: The precise term for the most popular process of printing ink on paper. “Offset” describes the blanket cylinder that exists between the printing cylinder and the inked plate. “Lithography” describes the fact that water is used to keep ink only on the imaged parts of the printing plate. This process works because water is attracted to the non-image area while the ink is repelled by the water and attracted to the imaged area.
Perfect binding: A form of book binding where each page is stacked individually and the binding edge is glued to an outside cover. This process does not cause creep because the pages are not folded inside of each other.
Resolution: Sometimes called output resolution. The ratio of dots to length when printed. For instance, monitors “print” images to the screen at 72 dpi, while laser printers typically print at 600 dpi, and imagesetters and platesetters print at least 2400 dpi.
Saddle stitch: A form of binding where each set of four pages is folded and placed inside the next set of four pages, and then the document is bound by stapling or sewing along the fold. This form of binding causes creep and is limited in size by the amount of paper that can be folded and stapled.
Work and tumble and work and turn: Two common imposition techniques used to save prepress and printing time by putting the front and back of a page on the same printing plate. Each plate contains half fronts and half backs. In a work and tumble, after printing on one side of a sheet, the pages are flipped so that the back edge is now the gripper edge. In a work and turn, after printing the first side, the pages are flipped sideways so that the paper is held by the same gripper edge as it was the first time through.