A B C D E F G H I J K L M N O P Q R S T U V W X Y Z     Additive Primaries Red, green, and blue light, which produce white light when combined.   Alpha Channel An 8-bit channel reserved by some image-processing applications for masking or additional colour information.   Anti-aliasing The rendering of hard edged objects so they blend smoothly into the background. A technique for merging object-oriented art into bitmaps.   Artifact A visible indication (defect) in an image caused by limitations in the production process (hardware or software).   ASCII (American Standard Code for Information Interchange) A standard format for representing digital information in 8-bit chunks.     Banding A visible stair-stepping of shades in a gradient.   Bezier Curves In object-oriented programs, a curve whose shape is defined by anchor points set along its arc.   Bit (Binary Digit) The smallest unit of information in a computer. It can define itself one of two conditions (on or off).   Bitmapped An image formed by a rectangular grid of pixels. The computer assigns a value to each pixel, from one bit of information (black or white), to as much as 24 bits per pixel for full colour images.   Byte A unit of measure equal to eight bits of digital information. The standard unit measure of file size.     Calibration Setting equipment to a standard measure to produce reliable results.   CMYK (cyan, magenta, yellow, black) The subtractive primaries, or process colours used in colour printing. Black (K) is usually added to enhance colour and to print a true black.   Colour Proof A representation of what the final printed composition will look like. The resolution and quality of different types of colour proofs can vary greatly.   Colour Separation The division of an image into four separate colours for printing. Each colour is represented on a piece of film as lines of dots at specific angles. When overlaid, the dots on each level form tiny rosette patterns that simulate shades of colour when seen at a distance.   Crop Marks Lines that indicate the boundary of artwork. These marks are used to trim the page to its desired size after printing.     Densitometer A device sensitive to the amount of light transmitted or reflected by paper or film. It is used to check the accuracy, quality and consistency of output.   Density the degree of opacity of a photographic image on paper or film.   Dithering The process of specifying colour to adjacent pixels in order to simulate a third colour in a bitmapped image. This technique is used when a full range of colours is not available.   Dmax The highest level of density on a film negative.   Dmin The lowest level of density on a film negative.   Dot gain A printing defect in which dots print larger than intended, causing darker colours or tones.   Dpi (Dots Per Inch) A measure of the output resolution produced by printers, imagesetters or monitors.     Eliptical dot A type of halftone screen dot with an eliptical rather than circular shape, which sometimes produces better tonal gradations.   Emulsion The coating of light-sensitive material on a piece of film.   Emulsion Down This specifies a readable film image with the emulsion side facing away from the viewer. The printer usually decides whether emulsion should be up or down.   EPS (Encapsulated Postscript) A file format used to transfer Postscript image information from one program to another.     Film A transparent material coated with a light-sensitive substance.   Film Negative A piece of film with a reversed image, in which dark areas appear white, and vice versa.   Four-colour Process The use of cyan, magenta, yellow, and black in printing to produce a wide variety of colours.     Gamma The measure of how compressed or expanded dark or light shades become in an image.   Gamma Correction Compressing or expanding the ranges of dark or light shades in an image.   GCR (Gray Component Replacement) A technique for replacing all the neutral tones of an image with the appropriate amount of black.   Gradation A smooth transition between shades.   Grayscale The perceptible degrees of black below 100% coverage, usually 256 different shades.Grayscale monitors display distinct gray tones and one-bit black and white, and usually offer sharper images than colour screens.     Haltone Screen A pattern of dots of different sizes used to simulate a continuous tone photograph, either in colour or black and white.   Hard Dot A dot in a halftone screen that has smooth, crisp edges.   Highlight The lightest part of an image.   HLS A colour model based on three coordinates: hue,lightness (or luminance) and saturation.   HSV A colour model based on three coordinates: hue, saturation and value.   Hue A colour's wavelength of light in its purest state (without the addition of white or black).     Imagesetter A computer-controlled device used to output images at high resolution onto photographic paper or film.   Interpolation The addition of visual information calculated to fill in a range between points of existing data.     Kilobyte (K, KB) 1024 bytes of digital information. Abbreviated and referred to as K.   Knockout A shape or object printed by eliminating (knocking out) all background colours. Contrast to over-printing.     LAN (Local Area Network) A group of connected computers in a relatively small area that share access to printers and other peripheral devices.   Lpi (Lines Per Inch) A measure of the frequency of a halftone screen (usually ranging from 55-200). Lpi refers to the frequency of the horizontal and vertical lines.   Luminosity A value corresponding to the brightness of colour.   LUT (Look-Up Table) The table of available colours a computer uses to approximate a colour that falls outside of its range.     Mask The inactive area of a bitmapped image that will not respond to changes.   Megabyte (MB) 1024 kilobytes, or 1 048 576 bytes of digital information.   Moire An undesirable artifact produced in printing when halftone screen patterns become visible. Often caused by misaligned screens.   Monitor Calibration The process of correcting the colour rendition settings of a monitor to match selected colours of printed output.   Monochrome A black and white display with no gray tones.     Negative A piece of film with a reversed image, in which dark areas appear white, and vice versa.     PICT a common format for defining bitmapped or object-oriented images on the computer. The more recent format (PICT2) supports 24-bit colour.   Pigment Particles that absorb and reflect light and appear coloured to our eyes. The substance that gives ink its colour.   Pixel (Picture Element) The smallest distinct unit of a bitmapped image displayed on a screen.   PMS (Pantone Matching System) A commonly used system for identifying specific ink colours.   Posterisation The deliberate constraint of a gradation into visible steps as a special effect.   Ppi (Pixels Per Inch) A measure of the amount of scanned information. The finer the optics of the scanner, the higher the scan resolution.   Process Colours The four colours (cyan, magenta, yellow and black) that are combined to print a wide range of colours. When blended, these reproduce only a small portion of all the colours found in nature, but they can reproduce the widest range with the fewest inks when printing.   Proof A reasonable accurate example of how a finished piece is intended to look. Proofs can be in black and white or colour.     RAM (Random Access Memory) The memory a computer needs to store the information it is processing at any given moment. This is short-term memory and is lost when the power is shut off.   Rasterisation The conversion of image data into a pattern of dots, by an imagesetter for the production of negative or positive film or paper.   Reflective Densitometer Instrument used to measure the amount of light reflected by an image on paper.   Registration The alignment of different films or printing plates to produce one printed image.   Registration Marks Small cross-hairs on film used in the alignment of negatives.   Resampling An attempt to extract or add data without losing the characteristic properties of the data source, usually a scan.   RGB (Red Green Blue) The additive primary colours used for computer monitor displays. See also additive primaries.   RIP (Raster Image Processor) Part of an output device that rasterises information so that it may be imaged onto film or paper.   Rosette The pattern created when all four colour halftone screens are placed at the traditional angles.     Saturation The amount of gray in a colour. The higher the gray content, the lower the saturation.   Scanner A device used to digitise images to be manipulated, output, or stored on a computer.   Screen Angles The angles used to offset the different films in process colour separations. Proper screen angles are critical to minimize moire patterns.   Screen Frequency The number of lines of dots per inch on a halftone.   Soft Dot A halftone dot that exhibits a fringe or halo when viewed through a loupe, often caused by low-resolution image setting. This interferes with density readings and distorts the appearance of gradations.   Stochastic Screening An alternative to conventional screening that divides an image into very fine randomly placed microdots, rather than a grid of halftone cells.   Stripping The preparation and assembling of film prior to platemaking.   Subtractive Primaries The cyan, magenta, and yellow pigments used in printing to create different colours. Unlike the additive primaries, these produce darker colours when combined.     Targa (TGA) A file format for exchanging 24-bit colour files on PCs.   TIFF (Tagged Image File Format) A file format for exchanging bitmapped images (usually scans) between applications.   Transmissive Densitometer Instrument used to measure the amount of light that passes through an image on film.   Trapping A prepress technique which allows for variation in registration during the press run. On the desktop, this is done primarily by allowing an overlap between abutting colours.     UCR (Undercolour Removal) The removal of cyan, magenta and yellow percentages that make up a gray element within darker colours and replacing them with an appropriate amount of black.     Virtual Memory The process of using hard disk space as temporary storage in place of RAM. Used mostly for larger files, such as scanned images.