additive primaries - Another name for Red, Green, and Blue. Called additive because when all three are combined they create pure white.

aliasing - See jaggies.

analog - Continuously variable signals or data. As opposed to digital. 

bit - Binary Digit. The basic unit of information that all computers use to manipulate data. The value of a bit (0 or 1) represents a two-way choice, such as yes/no, on/off, or black/white. 

bit depth - The amount of tone data per sample expressed in number of bits. Typical bit depths are 1 (for line art), 8 (for grayscale), and 24 (for color images). 

bitmap - Originally a term used to describe a memory model where each bit in screen memory was "mapped" to a corresponding screen pixel, hence the term bit-mapped. Today it is used universally to describe all manner of pixel oriented displays, from 1-bit (true bitmapped) to grayscale (8-bits per pixel) to full color (16 or 24-bits per pixel). 

black point - See shadow point. 

brightness - The intensity of light reflected from a print, transmitted by a transparency, or emitted by a pixel. 

byte - A computer term equal to 256 levels of information (28). Also, the number of bits used to represent a character. 1 byte equals 8 bits. A standard unit of measure for file size. See kilobyte, megabyte, gigabyte, and terabyte. 

CCD - Charged-Coupled Device. A light sensitive electronic device that emits an electrical signal proportional to the amount of light stricking it. Used in scanners and video cameras.. 

CIE - Commission Internationale l'Eclairage. An international standards committee that defined the de facto standard color model used in all color management systems. 

CD-ROM - Compact Disc-Read Only Memory. A CD-ROM drive uses the CD (compact disc) format as a computer storage medium. One CD can store approximately 640 megabytes of data and other mixed media on a disc about the size of a traditional 5-1/4-in. floppy disk. 

channel - Analogous to a plate in the printing process, a channel is the foundation of a computer image. Some image types have only one channel , while others have several, with up to16 channels. 

CMS - Color Management System. A comprehensive hardware/software solution of maintaining color fidelity of an image from scanner to monitor to printer. 

CMYK - Cyan, Magenta, Yellow, Black. The subtractive primary colors, also known as process colros, used in color printing. See subtractive primaries 

color cast - The effect of one color dominating the overall look of an image. Often caused by improper exposure, wrong film type, or unusual lighting conditions when shooting the original image. Also caused, when scanning, by the sometimes unpredictable interaction between an image and a scanner. 

color separation - An image that has been converted or "separated" from RGB into the four process colors. See CMYK. 

compression - Algorithms used to create smaller file sizes of stored images. There are two kinds of compression: Lossless and Lossy. 

contrast - The difference in brightness between the lightest and darkest tones in an image. Also, a steep region in a tone curve. 

crop - To permanently discard unwanted information in the perimeter area of an image. 

DCS - Desktop Color Separation. A five-file EPS file format consisting of four high-resolution color separations and a fifth position-only file for placement within documents. 

decompression - The opposite of compression. Decompressed images are as big and have the same resolution as the original image was before being compressed. 

default - The settings in a computer program which will take effect if no changes are made. 

density - The measure of light blocking (in the case of transparencies) or absorption (in the case of prints), expressed logarithmically. Typical slides have a density of 3.0 while typical prints have a density of 2.0. 

descreening - The technique of eliminating moiré patterns when scanning. 

digital - Discrete data made up of steps or levels. As opposed to analog. 

dithering - A technique of using patterns of dots or pixels to create the effect of an intermediate tonal value. 

Dmax - The Maximum Density in an image. See Shadow point. 

Dmin - The Minimum Density in an image. See White point. 

dot gain - The effect of ink spread and absorption into paper during printing resulting in darker tones, especially midtones 

DPI - Dots Per Inch. A measure of the output resolution produced by laser printers or imagesetters. See also LPI. 

driver - A small software module that contains specific information needed by an application to control or "drive" a peripheral such as a monitor, scanner, or printer. 

drum scanner - A high-end scanning device, utilizing PMT technology, used to digitize prints, transparencies, and artwork. 

EPS - Encapsulated PostScript. A subset of the PostScript page description language that allows any single-page artwork, be it line art or image data, to be saved and placed into any other EPS compatible document. See also DCS. See PostScript.

EPS 5 - Another term for DCS 

exposure - Defines the overall brightness of an image resulting from a combination of time and intensity of light allowed to the film. 

file - A named collection of binary information stored as an apparent unit on a secondary storage medium such as a computer disk drive. 

film recorder - A device that renders digital data onto analog film. Typical film sizes are 35mm and 4x5. 

flatbed scanner - A popular type of desktop scanner so called because of its glass platen, or "bed", upon which originals are placed to be scanned. 

FPO - For Position Only. Typically a low-resolution image positioned in a document only to be replaced later with a higher resolution version of the same image. 

frame grabber - A device that captures and digitizes a single frame of a video sequence. Typical resolution is 640x480 samples. 

gamma correction - The measure of contrast that results in lightening or darkening the midtone regions of an image. Also, the amount midtones need to be adjusted on a monitor. 

gigabyte - Equivalent to exactly 1,073,741,824 bytes of information (230). 

grayscale - A continuous tone image made up of a number of shades of grey. See monochrome 

halftone - A technique of converting a continuous-tone (grayscale) image into variable sized spots representing the individual tones of the image. 

halo - A consequence of using too high a setting of radius in unsharp masking. The effect is one of a light region surrounding the perimeter of a darker region. 

hard disk - A secondary storage medium for computer files. A place to store your scanned images. 

high key - An image that is primarily composed of light tones. 

highlight - The lightest desireable tone in an image. The tonal value in an image above which all tones are rendered pure white. See Dmin and white point. 

histogram - A graphic representation of the number of samples corresponding to each tone in an image. See tone curve 

hue - The main differentiating attribute of a color. The wavelength of light which represents a color. 

icon - In a graphical user interface, an on-screen symbol that represents a program file or computer function. 

imagesetter - A high-end device for taking rasterized data (See RIP) and exposing film used for printing processes. 

interpolation - The technique of estimating the tonal value that lies between two known tone samples. Used for enlarging an existing image. Also used when capturing an image during the scanning process to achieve higher than optical resolution. 

inverting - Creating a negative of an image. 

IT8 - An industry standard color reference target used to calibrate scanners and printers. Many color management systems use IT8 targets. 

jaggies - The pixelated or stairstepped appearance of low-resolution computer-generated images. 

JPEG - Joint Photographic Experts Group. An industry standard lossy form of compression for image data. JPEG offers one of the best compression schemes available. 

kilobyte - Equivalent to exactly 1024 bytes of information (210). 

laser printer - A printing device using electrostatic toner to create an image derived from page description information. 

line art - Images comprised of only pure black and white data. Also a mode of capturing such images. 

lossy - A technique of compressing an image by eliminating redundant or unneccesary information 

low key - An image that is primarily composed of dark tones. 

LPI - Lines Per Inch. A measure of the frequency of a halftone screen used in printing. The archaic, and now misleading term line harkens back to the diffraction line etchings used to create analog halftones 

LZW - Lempel-Ziv-Welch. A popular, lossless image compression algorithm. 

matrix - A grid of horizontal and vertical cells. e.g. Video cameras use a matrix of CCDs. 

megabyte - Equivalent to exactly 1,048,576 bytes of information (220). 

midtone - The range of tones in an image located approximately halfway between highlights and shadows 

modem - MOdulator/DEModulator. An electronic device used to convert a computer's digital signal to an analog one and vice versa. The result is a signal that is capable of being transmitted over telephone lines. 

moiré - An undesirable interference pattern in color printing often resulting from misaligned or improper screen angles. Also created when previously halftoned images are scanned. 

monochrome - An image comprised of various shades of one hue. See grayscale. 

monitor - The device that produces an on-screen display. Synonymous with video display unit. There are three types of monitors: black and white, grayscale, and color. 

Newton Rings - A pattern of concentric, multi-colored rings occasionally introduced in a scanned image by contact of transparency film with the glass platen in a scanner. 

noise - Extraneous or random samples introduced into a scanned image via the electronic components of a scanner. 

OCR - Optical Character Recognition. Software that uses pattern recognition to distinguish character shapes in a bitmapped image. Typically used with scanners. 

offset lithography - A commonly used printing process utilizing an intermediate blanket cylinder to transfer, or "offset" an image from the plate to the paper. 

optical resolution - The true number of discrete samples per inch that a scanner can distinguish in an image. 

over sampling - Scanning an image at a higher than 8 bits per channel. Used for high-end image manipulation ‹ greater bit-depths allow for greater image fidelity. Available from mid- to high-level scanning equipment. 

over scanning - Scanning an image at a higher resolution than is necessary. Used for archiving images for later use. 

PICT - A Macintosh-based format for storage and exchange of graphic documents, containing bitmap and/or object-based images. 

pixel - Picture Element. The individual elements that comprise a video monitor's image area. Typical monitor pixel resolutions are 640x480, 800x600, 1024x768. 

platen - The glass scanning region on a flatbed scanner. 

PMT - Photo Multiplier Tube. The kind of technology used in Drum scanners. 

PostScript - A robust, general purpose page description language which has become the defacto standard in the prepress industry. Used in most all imagesetters and many laser printers. 

PPI - Pixels Per Inch. The frequency of the number of samples used to display an image on a computer monitor. 

prescan - A quick, low resolution preview scan of an image to be scanned. 

primary color - A base color used to create other colors. Examples are Red, Magenta, Green, Yellow, Blue, and Cyan. Also loosely used to describe any highly saturated color. 

profile - The compiled color characteristics of a known device, such as a monitor or scanner, as used with a color management system. 

process color - The CMY primary colors (plus black) used in printing to produce the widest spectrum of printable colors. See also color separation. 

quarter tones - Tones in an image that lie between between midtones and highlights. Three quarter tones are tones between midtones and shadows. 

RAM - Random Access Memory. The memory a computer needs to store the information it is processing at any given moment. Because RAM is short-term memory, it is lost when the power is shut off. The larger the amount of RAM, the larger the size of files that can be processed and the greater the speed with which they can be processed. 

raster - A bit mapped representation of data. See RIP. 

resample - To change the resolution (and the resulting file size) of an image. Resampling to a higher resolution introduces more data through interpolation. 

resolution - The output measurement of an image, expressed in dots per inch (dpi), pixels per inch (ppi) or lines per inch (lpi) 

RGB - Red, Green, Blue. The additive primary colors used in computer monitors and image recorders. 

RIP - Raster Image Processor. The software/hardware device that interprets output data (such as page description information) to create a bitmapped image comprised of output dots and deliver that image to a print engine. 

sample - The smallest, discrete amount of data captured by a scanner. Expressed in bit-depths of 1, 8, or 24 bits. 

saturation - The amount of grey in a color. Less grey results in more saturation. 

screen frequency - See Halftone, LPI 

SCSI - Small Computer System Interface. A standard that allows communication between computers and peripheral devices. 

separations - See color separations 

shadow point - The samples in an image that will print the darkest tone possible of the intended output device. Tonal values below this will print pure black. See Dmax.

sharpening - A technique of accentuating the contrast between all areas of tonal difference within an image. 

spectral highlight - Pure white with no tone. Spectral highlights within an image should not be used for Set Whitepoint. 

SPI - Samples Per Inch. Used here to indicate the number of data points per inch that a scanner captures (i.e. input). As opposed to DPI (dots per inch), PPI (pixels per inch), or LPI (lines per inch) - all of which refer to output. 

subtractive primaries - Another term for Cyan, Magenta, and Yellow. Called subtractive because when all three are combined they absorb all light (theoretically) and create black. See CMYK. 

terabyte - Equivalent to exactly 1,099,511,627,776 bytes of information (240). 

threshold - The tonal value ‹ used when scanning line art or converting grayscale images to bitmapped ‹ above which is rendered white and below which is rendered black. Typically expressed in percentage of grey. 

TIFF - Tag Image File Format. A popular file format used for storing images. TIFF formats support a wide range of color models and bit depths. 

TWAIN - Unofficially "Technology Without An Interesting Name" -- really! A "mostly" PC standard software interface enabling compatibility between scanning software and scanning hardware. 

tone curves - A linear graphic representaion of the mapping of input tones to output tones. See histogram 

unsharp masking - Also known as USM. A technique of accentuating the contrast at border areas of significant tonal difference within an image. With proper controls, USM will only sharpen areas of important detail. See sharpening 

white point - The samples in an image that will print the lightest tone possible of the intended output device. Tonal values above this will print pure white. Not to be confused with Spectral highlight. See Dmin.