{1}{2}Automatic Document Feeder (ADF)

An optional device available for some desktop scanners which enables 'hands-off' operation when you are scanning a large number of pages sequentially.
{3}bitmap

A generic term used to describe a computer-stored image composed of pixels, especially a black and white one.
{4}CD-R (Compact Disc Recordable)

Also called Writable CD.  A type of compact disc which can be recorded once only (see WORM) using special discs and recorders, but which can be read in a conventional CD player or CD-ROM drive.
{5}CD-ROM (Compact Disc Read-Only-Memory)

A type of compact disc used for storage of digital computer data instead of music or speech.
{6}CD-ROM (Compact Disc Read-Only-Memory)

A type of compact disc used for storage of digital computer data instead of music or speech.
{7}Charge Coupled Device (CCD)

A type of solid-state sensor used in scanners and video capture devices.
{8}CMYK

A colour model which defines all possible colours in percentages of Cyan, Magenta, Yellow and Black.  This is the colour model used for printing images.

{9}colour correction

A process which can be performed by single pass scanners or by scanning software to adjust the colour shades in a colour image to optimise it for a particular type of output device.

{10}Computer Aided Design (CAD)

A technique for producing engineering and architectural drawings on a computer using line oriented techniques.

{11}contone

A continuous tone image (colour or monochrome) such as a photograph.

{12}DeskTop Publishing (DTP)

The term used to describe the process of using computer software to make up pages of text and graphics for use in publications.

{13}digitiser

A device which converts analogue data to numeric format and can be used to capture still frames from a video film.  Sometimes also called a video grabber.

{14}dithering

The process of grouping dots shown on your monitor or produced by a printer into clusters of varying sizes to simulate varying shades of grey or colour tones.  Many desktop scanners incorporate various software dithering techniques for use with different output devices.

{15}Document Image Processing (DIP)

A way of scanning whole pages, usually as greyscale images, and saving them on file.  Complete libraries of documents can thus be stored for later retrieval using computerised indexing.

{16}Dots Per Inch (dpi)

A measure of the resolution of an image, expressed in the number of pixels or printed dots in an inch.

{17}dropout colour

A colour (red, green or blue) which you can instruct your scanner to ignore when scanning in monochrome.  This facility is useful for removing coloured mark-up from a page or for scanning a page which has a coloured background.

{18}flopticals

Disks which are similar to floppy disks in appearance, but which can hold far greater amounts of data.  The name floptical is a corruption of 'floppy optical'

{19}fractal compression/transformation

a way of analysing an image to determine how it can be represented mathematically as a sequence of complex expressions instead of bitmap data.

{20}full colour image

see true colour image

{21}Gamma correction

A way of adjusting the Gamma curve of an image (see next entry) so that the reproduction results on different types of output device have similar gradations as the original image.

{22}Gamma curve

A graph which shows the contrast ratio between the input (original image) and output (image data) in image processing.

{23}greyscale

The spectrum of different grey levels in an image - usually up to 256.  It is also used to describe the number of intensity levels of a particular colour component of an image, again usually 256.

{24}halftone

A continuous tone image reproduced using an array of various sized dots to create the illusion of tone.  Most newspaper images are halftones.

{25}halftone cell

The name sometimes given to a cluster of printer dots produced by dithering a halftone image for printed output (see dithering).

{26}halftone line screen

A pattern of dots or lines used in the creation of a halftone from a continuous tone image.  Halftone line screens are measured in lines or dots per inch - usually between 35 and 150 lpi.  The higher the line screen value, the greater the number of dots per line or inch.

{27}HSL (Hue, Saturation and Lightness)

A colour model which defines all possible colours by specifying a particular hue and then adding or subtracting percentages of black or white.  Also known as the Hue, Saturation and Brightness model.

{28}HSB (Hue Saturation and Brightness)

see HSL

{29}interpolation

A facility built into many scanners for doubling the resolution available by calculating the appropriate colour value for pixels positioned in between those actually scanned.

{30}JPEG (Joint Photographic Experts Group)

This group was set up to devise an ISO-CCIT standard for image compression algorithms including both lossy and non-lossy techniques.  However the term is most often used to describe the standard for non-lossy compression which is supported by a number of software products.

{31}JPEG (Joint Photographic Experts Group)

This group was set up to devise an ISO-CCIT standard for image compression algorithms including both lossy and non-lossy techniques.  However the term is most often used to describe the standard for non-lossy compression which is supported by a number of software products.

{32}line art

Images which are composed only of black and white lines (e.g. a technical drawing).

{33}line screen

see halftone line screen

{34}lines per inch (lpi)

The usual measure of halftone resolution.

{35}Optical Character Recognition (OCR)

The process of converting printed characters into the actual ASCII characters and other attributes of a bitmap image of text.

{36}optimised palette

A colour palette (see palette colour image) which has been chosen  by analysing the original full colour image to determine the most suitable combination of shades to use in the palette.  A palette colour image created using an optimised palette will be closer to the original in appearance than one created using a fixed palette.

{37}lossy compression

A form of data compression which may distort or 'lose' some of the original pixels in the image in order to improve the compression ratio.

{38}Moiré effects

The name given to interference patterns which may arise when two or more halftone screens are at odds with each other.

{39}non-lossy compression

A way of compressing data (in this case image data) without losing any of the original information in the image.

{40}optical resolution

The actual physical resolution of the scanning hardware before any interpolation or zooming functions are used.  The optical resolution of a typical desktop scanner is 300 or 400dpi, but most scanners use interpolation to effectively double the resolution available to the computer - see interpolation.

{41}palette colour image

An image in which each pixel is one of a limited number of colour shades.  Selected colours are chosen from a larger range of shades (often over 256,000) to form a 'palette' of a smaller number of shades (often 256) which are the only ones used in the image.  A mapping table is stored with the image to identify which shades are used in the image.

{42}Photo CD

A CD format developed by Kodak for storing bitmap images on a CD-ROM in a convenient and accessible form.

{43}pixel

A picture element of a screen image - one dot of the collection which makes up the image.

{44}resolution

The density of dots or pixels on a printed page or display, usually measured in dpi.

{45}RGB colour model

A colour model which defines all possible colours as percentages of Red, Green and Blue.  This model is used by scanners and by CRT displays.

{46}SCSI interface

A SCSI interface (Small Computer Systems Interface) can transmit large amounts of data at high rates, making it ideal for scanning and image-editing work.

{47}single pass scanning

A mode of colour scanning in which the original is scanned in one pass of the scanner carriage.

{48}three pass scanning

A mode of colour scanning in which the original image is scanned in three passes of the scanning carriage.

{49}transparency adapter

An optional unit sometimes available for desktop scanners which enables the scanner to use transparent rather than reflective materials.

{50}true colour image

An image stored using 24 or 32 bits per pixel which allows representation of over 16.7 million different shades in the image - also called full colour.

{51}TWAIN

A high-level programming interface for 'image acquisition devices' - typically scanners.  It was developed jointly by Caere, Aldus, Hewlett-Packard, Logitech and Kodak.

{52}vector images

Images defined as series of straight lines.  The beginning and end-points of each line are stored and can be adjusted if the image needs resizing.

{53}video grabber board

A device which converts analogue data to numeric format and can be used to capture still frames from a video film.  Sometimes also called a digitiser.

{54}WORM (Write-Once-Read-Many)

An optical disk technology which allows the user to write data to the disk, but not to erase or modify data which has already been written - see CD-R.

{55}zoom

A facility built into many scanners for increasing or reducing the image size, by recalculating lines in the image with a greater or fewer number of pixels, using the data actually scanned as a reference.  The technique is similar to interpolation but will usually be slightly less accurate.  Zooming can be used in conjunction with interpolation to achieve extra high resolutions, but this is only recommended when scanning line art.

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