General Printing Terms
Bleed: Where graphical elements (solid colours, images etc.) run right to the edge of the finished paper size. To allow for deviations in cutting the paper to finished size an element that bleeds off the page is typically extended about 3mm beyond the trim lines. The amount of bleed allowance may vary depending on the method of printing and the press used.
CIE LAB: This standard specifies colours by one lightness coordinate and two colour coordinates: green-red and blue-yellow.
Colour Gamut: The range of colours that a device such as a monitor or printer can produce.
Color Key: This is an overlay proof created from the film separations that places each ink color on a separate clear acetate sheet then assembles them together over white paper. Color Key is actually a brandname for a specific process that is often used generically to apply to any overlay proofing system. See Overlay Proofs for a complete description.
Colour Model: An industry-standard for specifying a colour, such as CMYK.
Colour Separation: A set of (usually) four colour negatives - one filtered for each Process Colour. More.
Colour Space: A method of representing colours in terms of measurable values such as the amount of red, yellow and blue in a colour image.
Crop Marks: These show a printer where to trim pages down to their final size.
Flexography: Frequently used for printing on plastic, foil, acetate film, brown paper, and other materials used in packaging, flexography uses flexible printing plates made of rubber or plastic. The inked plates with a slightly raised image are rotated on a cylinder which transfers the image to the substrate. Flexography uses fast-drying inks, is a high-speed print process, can print on many types of absorbent and non-absorbent materials, and can print continuous patterns (such as for giftwrap and wallpaper). Some typical applications for flexography are paper and plastic bags, milk cartons, disposable cups, and candy bar wrappers. Flexography printing may also be used for envelopes, labels, and newspapers.
Folio: Page numbering and associated information - publication, date, website etc.
Four-Colour Printing: The use of the four process colours (i.e. CMYK) in a combination to produce most other colours.
Gutter: The space between columns on a printed space. Also the space allowed between the left-hand side of your page information (text, images etc.) and the publication's binding. The thicker the publication, the more space needs to be left so that the information doesn't "disappear" into the binding.
High-fidelity colour: A form of Process Colour that builds from more than the CMYK plates. Hexachrome is the brand name for such colour.
Intaglio printing: In this method, the area of the image to be printed is recessed into the surface of the printing plate and the recessed areas are filled with ink. The incised image may be etched, engraved with chemicals or tools. The image to be printed is incised into the plates, the incisions filled with ink, and excess ink wiped from the plates. Heavy pressure is applied to transfer the ink from the plates to the paper, leaving the surface slightly raised and the back side slightly indented.
Keyplate: In traditional preparation of color separations, the key plate contains the detail in the art. This is normally the black printing plate. Because the black printing plate was often the key plate, the K in CMYK represents the key plate or black.
LPI: (lines per inch) is an important measurement related to the way printers reproduce photographic images. The LPI is dependent on the output device and the type of paper. Countries using the metric system may use lines per centimeter (L/cm).
To simulate shades of gray using only black ink a printer prints varying sizes and patterns of halftone spots (spots are made up of many dots of ink/toner). Small halftone spots (fewer dots) create the visual illusion of a light gray while larger halftone spots (more dots) appear darker, blacker.
The printer uses a halftone grid divided into cells. The cells contain the halftone spots. How close together the cells in the grid are is measured in lines per inch. This is the LPI or line screen.
Offset Lithography: This process works by first transferring an image photographically to thin metal, paper, or plastic printing plates. Unlike other forms of printing, in offset lithography the image on the printing plate is not recessed or raised. Rollers apply oil-based ink and water to the plates. Since oil and water don't mix, the oil-based ink won't adhere to the non-image areas. Only the inked image portion is then transferred to a rubber blanket (cylinder) that then transfers the image onto the paper as it passes between it and another cylinder beneath the paper. The term offset refers to the fact that the image isn't printed directly to the paper from the plates, but is offset or transferred to another surface that then makes contact with the paper.
OLE: Object Linking & Embedding. The creation of object(s) within one program and importing to another (such as a PowerPoint chart into a Word document).
OPI: Open Prepress Interface. An extension of the PostScript page-description language that lets you design pages with low-resolution placeholder images and replace the images with high-resolution images when creating separations.
Pantone®: A widely used spot-colour model.
Pantone® Hexachrome: A High-fidelity process-colour model with an ink set that includes orange, green and black along with enhanced versions of Cyan, Magenta and Yellow inks.
PDF: Portable Document Format. Developed by Adobe Systems, this format allows document that are created in any program to be converted to PDF format which can then be "read" by the free Adobe Acrobat Reader software, regardless of whether the originating software used to originally create the document is available on the viewers computer. PDF files can be created from most programs by using the Adobe Acrobat software.
Pre-flight: The process of checking DTP files before output by the output provider, in order to check if the files will run successfully on the imagesetter. In pre-flight, the files are not actually output on an imagesetter. Files may be opened and examined and/or run through a checking or imagesetter-emulation program.
PostScript: Once the de facto standard for electronic distribution of final documents meant for publication, PostScript is steadily being supplanted by one of its own descendants, the Portable Document Format or PDF in this area. By 2001 there were fewer printer models which came with support for PostScript, largely due to the growing competition from much cheaper non-PostScript ink jet printers (PostScript interpreters added significantly to printer cost), and new software-based methods to render PostScript images on the computer, making them suitable for any printer (PDF provided one such method). PostScript fonts come in two types - the screen font and the printer font and both need to be supplied to a printing bureau.
Printing Plates: Printing processes such as offset lithography use printing plates to transfer an image to paper or other substrates. The plates may be made of metal, plastic, rubber, paper, and other materials. The image is put on the printing plates using photomechanical, photochemical, or laser engraving processes. The image may be positive or negative.
Typically, printing plates are attached to a cylinder in the press. Ink is applied to the plate's image area and transferred directly to the paper or to an intermediary cylinder and then to the paper. In screen printing, the screen is the equivalent of the printing plate. It can be created manually or photochemically and is usually a porous fabric or stainless steel mesh stretched over a frame.
Examples: The printing plates used depends on the type of press, the printing method, and quantity of the print run. A plate is prepared for each color used, or four plates in the case of 4-colour (CMYK) process printing. In general, metal plates are more expensive but last longer and have greater accuracy. Paper plates are usually more suitable for shorter runs without close or touching colors.
Process Colours: Any of the four primary colours of CMYK.
Registration: The printing of specific extra marks so that different artwork can be aligned. These are known as Registration Marks. Registration is to help align different colours to form a continuous tone image. Different printing devices have different methods of creating colour. Often this requires a pass to create one colour component, and then another pass to create more. Combined these should create the optical illusion of colour. But by splitting the colour creation into many discreet passes the process becomes prone to error. These errors can mean that the optical illusion is broken and that the discreet colours become visible. One method of reducing and quantifying error is Registration.
Relief printing: Where the image to be transferred to paper (or other surface) is raised above the surface of the printing plate. Ink is applied to the raised surface then rolled or stamped onto the substrate. The relief printing process is similar to using an inkpad and stamp. Although the image to be printed is raised on the printing plate, relief printing does not necessarily create relief or raised lettering such as found in embossing and thermography. Flexography and letterpress are forms of relief printing.
RIP (Raster Image Processor): A hardware or combination hardware/software product that converts images described in the form of vector graphics statements into raster graphics images or bitmaps. For example, laser printers use RIPs to convert images that arrive in vector form (for example, text in a specified font) into rasterized and therefore printable form.
RIPs are also used to enlarge images for printing. They use special algorithms (such as error diffusion and schochastic) to provide large blow-ups without loss of clarity.
Screen: An area printed at a particular percentage of a colour (including black). For example, the border of a page may have a 30% Black screen, which appears light grey if printed on white paper.
Spot Colour: A single colour applied to one or more places on a page. You can use more than one spot colour per page. Spot colours can be special inks such as Pantone® or one of the standard Process Colours.
Spreads: These are layouts that span two or more side-by-side pages. Spreads are made up of pages that span a fold in the final document.
Swatch Book: The printer uses a premixed ink based on the Color Model identifier you specify; you look up the numbers for various colours in a table of colours often known as a swatch book.
Stock: The material that is printed upon - paper, card etc. For standard sizes and weights see here.
Trapping: The technique of extending one colour so that it slightly overlaps an adjoining colour. Trapping is done to prevent gaps between two abutting colours. Such gaps are sometimes created by mis-alignment of colour plates. More.
True Type: TrueType is an outline font standard originally developed by Apple Computer in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. The primary strength of TrueType was originally that it offered font developers a high degree of control over precisely how their fonts are displayed, right down to particular pixels, at various font heights. (With widely varying rendering technologies in use today, pixel-level control is no longer certain.)