Pre-Press Terms and Definitions

ALPHA CHANNEL: A CHANNEL in a computer graphic which does not contain color information. Alpha channels are usually used to store selections (MASKS) or transparency information.

ANTI-ALIASING: A technique for making edges appear smoother and eliminating "jaggies" by filling in the edges of an object with pixels that are between the object's color and the background color. Anti-aliasing creates the illusion of smoother lines and smoother selections. Not appropriate for Web graphics which are transparent, because the intermediate pixels become opaque, making the image look like it has a "fringe" or "halo" around it.

ATTRIBUTE: A font characteristic (such as Bold, Italic, etc.) created by hilighting a font and clicking on a button. Font characteristics created in this way may not print correctly to an IMAGESETTER. Instead of, for example, making a font bold by hilighting it and using the "Bold" attribute, you should choose the bold version of the font from your Font menu.

BANDING: Undesirable "stairstep" color breaks in a smooth gradation or color vignette, caused by gradations that are excessively long, or by limitations in the number of colors available in an electronic file or the number of colors that can be reproduced on press. Can usually be minimized by adding small amounts of noise to the gradation.

BITMAP: A RASTER GRAPHIC image made up of PIXELS that are either completely black or completely white, with no color or shades of gray. Sometimes called a "line shot." The most appropriate image mode for scanned logos or type that are not in color and do not contain shades of gray.

BITMAP FONT: A font used to display text on a computer screen. The letters in a bitmap font are broken up into pixels; if the font is sent to a printer, or enlarged to large point sizes on the screen, the letters will look "jaggy." Contrast OUTLINE FONT.

BLEED: Extra image that extends beyond the edge of the page. Any time an image or a color is printed to the edge of a page, the image or color should extend at least 1/8" off the edge so that when the page is trimmed on a mechanical cutter, small variations in the trim will not result in a white line down the edge of the page.

CD-RECORDER: A device used to produce CD-ROMs on special blank recordable CDs.

CD-ROM: Compact Disc-Read Only Memory. A small optical disc which contains up to 74 minutes of audio information, up to 640 MB of computer data, or any combination of the two.

CHANNEL: One "plane" of a RASTER GRAPHIC, usually containing color information but sometimes containing selection or transparency information as well. An RGB image always has at least three channels: one for Red, one for Green, and one for Blue. Combining these three channels gives the appearance of a full-color image. Similarly, a CMYK image always has at least four channels: one for Cyan, one for Magenta, one for Yellow, and one for Black. Extra channels that do not contain color information are called ALPHA CHANNELS.

CHOKE: A TRAP formed when the background color is lighter than the foreground object, so the background color is pushed under the edge of the foreground object.

CHARGE-COUPLED DEVICE: A type of sensor used in many FLATBED SCANNERS, particularly consumer-quality scanners, and in camcorders. A CCD converts light into electrical impulses. CCDs tend not to be sensitive to low areas of light; for this reason, CCD scanners usually produce scans which lack detail in the shadows.

CLIPPING PATH: A path made with Photoshop's Pen tool, which is used to make part of an image transparent. When a clipping path is created, everything inside the path is opaque, and everything outside the path is transparent. Images with clipping paths should be saved as EPS files. Since clipping paths are POSTSCRIPT objects, they print correctly only on PostScript printers. (Note: On Windows computers, images with clipping paths may appear on-screen in a white background, due to a technical limitation in Microsoft Windows. They will print correctly to a PostScript printer.)

CMYK: A COLOR MODEL used in color printing. The CMYK color model simulates a full range of color by mixing varying percentages of four primary colors: Cyan, Magenta, Yellow, and Black. When these colors are printed on a page, they subtract from white light that reflects off the page, creating the illusion of color; for this reason, CMYK is a "subtractive" color model. Almost all color printing is done by using these four colors; color printing done this way is called "four-color" or PROCESS printing.

COLOR BAR: A series of colored squares printed off the edge of a page. These color squares are used to verify the accuracy of the film used to make printing plates, and are used by a press operator to help calibrate the printing press. Progressive color bars are color bars which run along the entire edge of an imposed flat, and are used to verify correct color on press.

COLOR CORRECTION: The process of adjusting the color in a scanned image so that it more closely matches the original image, or to compensate for flaws (such as overexposure, underexposure, or color casts) in the original image. Color correction is a normal part of the pre-press process; almost all scanned images go through some level of color correction.

COLOR KEY: 3M's trademarked system for producing overlay proofs. A Color Key is an inexpensive form of contract proof that is usually used for jobs where color is not critical. See also MatchPrint, Water Proof.

COLOR MANAGEMENT SYSTEM (CMS): Any system that is used to ensure that an image produced by a scanner looks the same on screen and when printed on a printer, no matter what brand of monitor or printer is used. When all the elements (scanner, monitor, and printer) are properly configured, the color management system should make sure that the image from the scanner looks the same on screen and when printed out, at least within the limitations of the screen and printer.

COLOR MODEL: A system used to reproduce a wide range of colors using some sort of primary color system. Some common color models include RGB, CMYK, Hexachrome, and Lab. Different color models are used for different purposes; for example, the CMYK model is used to reproduce color on a printing press, and the RGB model is used to simulate colors on a computer model or TV screen.

COLOR SYNC: Apple's popular COLOR MANAGEMENT SYSTEM. It is available for Macintoshes and IBM PCs. Color Sync uses device PROFILES to manage color.

COLOR TARGET: An image used as a standard reference when comparing the color produced by a scanner or displayed on a monitor to a PROOF or printout. A good color target should contain swatches of the primary colors (Cyan, Magenta, Yellow, and Black) at different densities; swatches of primary color combinations (Cyan+Magenta, Cyan+Yellow, Magenta+Yellow, etc.); good detail in hilights and shadows; and fleshtones. The file "Ole no Moire" that is included with Photoshop is one example of a color target.

COLOR TEMPERATURE: A measure of how white a light source is. Color temperature is measured in degrees Kelvin, and corresponds to the color of a black-body radiator heated to that temperature. For pre-press purposes, white light is normally considered to be light at 5000 Kelvin. Light with a lower color temperature is more yellow or red; light with a higher color temperature is more blue. Light sources that are not 500 Kelvin should not be used to check color accuracy or examine PROOFS.

COLOROMETER: A special type of densitometer designed to analyze the color on a printed sheet and produce its spectral breakdown, color value, etc.

COMPOSITE: An image or page that is printed in color, rather than being printed as SEPARATIONS. Generally speaking, a page is printed as a composite only for proofreading, or when the page is going to a color printer. When a page is printed to an IMAGESETTER, it is sent as separations.

COMPUTER-TO-PLATE (CTP): A system where printing plates are generated directly from a computer file. In traditional DESKTOP PUBLISHING, a computer file is printed to an IMAGESETTER to produce sets of photographic film, which are used to make printing plates. In CTP, a device called a PLATESETTER is used to create the printing plates directly from the computer. In a CTP workflow, PROOFS must be generated digitally; in traditional workflows, the proofs are made from the film before the film is used to create the plates.

CONTINUOUS TONE: An image made of continuous shades of gray or continuous ranges of color. Images such as photographs are continuous tone; so are scans which are made in color or grayscale. Printing presses cannot reproduce continuous tone, instead, they simulate shades of gray by using a HALFTONE. Devices which can print continuous tone, such as IRIS printers and DYE-SUBLIMATION printers, do not create accurate representations of what a page will look like when printed on a press.

DENSITOMETER: A device used to verify the accuracy of a sheet of film or a printed piece. A densitometer works by shining a light through a sheet of film (in the case of a transmission densitometer) or reflecting light off an object (in the case of a reflection densitometer) and measuring how opaque or dense the object is. Densitometers are used to verify that ink is being laid down properly on a sheet of paper, or that the film used for making printing plates is properly exposed and properly developed.

DESKTOP COLOR SEPARATION (DCS): A standard file format for saving CMYK or SPOT-COLOR graphics. A graphic saved in DCS format will usually create several files on disk: a low-resolution STAMP, and several high-resolution files, each containing one CHANNEL of the original image. The low-resolution stamp can be placed in a PAGE LAYOUT program; when the image is ready for final output, the high-resolution files will be sent to the printer or IMAGESETTER. There are two standards for DCS: DCS 1.0, which can be used only for CMYK images; and DCS 2.0, which can be used for CMYK or spot color images, and which can create a stamp plus several files, or a single, high-resolution file.

DESKTOP PUBLISHING (DTP): Production of printed materials, assembling of pages, and creation or manipulation of images on a desktop computer. This is now the norm in the graphic arts industry for producing advertising materials, publications, etc. Prior to 1984, all such work was done by hand, by cutting apart and combining sheets of film containing images and letters (a process known as "film stripping").

DIGITAL PROOF: A PROOF produced by means of a special printer that is designed to simulate, as closely as possible, the behavior and color of a printing press. A digital proof is produced without using film; hence, sometimes called a "filmless proof."

DMAX: (1) A measure of the darkest shadow that can be scanned by a SCANNER that will still show visible detail. The higher the DMAX of a particular scanner, the wider the range of tones the scanner can capture, and the higher that scanner's DYNAMIC RANGE is.
(2) The density, or darkness, of the exposed part of a piece of photographic film. The higher the film's DMAX, the darker the exposed areas of the film are.
(3) see TOTAL INK.

DOT GAIN: Darkening of an image when it is printed on a printing press, caused when the ink hits the paper and spreads out. Dot gain is greater on uncoated paper than it is on glossy paper, because the ink soaks in to uncoated paper. Scanned images can be lightened in the MIDTONES to compensate for dot gain; when the image darkens on press, it will match the original.

DRUM SCANNER: A type of SCANNER in which the original to be scanned is wrapped around a glass cylinder and spun at high speed, while a light-sensing device called a PHOTOMULTIPLIER TUBE scans across the cylinder. Drum scanners offer much higher resolution, greater tonal reproduction, higher DYNAMIC RANGE, and greater control over the scanned image than FLATBED SCANNERS do, and allow the image to be COLOR CORRECTED as the scan is being made. Most drum scanners also allow scanning of very large originals. However, drum scanners are very expensive (ranging in price from tens of thousands of dollars to a quarter-million dollars or more) and require a high degree of technical expertise to operate.

DUOTONE: An image produced by taking a black-and-white picture and printing it on top of itself in two different colors of ink (usually black and another color). The result is an image with a subtle range of tone.

DVD: A storage format that uses optical disks similar to CD-ROMs to store information. A DVD disc is about the same size as a CD-ROM, although it stores much greater quantities of information: an entire movie, or several hours of audio, or 5 gigabytes or more of computer data. DVD stands for Digital Video Disc.

DYE SUBLIMATION: A printing process used in some computer printers, whereby ink on sheets of ribbon material is heated and fused with the surface of a sheet of special dye-sublimation paper. Like printing presses, dye sublimation printers reproduce color by using varying combinations of cyan, magenta, yellow, and black. Unlike printing presses, dye sublimation printers produce a CONTINUOUS-TONE image. Dye sublimation printers produce high quality but costly printouts.

DYNAMIC RANGE: A measure of the total range of tones in an image, from lightest to darkest. The greater the dynamic range of an image, the more visible detail it has in hilights and shadows. A scan with a wide dynamic range will reveal a wide range of tones and show visible detail in even the darkest shadows.

ENCAPSULATED POSTSCRIPT (EPS): A file format which describes an image or graphic as a series of POSTSCRIPT commands. EPS graphics can contain RASTER or VECTOR elements, or both. This graphics format is usually produced by drawing software such as Adobe Illustrator or by image-editing software such as Adobe Photoshop, and can be placed in PAGE LAYOUT programs such as QuarkXPress. EPS graphics can not be printed accurately on non-PostScript printers.

FILTER: A PLUG-IN for an image-editing program such as Photoshop, which is designed to produce a certain effect. For example, filters may be designed to blur or sharpen an image, or to create special effects such as motion trails or fractal patterns.

FLATBED SCANNER: A type of SCANNER which works when an original is placed face-down on a sheet of glass and an arm equipped with a light and an electronic sensor sweeps under the glass. This is the most popular type of scanner for home use; however, it offers limited resolution and limited DYNAMIC RANGE. Contrast DRUM SCANNER.

FLEXOGRAPHY: A printing technique where printing plates are made from a flexible rubber material and stretched around a drum on the press. Flexography is usually used for very high-speed, specialty applications, such as printing cardboard cartons, where high reproduction quality is not necessary.

FONT: An alphabet of letters in a particular style. Fonts can belong to any of several types (such as sans serif, decorative, blackletter, etc.). The term "font" used to refer only to a particular style of type in a particular size (for example, Garamond 12 point), and "typeface" was used to refer to the entire collection of letters of a particular style in any size' now, however, "font" and "typeface" are used interchangeably.

FONT FAMILY: Acollection of alphabets in a similar style but in different weights or classifications. For example, the Garamond font family might include Garamond, Garamond Bold, Garamond Italic, and Garamond Bold Italic.

FOR POSITION ONLY (FPO): A low-resolution, "rough" scan used only for creating a page and for indicating final placement and size of a high-resolution image. A layout artist may make FPO scans on a FLATBED SCANNER to use to create the page; the SERVICE BUREAU will then create the final high-resolution scans on a DRUM SCANNER and place them in the file in place of the low-resolution FPO scans.

GAMUT: The overall range of colors that can be produced by a particular COLOR MODEL. (Most people believe, for example, that all the visible colors can be produced by mixing red, green, and blue light, but this is not so; there are colors which no combination of red, green, and blue can produce.) A color which is outside of a particular color model's gamut can not be produced by that color model. The color model normally used to produce colors on press, CMYK, has a very restricted gamut, meaning that many colors can not be reproduced in CMYK under any circumstances.

GCR: Gray component reduction. A method of producing a COLOR SEPARATION that represents dark tones and gray values in an image by combining all four of the primary colors Cyan, Magenta, Yellow, and Black. GCR produces images with richer color and higher saturation than UCR, at the cost of greater TOTAL INK. GCR is usually used to produce CMYK images that will be printed on glossy paper.

GRAPHICS INTERCHANGE FORMAT (GIF): An image file format that can contain at most 256 different colors or shades of gray. Since GIF files can not contain more than 256 discrete colors, this file format is not appropriate for photographic images. GIF images can contain one level of transparency, and are often used on the World Wide Web. GIF images are LZW compressed. (The word "GIF" is pronounced "Jiff.")

HALFTONE: A pattern of dots arranged on an imaginary grid to simulate shades of gray or levels of color. Many printers and all printing presses can not reproduce a CONTINUOUS TONE image; instead, the image is simulated by printing dots of various sizes (the darker the tone, the larger the dots). The pattern of dots is called a "halftone screen."
Halftones are specified by how fine the imaginary grid is (and how small the individual dots are). Newspapers are printed with a halftone screen of 85 lines per inch, meaning that the imaginary grid has 85 individual dots per inch; most magazines are printed at 133 lines per inch; most catalogs, 150 lines per inch; high-quality lithographs and artwork can be reproduced at 175, 200, or even 300 lines per inch. Halftones can also be produced with different kinds of dots; the most common halftone screens are made with dots that are shaped like ellipses, but round dots, square dots, line-shaped dots, and other dot patterns can also be used.
Color images are reproduced on a printing press by creating a halftone screen for each color of ink, and printing the halftones directly on top of one another in a pattern called a ROSETTE. See also STOCHASTIC SCREEN.

HEXACHROME: A COLOR MODEL which uses six primary colors (Cyan, Magenta, Yellow, Orange, Green, and Black) to simulate a full range of colors. Hexachrome is sometimes used to print a job on press where very high color fidelity and saturation is required. However, it is significantly more expensive than conventional CMYK printing, as the paper must make two additional passes through the press for the two additional colors of ink. Hexachrome has a much wider GAMUT than traditional CMYK.

HFS: Hierarchical File System. A disk and CD-ROM format used by Macintosh computers. HFS disks can be read by Windows computers only if they have special software (such as Mac-in-DOS) installed.

HISTOGRAM: A graph showing the relative distribution of PIXELS of various densities in an image. The histogram shows the number of pixels with high density on the left and low density on the right. Its purpose is to show the distribution of tone throughout an image. An image with no shadows will have a histogram with a valley on the left; a histogram with no hilights will have a valley on the right. The histogram below shows an image with a good deal of shadows, MIDTONES, and hilights, but less QUARTERTONES.

IMAGESETTER: A type of printer which prints pages on sheets of photographic film, not on paper. Imagesetters are used to produce the film which will be used to make printing plates for printing something on a press. Imagesetters are much higher resolution than conventional computer printers; they typically print at 2400 dpi, 3600 dpi, or higher.

IMPOSITION: The process of rearranging the pages of a document, such as a catalog or book, to put the pages into a sequence suitable for running on a printing press. An imposed file is printed in flats, and the printed sheets of paper are folded and cut when the book is assembled to create a finished piece with the pages in the correct order. A document that is in READER'S SPREADS must be imposed before it can be printed on a press. See also PRINTER'S SPREADS.

INDEXED COLOR: A system where an image is represented by creating a lookup table of colors, then representing each PIXEL as a number in that lookup table. Indexed color images can contain at most 256 discrete colors. GIF images are one example of indexed color images.

INTAGLIO: A type of press or printing technique which uses engraved plates. The image on the plate is engraved into the plate's surface; then, ink is spread across the plate and wiped off, and the plate is pressed into the paper with great force. The result is a "raised" printing on the surface of the paper. Paper money and postage stamps are printed on intaglio presses. Pronounced "in-TAL-ee-oh."

INTERPOLATION: A process where PIXELS in a RASTER GRAPHIC are created by the computer by using a mathematical process to "guess" what they should be, based on the pixels around them. When an image is increased in size in Photoshop, the new pixels are added by interpolation. Interpolation also takes place when an image is rotated, skewed, stretched, or otherwise distorted.
Because the computer has no way to "know" what pixels should be there when it increases an image's size, it fills in the missing pixels by guessing. As a result, an image whose size has been increased by interpolation will look "soft," or out of focus, and may exhibit stairstepping or other undesirable artifacts. In general, it is not a good idea to use interpolation to attempt to increase an image in size. A scanned image which is too small should be re-scanned rather than enlarged.

IRIS: A type of DIGITAL PROOF produced by an Iris printer. Because Iris proofs are CONTINUOUS TONE and do not match the standard colors used on printing presses (that is, they do not conform to SWOP standards), Iris proofs are inappropriate for checking color or for contract proofing.

ISO-9660: A CD-ROM recording format that is commonly used on Microsoft Windows and Unix computers. An ISO-9660 CD can be read on almost any kind of computer; however, it has many limitations (such as 8-character filenames).

JOLIET: A CD-ROM recording format that is commonly used on Microsoft Windows 95, Windows 98, and Windows NT. A Joliet CD can be read on most kinds of computer, and unlike ISO-9660 it allows long filenames. Joliet is based on extensions of ISO-9660.

JPEG: A form of image compression that reduces the size of a graphic file by discarding some image data. JPEG compression can make a file very small, but it is "lossy," meaning that image quality is lost when the image is compressed. JPEG compression is generally suitable only for use on the World Wide Web; it is not generally considered appropriate for print images. LZW compression is preferable for high-quality images that must be reduced in size. (JPEG stands for Joint Photographic Experts Group, the industry body that created it.)

KERNING: The process of adjusting the space between two letters in a piece of text, to make a more pleasing fit. The term "range kerning" is sometimes used to describe the process of adjusting the space between many letters in a piece of text at once.

KODAK APPROVAL: A type of DIGITAL PROOF that matches the results obtained from a traditional film proof very closely. Kodak Approvals produce high-quality proofs without the expense of printing film. An approval proof is made at the same line screen and with the same HALFTONE as finished film, so it can be used to check the quality of the halftone as well.

Lab: A COLOR MODEL developed as a way to describe mathematically every color that can be perceived by the human eye. Formally known as CIE L*a*b, the Lab color model describes color in terms of its luminosity, or brightness (L), and two axes describing color on an axis from green to magenta (a) and from blue to yellow (b). Since Lab can contain every color in the RGB GAMUT, as well as every color in the CMYK gamut, it is a good intermediary between the two.

LAMINATE PROOF: A type of PROOF, made from film, where each color is laminated to a sheet of paper, in the same order the colors will be printed on press. Laminate proofs most closely simulate the look and feel of a printed piece, and can be made on the actual paper stock that will be run on the press. Contrast OVERLAY PROOF, DIGITAL PROOF.

LAYOUT: (1) The process of assembling words, images, and other elements on a page to form a finished piece.
(2) A STAMP produced by OPI software.

LEADING: The space between lines of type in a block of text. Pronounced "ledding." The name comes from the old-fashioned practice of increasing the space between lines of type by adding strips of lead between blocks of metal type. Leading is specified in POINTS, and includes the point size of the text; so for example 10 point text set with 10 point leading would have the lines of type touching each other. By typesetter's convention, the average amount of leading used in a normal block of body copy is 120% of the point size of the type; so for example 10 point type is normally set with 12-point leading.

LINE SCREEN: A measure of the distance between the rows of dots in a printed HALFTONE, usually expressed in lines per inch or lines per centimeter. Also, "line screen frequency." The higher the line screen, the better-quality the reproduction.

LIVE AREA: The area on a page where you can safely place body copy or other important information. In most cases, important information should not extend all the way to the edge of a page, because there is a chance that the information may be cut off if the page is not cut precisely when it is printed. Typically, the live area of a magazine or newspaper page ends 1/4 to 1/8 of an inch from the edge of the page.

LZW: A form of image compression that reduces repeating elements in an image to mathematical expressions. Unlike JPEG compression, LZW compression is "lossless;" that is, compressing an image with LZW does not cause any image degradation. TIFF images can be LZW compressed. (LZW is named for Lempel-Ziv-Welsh, the mathematicians who jointly invented it.)

MASK: A selection, object, or ALPHA CHANNEL used to block out part of an image. A mask can be used to crop an image to a certain size or shape, or to protect part of an image while the image is being modified.

MATCHPRINT: A trademarked name for 3M's standard laminate proof. MatchPrint proofs are the most common form of contract proof in the printing industry, and offer excellent representation of color as it will appear on press; however, MatchPrint proofs can not be produced on the actual paper stock that will be used on press. See also ColorKey, Water Proof.

MIDTONE: The areas of an image which print at close to 50% gray (or 50% color).

MOIRE: A wavy or repeating interference pattern, caused when two different repeating patterns (such as two screens) overlap each other. This interference is usually undesirable. Moires can occur when an object with a regular structure (such as a screen in a screen door) is photographed and scanned; the regular grid of PIXELS that make up the scan can interfere with the regular pattern of the screen door. (This type of moire is called a "content moire.") A moire can also occur when the image is HALFTONED, if the halftone's SCREEN ANGLES are incorrect.

(The moire in this image was produced by creating two perfect, rectangular grids, placing them on top of each other, and rotating the top grid by seven degrees.)

MULTIPLE MASTER: A special type of FONT that can be varied on more than one axis. Most fonts can be changed in size; a multiple master font may allow the user to change its width, its weight, its serifs, or other parameters smoothly and evenly as well.

OPEN PREPRESS INTERFACE (OPI): A system where a high-resolution image is scanned and placed on a SERVER computer, which automatically creates a low-resolution STAMP of that image. This stamp can be placed in a PAGE LAYOUT application easily and quickly. When the page is ready for final output, it is printed through a SPOOLER on the same server computer, and the server computer automatically switches the stamp with the high-resolution image.
For more information on this topic, please see our "UNDERSTANDING OPI" page.

OPERATING SYSTEM (OS): The special set of software that allows a computer to operate and allows a user to copy files, run programs, and perform other tasks. MacOS, Unix, and Microsoft Windows are examples of operating systems.

OPTICAL RESOLUTION: The maximum resolution at which a SCANNER can scan an image without INTERPOLATION.

OUTLINE FONT: A font that consists of mathematical equations that describe what each letter should look like. Outline fonts can be printed at any size and at any resolution without "jaggies" or loss of quality. Contrast BITMAP FONT.

OVERLAY PROOF: A type of PROOF, made from film, where each color is created on a clear sheet of acetate, and then all four colors are taped to a sheet of paper in such a way that the sheets can be flipped up individually. This type of proof allows examination of each individual layer of color separately, and allows easy checking of TRAPS. Contrast LAMINATE PROOF, DIGITAL PROOF. A Color Key is one example of an overlay proof.

PAGE LAYOUT: The process of assembling text, graphics, and other elements into a finished page. Page layout is done in a layout program such as QuarkXPress. The elements that make up the page (such as pictures, text, and logos) are usually created in other programs (like Adobe Photoshop, Adobe Illustrator, or various word-processing programs) and then assembled in the page-layout program. Modern page layout programs can also perform many of the functions of word processors and drawing software. Once the page is assembled in a page layout program, it is ready to be printed.

PANTONE: A popular system used to specify different colors of ink. The Pantone system lists over a thousand different colors, each one of which is a particular type of printing ink; by specifying colors with their Pantone numbers, any element of ambiguity about the exact color wanted is removed. Pantone inks are used most often in SPOT COLOR printing, but Pantone also publishes guides specifying how the colors can be simulated by mixing the primary colors Cyan, Magenta, Yellow, and Black. (Note: Pantone and the Pantone reference system are registered trademarks of Pantone, Inc.)

PERFECT BINDING: A binding technique where the edges of the pages are ground off and glued together, forming a square-edged binding as in a book. Contrast SADDLE STICHING.

PHOTO CD: A type of CD-ROM used for storing images. Images placed on a Photo CD are scanned on a special workstation, then encoded in a proprietary format using a COLOR MODEL called YCC, which is similar to Lab. The images on a Photo CD are compressed using a proprietary, lossy compression technique; when they are taken off the CD, they can be opened in any of several different color models (including RGB and CMYK) and at any of several different RESOLUTIONS.

PHOTOMULTIPLIER TUBE (PMT): A color-sensing device used in high-end DRUM SCANNERS. Like CCDs, photomultiplier tubes convert light into electrical impulses which can be interpreted by a computer. PMTs, however, are much more sensitive than CCDs, and offer much grater resolution and detail-resolving ability.

PIXEL: The smallest unit of a RASTER graphic. Can be thought of as a single "tile," as in a tile mosaic. A large collection of these tiles makes up the image. One pixel can be only one color.

PLATESETTER: A special type of IMAGESETTER which prints directly onto printing plates instead of onto film. The central component of a COMPUTER-TO-PLATE system.

PLATFORM: A particular type of computer hardware and OPERATING SYSTEM. The most popular platforms for computer graphics and page layout applications are Macintosh computers running MacOS, and Intel-based computers running Microsoft Windows.

PLUG-IN: Any special-purpose add-on for a program, designed to extend the program's capabilities or give it new features. Plug-ins of various sorts are available for most popular page layout, drawing, and image editing software; and may add features like special effects, enhanced color or type controls, new printing capabilities, etc.

POINT: A common unit of measure in page layout. Traditionally, there have been 72.27 points in an inch; most computer programs use 72 points to make up an inch. Type sizes and line thicknesses are usually measured in points.

PORTABLE DOCUMENT FORMAT (PDF): A file format created by Adobe Systems to transfer computer documents from one computer to another without type or graphics problems. Pages are laid out using a conventional page layout program, and then converted to PDF files. The resulting PDF files can be printed, viewed on the World Wide Web, and transferred from computer to computer, even across PLATFORMS and regardless of whether the proper fonts are installed on all the computers.

PORTABLE NETWORK GRAPHIC (PNG): A format for graphics that is useful primarily on the World Wide Web. PNG graphics can contain millions of colors and can be transparent, and are compressed without degradation of the image. However, many Web browsers can not display them.

POSTSCRIPT: A special computer language, called a "page description language," that is used to describe what a printed page should look like. Invented by Adobe, PostScript is the standard way that high-end page layout programs and graphics programs communicate with a printer. The language is interpreted by a device called a RIP, and is then sent to the printer to be printed. PostScript is a "device independent" language, meaning that a certain page will be described the same way no matter what printer it is being sent to; it is up to the particular model of printer to figure out how to print it. Printers which use the PostScript system for communicating with computers are usually more flexible and powerful than their non-PostScript counterparts; non-PostScript printers are not generally useful to the graphic arts community.

POSTSCRIPT FONT: A standard format for OUTLINE FONTS which can be used on Unix, NeXT, Windows or Macintosh computers. A PostScript font contains POSTSCRIPT-language instructions that describe the shape of each letter. PostScript fonts are the standard for the pre-press and graphic arts community.

POSTSCRIPT PRINTER DESCRIPTION (PPD): A file which describes a particular type of PostScript printer. This file tells an application what kind of printer it is, what its resolution is, whether it can print color, what paper sizes it can handle, and other features of the printer. Whenever you print a file to a PostScript printer, you must select the proper PPD to ensure that the program you are using communicates with the printer correctly.

PRESS PROOF: A PROOF made by creating plates and running a job on press. Used as a last-minute check before the entire job is printed. Ideally, the press proof should match the contract proof.

PRINTER DRIVER: A piece of software installed on a computer which tells the computer how a certain printer works, how to access the printer, and what capabilities (such as page size and resolution) the printer has.

PRINTER'S SPREADS: Pages of a document arranged in the order in which they will be printed on a press. In the simplest form of printer's spreads, the back cover and front cover together form one spread; the first page and last page form one spread; the second page and second-to-last page form one spread; etc. Then, the pages are stacked on top of one another, stapled in the middle, and folded in half to form the final booklet. (This type of page arrangement is called SADDLE STICHING.) When this is done, the pages will be in the correct order as a reader flips though the booklet. Contrast READER'S SPREADS.

PROCESS COLOR: Color reproduced on a printing press using mixtures of various amounts of Cyan, Magenta, Yellow, and Black inks. Colors which are broken down into their CMYK primaries are called "process" colors; contrast SPOT colors.

PROFILE: A file which describes, mathematically, how colors look on a particular model of printer, monitor, or scanner. Profiles are used by COLOR MANAGEMENT SYSTEMS to adjust the colors in an image as it passes from one kind of device to another, to make sure that the image looks the same on all the devices even though different devices may represent color differently.

PROOF: A representation of what a page or job will look like when it is printed on a printing press. Proofs are designed to simulate, as closely as possible, the exact appearance a job will take when printed on press; many proofs are made using the same film that will be used to make the printing plates. The proof is used by the designer to verify that the page looks the way he intended, and is used by the press operator to adjust ink flow on press to match the designer's intent. A proof sometimes forms a contract between a designer and a printing firm; the proof indicates how the final printed piece produced by the printing firm should look. Such a proof is called a "contract proof."

PROXY: A screen-resolution representation of a high-resolution graphic image, used for displaying and editing on a computer monitor. A proxy-based image editing application (such as Live Picture) works by allowing the user to do photographic retouching on a low-resolution representation of an image (the proxy), and then replaying the retouching steps on the high-resolution file when the user is finished. The advantage of this technique is that the image retouching is very fast, even if the images themselves are very, very large. The disadvantage of this technique is that, since the user is working with a low-resolution approximation of the image, true pixel-level image editing is not possible.

QUADTONE: An image produced by taking a black-and-white picture and printing it on top of itself in four different colors of ink to produce a subtle range of tone. The principle is the same as for a DUOTONE.

QUARTERTONE: The areas of an image which print at about a 25% gray value or a 75% gray value.

RANDOM PROOF: A PROOF made of a scanned image, to verify the color of the scan and to plan any COLOR CORRECTION or retouching that needs to be done to the image. Random proofs are more reliable than on-screen presentations to demonstrate exactly what a scanned image will look like on press. (The name comes from the fact that the images are placed on the page "at random," not in the position they will be in on the final printed piece.

RASTER GRAPHIC: A computer image made up of small squares or "tiles" of color, called PIXELS. A raster graphic can be thought of like a tile mosaic; the image is broken up into tiny chunks. If you make a raster graphic larger, the tiles become bigger; this can result in a "stairstep" or mosaic appearance. All scanned images are examples of raster graphics. Contrast VECTOR GRAPHIC.

RASTER IMAGE PROCESSOR (RIP): A device--either a piece of hardware, or a computer running special software--that is designed to understand and interpret POSTSCRIPT. A RIP takes a description of a page, specified in PostScript, and turns it into a graphic image suitable for printing on a particular type of printer.

READER'S SPREADS: Pages arranged in the order they would be in if a reader were reading the finished piece. In a magazine or book arranged in reader's spreads, page 1 is the first page; pages 2 and 3 form a spread, pages 4 and 5 form a spread, etc. Publications are not usually printed this way on press; instead, they are arranged in PRINTER'S SPREADS, which are then placed together, folded, and cut to form the final printed piece.

REFLECTIVE: An original, such as a photograph, that light bounces off of to create an image. Opposite of TRANSMISSIVE. In general, transmissive originals produce higher-quality scans than reflective originals.

RESOLUTION: A measure of the level of detail in a RASTER GRAPHIC, measured in PIXELS per inch or pixels per centimeter. The greater the number of pixels per inch, the smaller each individual pixel is, and the greater the detail that can be reproduced with accuracy. Increasing the physical size of a raster graphic decreases the resolution; an image with 300 pixels per inch at 6 inches wide will contain 150 pixels per inch if increased to 12 inches wide. Most low-resolution graphics intended for display on a computer monitor or on the World Wide Web are created at 72 pixels per inch. This is not suitable for reproduction in print; for print reproduction, the image should be 300 pixels per inch or higher, depending on the HALFTONE SCREEN used to print it.

RGB: A COLOR MODEL used to represent colors on a computer screen or television monitor. An RGB color represents color by breaking it down into Red, Green, and Blue light; mixing these three primary colors in varying percentages gives the appearance of a full-color image. Most computer graphics programs and most consumer FLATBED SCANNERS produce RGB images. RGB is not suitable for high-end work intended for reproduction on a printing press; for images intended to be reproduced on press, the CMYK model should be used instead.

RICH BLACK: A black color that is made by mixing other colors of ink with black ink. This produces a much darker, deeper black on press than can be achieved by using black ink alone. Typical values for rich blacks are 40% Cyan, 100% Black or 40% Cyan, 30% Magenta, 30% Yellow, 100% Black.

ROSETTE: A circular pattern of overlapping dots, created when several HALFTONE SCREENS printed with different color inks are placed on top of each other. When a PROCESS COLOR image is printed on press, four halftones are made (one for Cyan, one for Magenta, one for Yellow, and one for Black) and the halftones are printed on top of each other to form the final image. When the halftone SCREEN ANGLES are correct, the overlapping halftone dots form rosettes; if the screen angles are incorrect, a MOIRE may be formed instead.

SADDLE STICHING: A form of binding where pages are laid on top of one another, stapled in the center, and folded in half to form a booklet. Commonly used for magazines. Contrast PERFECT BINDING.

SCANNER: A device which takes an original, such as a photograph, and converts it into a series of numbers that can be used to describe the image to a computer. Scanners always produce RASTER images. There are two basic types of scanners: FLATBED SCANNERS, such as consumer scanners; and DRUM SCANNERS, which are larger, more complicated, and much more costly.

SCRATCH DISK: A hard disk used by a program such as Adobe Photoshop to store temporary (or "scratch") files while the program is being used. Image editing programs are often used to edit very large graphics files--files much too big to fit in the computer's memory. A scratch disk is used to store temporary copies of the image while it is being edited. Many programs require a great deal of free space on their scratch disks; image editing programs, for example, may want free space equal to five times the size of the file being worked on.

SCREEN ANGLE: The angle of the imaginary "grid" of dots that make up a HALFTONE pattern. When different halftones are printed on top of one another (such as is done for all color printing), the halftone angles of each color must be different in order to prevent a MOIRE.

SCSI: A standard type of input/output connection used to attach scanners, hard disks, and other devices to a computer. Almost all Macintosh computers use SCSI connections; it is rarely found on any but high-end PC computers, however. SCSI comes in several different "flavors;" fast/wide and ultra-wide SCSI connectors are faster than regular SCSI connections.

SEPARATION: The process of converting an image to CMYK. Each PIXEL in the image is analyzed for color and reduced to the four primary colors Cyan, Magenta, Yellow, and Black. Separation is a complex process that can be done in one of many ways, depending on the type of printing press that will be used to print the final piece and the type of paper it will be printed on. (Analyzing an image and reducing it to other COLOR MODELS, such as Hexachrome, is sometimes called "separation" as well.) A DRUM SCANNER performs color separation as it scans the image.

SEPARATIONS: Individual sheets of paper or film, each containing exactly one of the colors that will be used to reproduce the page on press. When a page is sent to an IMAGESETTER, the page is usually sent as separations. A job which will be printed in CMYK is sent to the imagesetter as four pages: one for Cyan, one for Magenta, one for Yellow, and one for Black. If the job uses SPOT COLORS, one page will be printed for each spot color being used.

SERVER: A large, dedicated computer, connected to a computer network and used to store files and perform specific network-related tasks, such as spooling or acting as an OPI server. Server computers are not used to perform tasks such as page composition or image editing; instead, they act as a central repository of files that can be accessed by other computers on the network. Servers usually have very large quantities of storage space, and often run a high-performance OPERATING SYSTEM such as Unix.

SERVICE BUREAU: A business which specializes in such jobs as scanning high-resolution images, performing retouching and COLOR CORRECTION, printing files to film using an IMAGESETTER, making PROOFS, and other tasks related to producing the materials necessary to print a job on a printing press. Service bureaus are usually intermediaries between an advertising or design firm and a printer. The service bureau invests in the high-cost equipment, such as DRUM SCANNERS and imagesetters, that it is not practical for a design firm to purchase; and the service bureau has a staff of technicians with extensive training in printing requirements, color reproduction, film handling, color correction, retouching, and other specialized tasks. High-end service bureaus such as Dimension, with extensive experience in complex or demanding jobs, are sometimes called "trade shops."

SPOOLER: A type of SERVER which is used to process jobs being sent to a computer printer. A spooler sits between a computer and a printer. When the job is printed from the computer, it goes to the spooler, not to the printer; the spooler then sends it to the printer. This is done if the printer is slow (so the computer will not be tied up while the printer is printing the job), or if the spooler is required to perform some kind of action, such as replacing low-res OPI images with their high-res counterparts, before the job reaches the printer.

SPOT COLOR: Color reproduced on press by using a special ink of the exact color wanted, rather than being reproduced by mixing different percentages of the primary colors Cyan, Magenta, Yellow, and Black. Since each spot color requires a special ink and an additional pass through the printing press, most color on press is reproduced by using PROCESS COLOR instead. Spot color can be combined with process color for additional impact, or where a special color (such as a company logo color) is required. See also PANTONE.

SPREAD: (1) A TRAP created when a light-color object is placed over a dark-color background; the light color object spreads out into the background.
(2) A single set of pages placed together side-by-side for reading or printing. When two or more pages are printed on the same sheet of paper or film, the result is referred to as a "spread."

SPREADS: A set of pages placed side-by-side when printed (PRINTER'S SPREADS), or for reading (READER'S SPREADS). To print spreads is to print two or more pages together on a single sheet of paper or film.

STAMP: A small, low-resolution thumbnail of a high-resolution scan. This small thumbnail image can be transferred from place to place easily, and can be placed in PAGE LAYOUT applications such as QuarkXPress even on computers without a great deal of RAM. When the page is finished and is ready for final output, the stamp will automatically link to the high-resolution graphic. Stamps can be created by saving a graphic as a DCS image, or can be created by OPI software.

STOCHASTIC SCREEN: A special type of HALFTONE SCREEN which offers much greater image detail on press and avoids problems with MOIRE sometimes associated with traditional halftone screens. A stochastic screen does not use a regular pattern of dots; instead, it uses an irregular pattern of very small dots, distributed at different densities to simulate levels of color. Stochastic screens are usually used only for very high quality, high-end printing applications. While they produce an extremely high-resolution image, they are more difficult to produce and print than traditional halftone screens, and usually exhibit greater DOT GAIN on press. Stochastic screens are not suitable for reproduction on high-speed WEB PRESSES.

SWOP: Standard for Web Offset Proofing. A rigorously defined color proofing standard designed to ensure consistency between the color you see on a PROOF and the color you will get on a printing press. Proofs which do not adhere to the SWOP standard should never be used to check or approve color.

TIFF: A RASTER file format, developed by Aldus, well-suited to scanned graphics. TIFF images are ideal for placement in PAGE LAYOUT programs such as QuarkXPress, and take up less disk space than the same image saved as an EPS. Not suitable for VECTOR graphics. TIFF images can be LZW compressed to further reduce their size. TIFF stands for Tagged Image File Format.

TIFF-IT: A file format which can contain both RASTER and VECTOR elements. TIFF-IT, an extension of TIFF, was developed as a way to transfer files that contain an entire page (or an entire job). TIFF-IT files are often used to transfer pages to PLATESETTERS and other high-end output devices; the pages can contain TRAPPING and HALFTONE SCREENING information as well as graphic objects. TIFF-IT stands for Tagged Image File Format for Information Technology.

TOTAL INK: A measure of the total percentages of ink printing in a certain area on a page, or a certain area in a CMYK image. For example, if a particular color is being used on a page and that color is made up of 60% Cyan, 60% Yellow, 15% Magenta, and 10% Black inks, then the total ink on that part of the page is 60+60+15+10, or 145. Different printing techniques and different types of paper have different limits on the maximum total ink that can be printed on the page; if such a limit is exceeded, the ink coverage is too high and the page may smear or skip while it is being printed. The total ink allowable for a CMYK image is sometimes called the DMAX, or maximum density.

TRACKING: The overall letter spacing of a particular piece of text. See also KERNING.

TRANSFER FUNCTION: A mathematical equation embedded in an image file, which is used to modify the image at the moment it is printed. Transfer functions are usually used to lighten images to compensate for DOT GAIN.

TRANSMISSIVE: An original, such as a 35mm slide or transparency, which light passes through to produce an image. Opposite of REFLECTIVE. In general, transmissive originals produce higher-quality scans than reflective originals.

TRAP: To compensate for possible misalignment of colors on a printing press by making objects of different colors overlap slightly (usually by no more than a few hundredths of an inch). When an image is printed on press, each color if ink is printed in a separate pass on the page. If the page moves slightly or the printing plates are not in precise alignment with each other, the result is a slight misalignment of the colors. By causing objects of different color to overlap each other very slightly, this misalignment is not noticeable in the final printed piece.

TRITONE: An image produced by taking a black-and-white picture and printing it on top of itself in three different colors of ink to produce a subtle range of tone. The principle is the same as for a DUOTONE.

TRUETYPE FONT: A standard format for OUTLINE FONTS which can be used on Windows or Macintosh computers. The TrueType format was developed by Apple Computer, Inc. TrueType fonts generally are less reliable than their POSTSCRIPT counterparts.

TYPEFACE: An alphabet of letters in a particular style. Typefaces can belong to any of several types (such as sans serif, decorative, blackletter, etc.). The term "font" used to refer only to a particular style of type in a particular size (for example, Garamond 12 point), and "typeface" was used to refer to the entire collection of letters of a particular style in any size' now, however, "font" and "typeface" are used interchangeably.

UCA: Undercolor addition. A technique used to increase the saturation and vibrancy of an image by adding Cyan, Magenta, and Yellow inks to areas where a lot of Black ink is printing. The result is more vibrancy but higher TOTAL INK.

UCR: Undercolor removal. A method of producing a COLOR SEPARATION that removes Cyan, Magenta, and Yellow inks from dark areas of an image and replaces them with Black. UCR produces images with lower TOTAL INK than GCR, although the images typically are not as saturated or vibrant. UCR is usually used to produce CMYK images that will be printed on uncoated paper, such as newsprint.

UNSHARP MASKING: A technique used to make scanned images sharper. The process of scanning an image can make the image appear soft; high-end DRUM SCANNERS perform unsharp masking automatically to create a sharper, crisper image. FLATBED SCANNERS usually do not perform unsharp masking. Image editing applications such as Adobe Photoshop can be used to unsharp mask an image. (The name "Unsharp Masking" comes from the pre-computer photographic process used to sharpen a blurry negative.)

VECTOR GRAPHIC: A computer graphic made up of a mathematical description of lines, fills, and shapes. Vector graphics can not be used to represent objects such as photographs; instead, they are used to represent objects with smooth lines and hard edges, such as logos or text. Since vector graphics are not made up of PIXELS, they can be resized, stretched, or enlarged indefinitely with absolutely no loss of quality. Vector graphics are created in a drawing program such as Adobe Illustrator. Contrast RASTER GRAPHIC.

WATER PROOF: DuPont's trademarked laminate proof. Water proofs make excellent contract proofs; they offer outstanding color fidelity, and can be produced using the paper on which the job will be printed. See also ColorKey, MatchPrint.

WEB PRESS: A high-speed, high-throughput printing press which prints on a continuous roll of paper. The paper is then cut apart by a slitter to form final sheets. Web presses are usually used for high-volume print runs, because of their great speed; smaller runs are generally printed on presses that print a single sheet of paper at a time.

WHITE POINT: The COLOR TEMPERATURE of a white pixel on a computer monitor. Most computer monitors have a white point of 6500 Kelvin (or higher), which means that white objects on the monitor are actually blue-white, rather than pure white. This in turn means that colors displayed on the monitor are inaccurate.

XTENSION: Any PLUG-IN for the PAGE LAYOUT program QuarkXPress, which extends the program's functionality or gives it new features.