additive colours
Red, green and blue (RGB), the colours of light used in monitors and scanners, which give the perception of white when added together.

algorithm
A rule (often mathematical) governing computer processes; here, those used in file compression.

A-D Converter
The analogue to digital converter converts the analogue signal originating from the image sensor in a digital camera or scanner to a digital signal.

archival image
A digital image, also referred to as a master image, that has been captured at the highest practicable quality or resolution and stored for long-term usage. Archival images are normally stored in an off-line mode on tape or CD and are accessed only for the production of surrogate or derivative images.

area array
A common type of detector (see CCD and CMOS) arrangement within a digital camera; contains a fixed number of horizontal and vertical pixels.

artifacts
Visual digital effects introduced into an image by electrical noise during the capture process or over-compression that do not correspond to the original image being scanned. Artifacts might include pixellation, dotted or straight lines, regularly repeated patterns, moiré, etc.

autofocus
The camera automatically focuses on the object to capture at which it is pointed; this object then becomes the sharpest part of the overall image.

automatic sheet feeder
A device attached to a scanner, printer or photocopier that makes it possible to process large numbers of documents automatically.

bandwidth
The transmission capacity of a communications channel; data speed measured in bits per second. A high-bandwidth network is required for fast transfer of image files, as they typically contain large amounts of data.

benchmark
A set of tests normally done during the feasibility study, to determine the technical standards to which the material should be digitised. Quality assurance procedures should measure the digitized images against these benchmarks.

bit
Short for binary digit, the smallest unit of data in computer processing. A bit can represent two values: on and off, or 1 and 0.

bit depth
Also referred to as colour depth is the number of bits used to describe the colour of each pixel. Greater bit depth allows a greater range of colours or shades of grey to be represented by a pixel, e.g.:
- 1 bit is black or white (on or off)
- 8-bit grayscale is 256 shades of grey
- 8-bit colour is 256 colours
- 16-bit colour is 65,536 colours
- 24-bit colour resolution is 16.7 million colours
- 30-bit or higher colour is billions of colours

bit-map graphic
Also referred to as a raster graphic; a method of storing information that maps an image pixel. The bitmap image consists of rows of pixels.

BMP
Standard image format on DOS and Windows-compatible computers. The BMP format supports RGB, indexed-colour, greyscale, and bitmap colour modes.

brightness adjustment
The addition or subtraction of white light to a colour.

brightness resolution
Defines to what resolution a single pixel's intensity can be expressed

byte
A group of 8 bits, the basic unit of information for the computer.

calibration
The process of adjusting the colour of one device relative to another, such as a monitor to a printer, or a scanner to a film recorder, or the process of adjusting the colour of one device to some established standard.

capture devices
These include flatbed scanners, drum scanners, film scanners, digital cameras. They use electronic devices rather than photographic film to capture images.

CCD
Charge-Coupled Device; a light-sensitive chip or image sensor used in scanners and digital cameras that converts light into proportional (analogue) electrical current. The A-D converter converts analogue signals into pixel values.

CCITT Group III or Group IV
The standards adopted by the International Telecommunications Union (ITU), formerly the Comité consultatif international de télégraphique et téléphonie (CCITT), to compress text page images. All fax machines in common use employ one or both of these standards.

CD-ROM
Compact Disc Read-Only Memory. A form of write-once, disc-based, random-access data storage, usually mass-produced and distributed as a publication. At present, capable of holding approximately 640 megabytes of data.

CMD
Charge Modulated Device, an active image sensor derived from CCD pixel technology and CMOS transistor technology.

CMOS
Complementary Metal Oxide Semiconductor is another type of image sensor found in a digital camera. Pixel sensitivity is lower than the CCD sensors and usually has more noise in the imaging device.

CMS
Colour Management System; a collection of software tools designed to produce consistency in the representation of different colour capabilities of scanners, monitors and printers to ensure consistent colour throughout the image production process.

CMYK
A colour model using cyan, magenta and yellow pigments as the subtractive primary colours along with black (K), used primarily in the printing process. Combining the CMY inks at full saturation renders black (subtracting all colours).

colour accuracy
Fidelity of the scanned image's colour to that of the original.

colour correction
Altering colours as they appear in a digital image or in print to ensure that they accurately represent the work depicted.

colour depth
Also referred to as bit depth is the number of bits used to describe the colour of each pixel. Greater bit depth allows a greater range of colours or shades of grey to be represented by a pixel, e.g.:
- 1 bit is black or white (on or off)
- 8-bit grayscale is 256 shades of grey
- 8-bit colour is 256 colours
- 16-bit colour is 65,536 colours
- 24-bit colour resolution is 16.7 million colours
- 30-bit or higher colour is billions of colours

colour look-up table
A table containing the RGB values for 256 colours. Storage space is saved as an 8-bit number links each image pixel to a RGB value held in the table rather than having each pixel hold a 24-bit description of its colour.

colour scale
The relative values of all colours in a digital images. Used to ensure that colour representation is accurate and consistant from one digital image to the next.

colour separation
A process of converting full-colour images into a limited number of primary colors. Additive primary colours (red, green and blue) are used by the scanner, and the subtractive primary colours (cyan, magenta and yellow) plus black are used for printing press colour separation.

colour space
Mathematical definitions of colour used for aiding communication of colour information; means of representing the spectrum.

compactFlash
Storage card used in digital cameras to store captured images. The CompactFlash can be erased when the images have been transferred or are no longer needed.

compression
An algorithm applied to a digital image to reduce its file size. Compression techniques are distinguished by whether they remove detail and colour from the image. Lossless techniques compress image data without removing detail; lossy techniques compress images by removing detail.

continuous tone
An image whose brightness appears consistent and uninterrupted. Each pixel in a continuous-tone image file uses at least one byte each for its red, green and blue values. This permits 256 density levels per colour, or more than 16 million colours.

cropping
A method of discarding extraneous material from a digital image e.g. borders created during the scanning process.

derivative image
An image that has been created from another image, such as the archival image, through some kind of image editing process to create a user or working copy. The process usually involves a loss of information to reduce the size by sampling it to a lower resolution, using lossy compression techniques, or altering an image using image processing techniques.

descreening
Software functions build in to some scanning software applications to reduce or eliminate moiré patterning (unattractive stripes or diamond patterns appearing on the scan).

device driver
A software utility designed to tell a computer how to operate an external device: for instance, to operate a printer or a scanner, a computer will need a specific driver.

digital camera
A camera that contains no film but records images as digital objects which can then be downloaded into a computer for further processing.

digital image
A matrix or image composed of pixels whose locations hold digital colour and/or brightness information which, when viewed at a suitable distance, form an image.

digital imaging
A term generally used to describe the process of creating and manipulating digital images.

digital preservation
The long-term maintenance and upgrade of digital files on digital storage medium

digital watermark
A visible or invisible watermark that is applied to a digital image such that ownership of the image is known.

digital zoom
An electronic enlargement of part of the image making it appear closer and bigger, simulating a telephoto lens. The image is actually being cropped, resulting in loss of surrounding pixels and resolution. In some digital cameras and scanners, interpolation is used to offset this loss.

digitisation
Also referred to as image capture, is the process of creating a digital representation or image of an original through scanning or digital photography.

dithering
A process in which software or an output device simulates continuous tones with groups of dots.

DPI
Dots per inch; measurement of the scanning resolution of an image or the quality of an output device. DPI expresses the number of dots a printer can print per inch, or that a monitor can display, both horizontally and vertically.

drum scanner
A high-quality image-capture device. The image to be captured is wrapped around a drum that spins very fast while a light source scans across it to capture a digital version of the image.

dye sublimation
A type of printing process in which a dye ribbon is heated by the print head, creating a gas that hardens onto special paper. This creates soft-edged spots of colour that melt into each other and give the appearance of a continuous-tone photograph.

dynamic range
The ratio of the saturation to noise, limited by the bit depth of the sensor. Dynamic range is expressed numerically (3.0, for example). In the captured image the dynamic range relates to the colour fidelity and contrast range of the picture. The greater the dynamic range, the higher the contrast and colour bit depth.

file
A collection of information, such as text, data or images saved on a storage device such as a disk or hard drive.

file format
A type of format for encoding the information in a data file. Some common image file formats include TIFF, JPG, and BMP.

film scanner
Scanner specifically designed for capturing transparent film formats such as 35mm film by mounting film in a holder that may be automatically drawn through the device.

FireWire
A very fast external bus that supports data transfer rates of up to 400 Mbps developed by Apple, FireWire falls under the IEEE 1394 standard.

fixed focus
The camera's focus is pre-set to a distance at which most subjects or objects will be in focus. Not as precise as autofocus.

FlashPix
An image format developed by Kodak, Hewlett-Packard, Live Picture and Microsoft which offers multiple-resolution storage, and JPEG compression.

flatbed scanner
An image-capture device in which the source material remains stationary while the sensor (usually a CCD linear array) passes over or under it. Sometimes called a reflective scanner.

focal length equivalency
Lens specifications for digital cameras given in 35mm camera lens equivalents (since most users are familiar with 35mm lenses).

gamma
The relationship between the voltage input and the brightness of a monitor. An important factor in calibration as monitors have to compensate for gamma to get the desired on-screen grey values. The standard gamma on Windows is 2.2, and on Mac 1.8.

gamut
The total range of colours reproduced by a device. A colour is said to be "out of gamut" when its position in one device's colour space cannot be directly translated into another device's colour space. A typical CMYK gamut is generally smaller than a typical RGB gamut.

GIF
Graphic Image File format, a widely supported image-storage format promoted by CompuServe that gained early widespread use on online services and the Internet. Resolution is limited to 8-bits, or 256 colours. GIF89a is a more recent format that supports interlacing.

gigabyte (GB)
A measure of computer memory or disk space consisting of about one thousand million bytes (a thousand megabytes). The actual value is 1,073,741,824 bytes (1,024 megabytes).

greyscale
The brightness of a pixel expressed as a value representing it's lightness from black to white: Usually defined as a value from 0 to 255, with 0 being black and 255 being white. A term used to describe an image containing shades of grey as well as black and white.

halftone image
An image reproduced by means of a special screen made up of dots of various sizes to simulate shades of grey in a photograph; typically used for newspaper or magazine reproduction of images.

handheld scanner
A hand-held, generally low-quality, device for digitising images.

histogram
An analysis tool consisting of a bar graph that can be used to identify contrast and dynamic range image problems. Histograms are found in high-end imaging software used to manipulate digital images.

hue
Used to describe the entire range of colours of the spectrum; the component that determines just what colour is being used.

ICC
International Colour Consortium established by industry vendors to create, promote and encourage the standardisation and evolution of an open vendor-neutral, cross-platform colour management system architecture.

ICC device profile
A file that describes how a particular device (e.g., monitor, scanner, printer) reproduces colour in its specific colour space. Profiles can be either generic or custom.

image capture
Also referred to as digitisation, is the process of creating a digital representation or image of an original through scanning or digital photography.

image database
Computer system where image files are kept in an organised form. Software that facilitates organised storage and retrieval of digital images.

image formats
A type of format for encoding the information in a data file. Some common image file formats include TIFF, JPG, and BMP.

image manipulation
Modification of images such as tonal adjustments, cropping, moiré reduction, etc. using image editing software.

ImagePac
A widely used proprietary image file format developed by Kodak, designed specifically for storing photographic-quality images on CD.

image processing
Capturing and manipulating images to enhance or extract information.

image sensor
An electronic device capable of reacting to the impact of photons, converting them to an electrical current that is then passed on to the A-D converter. The most commonly image sensors used in digital imaging are CCD, CMD and CMOS.

indexed colour
Reduced colour mapping, 8 bit or less; done to reduce images to their smallest size. Commonly used for images placed on Internet pages. The 256-colour palette are also mapped for best results on the Internet, taking into account the differences between the Windows and Macintosh colour palettes.

inkjet printer
A type of printer that sprays dots of ink onto paper to create an image. Inkjet printers are normally inexpensive. Better-quality inkjet printers can attain near photo quality output.

interpolation
A process normally used in scanners and digital cameras to increase the image size in pixels by averaging the values of surrounding pixels.

ISO equivalency
The sensitivity rating for film or CCDs defined by the International Organization for Standardization (ISO). Digital cameras have fixed ISO equivalents or can be set to sensitivities ranging from 80 to 640 to achieve adequate exposure under different lighting conditions.

interface
A piece of hardware, a method, or a standard used for connection between or among computer devices.

Jaz drive
A computer disk drive made by Iomega that enables users to save about 1000 megabytes or 1 Gigabyte of information on their special disks.

JPEG
Joint Photographic Experts Group. Common format for displaying images on the Web. JFIF (JPEG File Interchange Format) is the actual file format used to compress an image with the JPEG method which is a standard developed for still-image compression sanctioned by the International Standards Organization (ISO).

jukebox
A peripheral device connected to a computer that can hold a number of optical disks or magnetic tapes at a time, making it possible to switch among them at will.

kilobyte (K)
An amount of computer memory, disk space, or document size consisting of approximately one thousand bytes: Actual value is 1024 bytes. Often used to refer to file sizes.

Lab colour
A colour model developed by the International Consortium on Illumination. The Lab model, like other CIE colour models, defines colour values mathematically in a device-independent manner. Lab colour is consistent colour regardless of the device producing it.

laser printer
A printer using laser copier technology to produce high-quality printed material from computer data. The laser charges an electrostatically sensitive drum to accept carbon-based toners which are then transferred and fused to paper or transparency material.

LCD monitor
The liquid crystal display colour screen on most digital cameras, usually 1.8 to 2.5 inches measured diagonally; used to check images after they are shot. The LCD monitor is usually more accurate than an optical viewfinder, though not as convenient to use.

lossless compression
A compression algorithm that reduces the storage space needed for an image file without real loss of data. The uncompressed image can be reconstructed to be identical to the original. Continuous-tone images will on the average be reduced to half the original size.

lossy compression
A compression algorithm that reduces file size by actually removing data from the image. The most effective lossy-compression algorithms work by discarding information that is not easily perceptible to the human eye. Effective compression ratios of 10:1 to 50:1 can be attained.

LPI (lines per inch)
The number or density of horizontal and vertical lines in a halftone screen.

LZW
Lempel-Ziv-Welch is a proprietary lossless data-compression algorithm used in GIF and TIFF files.

macro lens
A digital camera lens mode that allows one to get very close to objects so that they appear greatly enlarged in the picture.

manual focus
Digital camera focus that can be manually be set at any point from near to far or in steps such as 3 feet, 15 feet, or infinity. Also provided as an override feature on some autofocus.

master image
A digital image, also referred to as a master image, that has been captured at the highest practicable quality or resolution and stored for long-term usage. Archival images are normally stored in an off-line mode on tape or CD and are accessed only for the production of surrogate or derivative images.

megabyte (MB)
An amount of computer memory consisting of about one million bytes: The actual value is 1,048,576 bytes.

megapixel
The measure of the resolution of a digital camera with an image sensor capable of capturing one million pixels.

memory
Commonly used to refer to a component in a electronic system that stores information for future use.

metadata
Data about data, or information known about the image in order to provide access to the image. Usually includes information about the intellectual content of the image, digital representation data, and security or rights management information.

migration
Preserving the integrity of digital images by transferring them across hardware and software configurations and across subsequent generations of computer technology as a means of preservation and access.

moiré
A visible pattern that occurs when one or more halftone screens are misregistered in a colour image.

multi-megapixel
The resolution of a digital camera with an image sensor capable of capturing two million pixels or more.

noise
Data or unidentifiable marks that may appear as bright specks in dark areas of a scan owing to electrical interference in the CCD sensor and associated circuitry.

OCR
Optical Character Recognition. The technology that allows computers to 'read' text from physical objects. OCR requires a graphical representation of text to interpret, which usually comes from a scanned image.

optical resolution
The true resolution of an image sensor based on the number of photosites on the surface of the image sensor without recourse to interpolation.

optical viewfinder
An optical glass device on the digital camera which, when looked through, shows the image to be photographed. The best digital cameras have both optical viewfinders and LCD monitors.

optical zoom
A zoom lens that uses movement of lens elements to achieve various fields of view. Regardless of whether the zoom is set for wide angle or telephoto viewing, the resolution of the image remains the same.

palette
The set of colours that appear in a particular digital image. Becomes part of a colour look-up table.

PCX
Image file format commonly used by IBM PC-compatible computers.

photographic film
Substrate coated with emulsion containing light sensitive silver halide grains.

PhotoCD
Compact disk-type storage technology developed by Kodak. Five levels of image quality are stored for each image in an Imagepac on a PhotoCD disc.

PhotoShop
PhotoShop is a widely used image editing application from Adobe, often used as a benchmark for other imaging applications.

photosite
A small area on the surface of an image sensor that captures the brightness for a single pixel in the image. There is one photosite for every pixel in the image.

PICT
A graphics file format widely used among Macintosh graphics and page-layout applications as an intermediary file format for transferring files between applications.

pixel
Short for picture element; the smallest unit that makes up an image. Each pixel can represent a number of different shades or colours, depending on how much storage space is allocated for it. Also used in measuring image size and resolution.

pixellation
Occurs when an image is enlarged (by zooming in) as each pixel in the image will take up two (or more) pixels on the display. This leads to the image having steps on edges that are anything other than horizontal or vertical. Also referred to as 'jaggies'.

PNG
Portable Network Graphics; a standard file format approved by the World Wide Web consortium to replace the GIF file format. PNG is patent and license-free.

PostScript
A page description language developed by Adobe Systems, Inc. to control precisely how and where shapes and type will appear on a page. Software and hardware may be described as being PostScript compatible.

PPI
Pixels per inch; measurement used to describe the size of the final printed image. An image that has a higher number of pixels per inch will show more detail than one which has fewer pixels per inch.

quality assurance
Also referred to as quality control; the monitoring of systems and processes to ensure that the quality of work is within defined tolerances.

RAM
Random Access Memory; the volatile memory used to store information temporarily during processing. RAM is used in most processors in computers, digital cameras, printers, etc.

raster graphics
Also referred to as bitmap images; an image composed of pixels or an image represented with a matrix of dots.

refreshing
Transferring digital data to new storage media to avoid the effects of media deterioration.

resampling
Changing the resolution of an image by increasing or decreasing the number of pixels.

resizing
To alter the resolution or the horizontal or vertical size of an image.

resolution
Spatial resolution, normally expressed as the number of pixels per linear unit e.g., 300 ppi (pixels per inch), sometimes dpi (dots per inch) or spi (samples per inch). For colour resolution see Bit Depth.

RGB
An additive colour model in which red, green and blue light is combined to create colours, combining full intensities of all three makes white. Digital cameras, scanners and monitors use RGB to record and display colours.

RLE
Run Length Encoding is a lossless compression format primarily used with Windows files (BMP, PCX). RLE supports only 256 colours.

ROM
Read Only Memory; memory that can be read but not updated or changed. Memory that is nonvolatile and does not disappear when power is shut off. Commonly used in computers and CD formats such as CD-ROMs.

scan area
The maximum dimensions of the area in a flatbed scanner in which an original can be placed for scanning.

scanner
A device for capturing a digital image. There are many types of scanners, such as flatbed scanners, drum scanners, film scanners and microfilm scanners.

scanning area array
A hybrid of scanning linear array and area array used to describe the arrangement of the detector within a digital camera.

scanning linear array
A way in which the detector within a digital camera can be arranged resulting in high resolution images.

SCSI
Small Computer Serial Interface. A system of connecting a chain of computer peripherals to a computer.

serial port
A data transfer method used to connect a peripheral, such as a digital camera, to a computer. The serial connection will allow the peripheral to transfer data to the computer and vice versa.

sharpening
A software method of exaggerating edges in an image to give enhanced definition.

software
Written coded commands that tell a computer what tasks to perform. For example, Word, PhotoShop, Picture Easy, and PhotoDeluxe are software programs.

spatial resolution
Describes how much detail in a photographic image is visible to the human eye. High-resolution images are sharp and more details are visible.

storage device
A device such as a magnetic disc, CD or tape used to store and retrieve digital files.

subtractive colours
The colour pigments cyan, magenta and yellow (CMY), which produce black when mixed in certain amounts. In printing, black is often added to give more definition, as mixing of actual inks cannot produce pure black.

surrogate image
A digital image derived from the archival Image. Usually not as high resolution as the archival image, surrogate images are usually used as output images on display devices or printers.

thumbnail image
Small, low-resolution preview image, often linked to a high-resolution version of the same image.

TIFF
Tagged Image File Format is an image file format used extensively for the storage of high-quality images.

transparent media adaptor
Part of a flatbed scanner used when scanning film or transparent media that allow light to pass through the media during the scanning process. Usually an optional extra.

true-colour image
A 24-bit image.

TWAIN
An acquire interface developed by a consortium of software developers as a standard for communications between scanners, imaging devices and now digital cameras and the computer software.

USB
Universal Serial Bus, a device allowing for easy connection of serial devices to PC. The aim of USB is to eliminate the serial port bottleneck that has plagued PCs since the beginning. Many newer peripheral devices such as digital cameras and scanners support USB.

vector graphic
An image composed of individual elements, e.g., arc, line, polygon, with their own attributes that can be individually edited. A drawing-type package is usually required to display such vector images.

watermark
Bits altered within an image to create a pattern that indicates proof of ownership. Unauthorized use of a watermarked image can then be traced.

white balance
How the colour white is reproduced. On a monitor the white point is the combination of all three red, green and blue phosphors at full intensity, as measured by its colour temperature in degrees K. It is used as a reference point in calibration.

WORM
Write Once; Read Many; refers to data storage that cannot be changed once written, though it may be read as many times.

YCC
A colour encoding scheme developed by Kodak for its Imagepac file format.

ZIP
A ompression format. Files compressed with PKZip or WinZip are the most common archive format.

zip drive
A computer disk drive made by Iomega that enables users to save about one hundred megabytes of information on their special disks.