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Glossary of Digital Photographic Terms

Digital Glossary

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.

A

• AD — Analog-to-digital.
• Adapter (card)—There are a variety of memory card formats produced by different manufacturers. They may be referred to as ATA cards, or by their various proprietary names such as Smartmedia, Memory Sticks, Compact Flash, SD, or film cards. These various devices may require an adapter to be used for reading in a computer or maybe be addressable via USB or fire wire or built into the CPU.
• ADC—Analog-to-digital converter.
• A/D Converter—Analog-to-digital converter. A scanner or other device that converts analog subjects, such as continuous-tone photographs, into a series of numbers or on–off (digital data) that can be processed, stored, and manipulated by a computer.
• Address—A name or numeral that designates a particular location in computer memory.
• Addressable resolution—In electronic imaging, the maximum number of locations addressable at one pixel per location.
• Algorithm—In computers, an algorithm defines the number of steps or the extent of the process required to solve a coding problem. It is a structured, step-by-step course of action.
• Aliasing—Low- and medium-resolution computer-imaging systems display normally smooth edges as jagged edges. These jaggies are known as aliasing. It may result from undersampling the spatial frequency, or when the detail exceeds the display ability of the monitor.
• Alpha channel—Unused 8-bit portion of a 32-bit image. It can be used as a mask to apply filters, changes, or overlay graphics on top of an image. The alpha channel can be used to control the opacity of the image.
• Amplitude—(1) The size dimension of a waveform, usually represented graphically in the vertical plane. The size represents the strength of the unit being measured; for example, sound pressure level for sound. (2) The strength of an analog signal. In computer imaging, it is the voltage level that represents a brightness of a given point in the image.
• And/or—In computers, the logical operators are generally part of the arithmetic logic unit (ALU). It provides for the combining of two images pixel by pixel. The and function is used to mask off a portion of the image. The or function is used to add sub-images into a composite output.
• Antialiasing—A computer algorithm designed to smooth jagged edges in an image. This can be accomplished by blending an object with its background in a smooth transition. This technique is often used to accomplish the appearance of smooth, large text on a display.
• Anti-virus — A software designed to identify and or reject “diseased” software covertly placed into a computer. The virus is designed to disorient, slow down, or “kill” the computer’s operating system or data files or the hard disk’s directory.
• Application — A computer program written for a specific purpose such as a graphics or word-processing program. Area array—This is a method of pixel organisation in a charge-coupled device (CCD). In this method, pixels are located both in the horizontal as well as vertical orientations (x, y matrix). A finite number of pixels will exist in each direction dictated by the manufacturing of the CCD.
• Arithmetic Logic Unit (ALU)—A component found on the computer motherboard that performs multiplications, additions, or logical operations on data, including images.
• Array—The holding of the image in a two-dimensional (x, y) configuration. This structure or matrix on the y axis equals the number of lines that makes up the image. The x axis equals the number of pixels per line.
• Array processor — Specific computer hardware designed to hold the image in the form of a two-dimensional array. Such devices are “hung onto” the central processing unit (CPU). The device allows for fast image processing. Some array processors have built-in algorithms for specific image processing.
• ASCII — American Standard Code for Information Interchange, a byte coding for the standard character set used by most computers; used to transfer text files between computers. [Files are written in the code without any formatting commands and has not been updated since 1987.]

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B

• Backing up—In the event of a system failure, a backup operating system and backup files are used to restart the system. Backing up generally refers to making copies of the startup software (operating system) and important applications and data files.
• Back porch — In video recording, a brief blackout period between the horizontal sync pulse and the start of picture data. This blackout period is considered to be blacker than black. The setting allows for the distinction between a picture signal that is black and the black resulting from no signal.
• Baud rate — The speed of data transmission, usually equivalent to bits per second. Many data transmission protocols support 300, 1200, 2400, or 9600 baud rates over standard telephone lines. Dedicated local area network lines can support baud rates at about 19,200 baud. The higher the baud rate, the more data can be transmitted in the same time. A greyscale, low-resolution image would transmit in approximately 2.2 minutes at 19,200 baud as compared to a trans- mission time of approximately 34.2 minutes at 1200 baud.
• Bit — A contraction for the term binary digit. A bit is the smallest unit of data transfer. As a basic unit it represents an off (0) or on (1) state. In imaging, the more bits, the more tones that can be displayed in a digitised image. A 8- bit image can display 128 tones including black and white. A 3-bit image can only display a total of 8 tones.
• Bit depth—Bit depth refers to the number of shades of grey that an image can display and is assigned to each pixel. The more bits the greater the tonal range possible. For example, a greyscale image that is an 8-bit image will display 256 different tones.
• Bitmap — A pixel-by-pixel description of an observable image. When the resolution is high enough, the image is seen as a continuum; however, when there is insufficient data, there will be the appearance of image pixels or picture elements.
• Bit plane—The storage of graphical images including text as a graphical representation. The image is stored in random- access-memory (RAM) as a pattern of bits in the sequence in which they are scanned (rastered), thus representing the image.
• Blurring — In computers, the attenuation of high-frequency information in the image through the use of neighborhood averaging. The strength of the blur is determined by the size of the kernel. This technique may be used to remove patterned noise.
• Board — Generally, in the DOS world a board is a device that plugs into a bus slot to perform a specific task, such as accelerating graphics, driving the monitor, controlling hard and floppy disks, or digitising video and sound. In the Macintosh world, boards are generally referred to as cards.
• Boot—To start up a computer. If the computer is off, this is known as a cold boot. If the computer is on but not operating, a warm boot (restart) is performed.
• Brightness resolution—The luminance contrast range that a pixel is capable of providing. The higher the resolution, the greater the number of grey levels or tones that are capable of being reproduced. This is also referred to as pixel depth or number of bit depth.
• Buffer memory — An intermediate location in an electronic imaging system. A system with a large buffer memory will allow faster functions such as acquisition, reading, and writing to occur. More advanced systems will have greater function in this system feature.
• Bug — An error or malfunction in hardware or software that causes the computer to abort. The term results from the actual discovery of a moth in a Mark I computer’s electronic relay. The removal of the moth gave rise to the term debugging.
• Byte—A group of 8 bits. Bits are moved about the computer in groups. These groups may be 8 bits (a byte), 16 bits (2 bytes), or 32 bits (4 bytes). The greater the number of bits moved per cycle, the faster the computer.

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C

• CAD—Computer-aided design. CAM—Computer-aided manufacture.
• CAR—Computer-aided retrieval.
• CD — Compact disc.
• CD-I — Compact disc–interactive.
• CD-ROM — Compact disc–read–only memory.
• CD-V — Compact disc–video.
• CLUT— look-up table.
• CMYK—Cyan, magenta, yellow, and black.
• CODEC — Coder/decoder.
• CPU—Central processing unit.
• CRT—Cathode-ray tube.
• Cache — In computers, a section of reserved memory designed to allow the central processing unit (CPU) to process data faster. Cache can also be used to speed video and Internet access.
• Card—In the Macintosh and Amiga world, cards are analogous to boards.
• CCD array—An electronic imaging device that uses many charge-coupled devices (CCDs) to convert a large amount of image information to digital values at the same instant.
• CCD scanner—An optical scanner that uses a linear CCD array to capture a row of pixels simultaneously. The array is then moved laterally to scan the image.
• Central Processing Unit (CPU)—The brain of the computer that performs all calculations and routes data via a bus to and from other computer components.
• Channel—In electronic imaging, the holding of colour information in a separate location. Each component of the colour data, RGB, is held in a separate channel. In other colour modes, four channels are used to hold the CMYK data. Channels can be likened to separation negatives or to printing plates.
• Charge-Coupled Device (CCD)—An array of photo sensors that detect and read out light as an electronic signal.
• Clone — In electronic imaging, the function by which an exact duplicate of an image or part of an image is made.
• Code — The vernacular for any machine or higher-level language instructions.
• Colour Graphics Adapter (CGA)—In computers, the original standard for colours display on the personal computer. CGA was limited to a spatial resolution of 320 􏰃 200 pixels and 4 colours from a palette of 16 colours. In text mode, characters are formed from an 8 􏰃 8 matrix at a resolution of 640 􏰃 200. Today many monitors are capable of displaying more than 1000 pixels and millions of colours.
• colour Look-Up Table (CLUT)—CLUTs provide an algorithm that will allow for the translation of RGB colour into some other colour space, such as CMYK. If an area of the image that is displayed as red comprises 85 percent red, 10 percent green, and 10 percent blue, then a CLUT would be written to translate the RGB data into 5 percent cyan, 60 percent magenta, 35 percent yellow and 0 percent black. The CLUT exists as a predetermined set of values in tabular form, thus making it unnecessary to calculate the appropriate values for each change in display colour.
• Compact flash — Flash memory is removable memory that does not a need power supply to maintain the information stored on the chip. Additionally, flash memory delivers faster access times and better shock resistance than hard disks. This media was invented in Japan in 1984, by Dr Fujio Masuoka of Toshiba.
• CMOS (complimentary metal oxide semiconductor) chip — Another technology used in chips. In the active pixel CMOS method, the electrical power design has been modified to use power more effectively by linking pixels together to lower power requirements. CMOS chips are not capable of higher resolutions than CCD simply are more efficient. To find CMOS technology more integrated into digital cameras will require industry to reinvent manufacturing.
• colour mapping—colour mapping uses a colour look-up table (CLUT) for monitor display purposes.
• Compact Disc-Interactive (CD-I)—A new standard for the use of CDs containing still images, moving image sequences, and audio tracks. A CD-I device will allow a user to interact with the program contained on the disc. It requires a CD- I player and appropriate monitor. The CD-I player has its own microprocessor and represents a higher level of built-in intelligence than a standard CD or CD-ROM player.
• Compact Disc Read-Only Memory (CD-ROM)—Discs that can hold text, images, and sound and are a major means of data storage and distribution. Their storage capacity is in the region of 650MB (megabytes) of data. Since the throughput of CD-ROM players is standardised at 150KB (kilobytes) per second, these devices are capable of playing audio CDs.
• Compiler — A software type program that converts high-level programming language into machine language in preparation for execution. Compiled languages run faster than interpreter languages and can be compiled into executable programs.
• Compression — In electronic imaging, image data are compressed to achieve smaller files for storage and/or transmission. LZW and Huffman codes are two compression algorithms widely used on images. Video is often compressed using an interframe process in which redundancy shared by two frames is ignored. In transmission of image data under this scheme only the differences between the frames are transmitted, thus decreasing the time necessary to transmit the data.
• Computer-Aided Design (CAD)—The use of computers to assist in design activities such as graphics, architecture, engineering, and page layout.
• Computer-Aided Manufacturing (CAM) —The use of computers to assist in the design and monitoring of a manufacturing process.
• Computer-Assisted Instruction (CAI) —The use of computers in the classroom to advance teaching and learning. Almost any involvement of computers in providing instruction, questioning, or feedback in the teaching-learning paradigm has been labeled CAI. Currently, CAI has come to mean the use of a computer in the control of multimedia for the purposes of instruction.
• Crash—In computers, a slang term meaning to bring the computer to a nonfunctional state. Typically, the computer is unable to recognise any event and it cannot respond in any way. The usual way out of this stalemate situation is to reboot the computer.
• CT merge—In electronic imaging, the function of combining the files of two continuous-tone images to provide a smooth transition between the images.
• Cursor—A symbol, such as a cross, a blinking line, or a block, that locates on the monitor the insertion point where an action, such as cutting and pasting or input, is to begin or conclude.
• Cut-and-paste — A computer operation that is analogous to a scissors-and-glue operation with paper used on an image or text. More sophisticated programs are beginning to replace cut-and-paste with select-and-drag operations that perform the same function but more quickly and visibly.

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D

• DA — Digital-to-analog.
• DAC — Digital-to-analog converter. DAD — Digital audio disc.
• DAT—Digital audio tape.
• DOS—Disk operating system.
• DPI—Dots Per Inch. Similar to PPI or point/pixels per inch.
• DRAM—Dynamic random access memory.
• DRAW—Direct read after write.
• DSP—Digital signal processing.
• DSU—Digital storage unit.
• DTP—Desktop publishing.
• Database—In computers, the holding of information in an electronic form in a cross-referenced structured format that allows for rapid retrieval and cross-referring. Large databases are used for a variety of data-intensive fields. Some multimedia applications use databases as the referencing tools to rapidly access and display visual data.
• Deblurring — In computers, when an image is blurred from either linear motion in a specific direction or from a lack of depth of field, the image sharpness may be restored by deblurring techniques such as the use of a Wiener filter.
• Decoder — A device that takes in composite video and decodes the signal information into separate signals for picture (RGB), sync, and timing. Decoders may be used to input video into a computer when sync signals are weak or when picture signals need boosting in a particular channel.
• Degauss — (1) To demagnetise. When done deliberately in a degausser, this means applying first a strong ac magnetic field that can reverse the state of all magnetic domains in the object being demagnetized, and then decreasing the field strength in an orderly way to zero. This process leaves the state of the various magnetic domains utterly random and thus demagnetised. (2) In computers, the act of demag- netizing the cathode-ray tube (CRT) in the monitor. The use of the CRT builds up a charge on the surface of the monitor. Degaussing the monitor prolongs monitor life and minimises distortion.
• Desktop pictures — A digital photograph that is displayed as a background on many home and office computers. Desktop pictures can either be supplied as a part of the system’s operating system or imported from personal collections, which is more common.
• Desktop publishing — In graphic arts reproduction, a compact publishing system that includes a personal computer, word processor, plate makeup, illustration and other software, PostScript page description language, and image setter to produce halftone films.
• Digital halftone — A halftone produced on a digital device such as a laser printer. Typically the dot size is fixed by the resolution of the printer (300dpi). The digital half-toning creates the effect of variable size by the process of dithering. The dithering process creates a cluster of two or more dots and varies the percentage of black dots to achieve a grey tone. A typical 300dpi laser printer can produce a dithered cluster of 4 􏰃 4 cells and achieve a halftone resolution of 75dpi. However, the number of grey levels is a product of the cluster. In this example, the number of grey tones is 16 (4 􏰃 4). If the number of required tones is increased, then the resolution (dpi) decreases.
• Digital image—An image that is represented by discrete numerical values organized in a two-dimensional array. The conversion of images into a digital form is known as digital imaging. Hence, manipulation of the image in digital form is called digital editing, retouching, enhancement, etc.
• Digital plates—Printing plates made directly from digital data.
• Digital printing—Printing from digitally produced printing plates.
• Digital-to-Analog Converter (DAC)—In computers, a component that converts digital data to analog information. Many cathode-ray tubes (CRTs) are analog-driven devices. For the computer to display the image, the data must be changed from the digital domain to voltage in the analog world. Many A/D boards are also D/A boards. Targa boards, among other capture/display boards, contain both an A/D circuit and a D/A circuit.
• Digital video—The images displayed by the monitor are digital representations held by and displayed through the computer. Such an approach to video gives opportunity to the manufacturing of intelligent television at high-definition levels.
• digitiser — The device that converts analog data into digital data. The analog data are sampled and quantized. The number of bits that the digitiser is capable of quantising determines the number of grey levels captured by the digi- tizer. An 8-bit digitiser can digitise 256 levels of brightness.
• Disk — Generically, the platter of magnetically coated mate- rial that stores data for the computer. These disks are inter- changeable among computers of similar type. Software exists that allows for the reading of disks across platforms. Data are recorded serially in concentric circles called tracks. Disks come in several sizes and density capacities. Originally, the flexible, or floppy, disk was 8 inches in diameter and held more than 360 kilobytes of data on a single side. This was followed by a floppy disk that was 3.5 inches in diameter, double-sided, high-density, with a capacity of 1.44 megabytes of data. [Disks have evolved significantly from those small capacities of 650MB with compact disks (CDs) or digital video disks (DVDs). Dual-layer recording allows DVD􏰁R and DVD􏰀R discs to store significantly more data, up to 8.5GB (gigabytes) per disc, compared with 4. 7GB for single-layer discs].
• Disk Operating System (DOS) — Personal computing was diskette-based and required system software —the instructions to the computer on what to do and how to operate stored in a form accessible to the computer. Early computers usually lacked hard drives, so a floppy diskette called the operating system diskette was used to store data, programs, and the computer operating system. Current usage has limited the term DOS to describing “antique” operating systems of IBM-type platforms that now use Microsoft’s Windows operating systems.
• Display monitor—The common monitor in an electronic imaging system is a device for displaying images and is a cathode ray tube (CRT). Another is Liquid Crystal Display (LCD), which is coated with bands of phosphors that produce red, green, and blue colours. The calibration and brightness of this device is a significant variable in the electronic imaging world.
• Dithering — In electronic imaging, the variation in the number of ink dots to represent a tone of grey. Dithering requires that a physical area with a known matrix of dots called a cell be established. For example, a cell may contain an 8 􏰃 8 matrix. If all 64 locations are filled with ink dots, then the area appears black; if all 64 locations contain nothing, then the area appears white. Varying the number of filled and unfilled cells can give the perception of a grey tone. Electronically adjacent pixels are turned on or off or are assigned different colours, thus creating the appearance of a tone of grey or another shade or colour.
• Dye sublimation — Refers to a process in which a pixel-for- pixel image is written to a hard copy output device. This type of printing is referred to as a continuous tone image and is considered to exhibit the highest degree of data or similarity to photographic paper. Receiver materials are exposed to cyan, yellow, and magenta dyes and transferred by heat to the receiver material. This type of print is capable of rendering 300 dots per inch and is the most expensive type of digital printer.
• Dynamic range—Scenes and subjects contain a range of brightness or reflectance. The difference between the region of highest brightness as compared to the region of least brightness describes a scene brightness range, or dynamic range. CCDs record data more effectively when using a narrow brightness range similar to colour slide films. High brightness ranges create problems for chip response.
• Dynamic Random-Access Memory (DRAM) — The memory component of the computer. These chips hold data and instructions supplied by the software program in a quickly accessible state, thus reducing the need for the computer’s central processing unit (CPU) to continually access the program disk. These chips hold data as long as there is power. Once the power is turned off the DRAM loses its contents.

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E

• Edge detection — In electronic imaging, a convolution technique designed to determine local contrast (grey-level) differences across some measure of homogeneity. The zone of change between two different regions is processed by an operator so that the zone itself is obvious.
• Electronic photography — Electronic photography was a term that was first used to describe digital and represented the electronic recording of optical images in analog or digital form. Image capture used photo-multiplier devices or linear or area CCDs with the recording on magnetic, optical, or solid-state media. Images were made with a dedicated digital camera or video camera and converted from silver halide originals into electronic form. The combining of silver halide and electronic technology was also known as hybrid technology.
• Electronic publishing—The production of printed material making use of a computer with an appropriate software program, which typically accommodates text and illustrations with layout control and a peripheral printer.
• Encoder — A device that takes an RGB picture signal and timing signals and composites these data into composite video.
• Enhanced Graphic Adapters (EGA)—In computers, this cathode ray tube (CRT) superseded the colour graphics adapter (CGA) and provided higher resolution and more colour. Typically EGA could provide resolution of 640 􏰃 350 and 16 colours from a palette of 64 colours. In text mode (one of twelve modes), characters are formed from an 8 􏰃 14 matrix, thus giving higher text resolution.
• Extended memory — A de facto requirement in the processing of images or the use of multimedia on DOS-based plat- forms. Extended memory occurs above 1 megabyte. Four to eight megabytes has become standard RAM in multimedia machines.

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F

• Fax— Facsimile.
• File — (1) In computers, the file is the basic structure for saving or storing data. Images, spreadsheets, and text documents are stored as files to be retrieved later by the programs (applications) that created or can operate on the file. (2) In electronic imaging, the digital database that represents a picture or a line image, or a set of instructions.
• Fire wire—A cross-platform, high-speed, serial data bus defined by the IEEE 1394–1995, IEEE 1394a-2000, and IEEE 1394b standards capable of moving large amounts of data between computers and peripheral devices. FireWire features simplified cabling, hot swapping, and transfer speeds of up to 800 megabits per second (on machines that support 1394b).
• Firmware — In computers, an instruction set or program that is stored and retrieved from programmable ROM or plug-in modules that are self-initiating and do not typically require software. Firmware differs from software in that the application exist as a program on a floppy disk or in a hard drive, while firmware is built into a chip or PROM.

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G

• Gigabyte—One billion bytes, or 1024 megabytes.
• GUI — Graphical user interface.
• Hard copy—(1) A computer-screen image printed out on paper or film. (2) A photographic print from a microfilm or other image projection, as distinct from an image projected only for visual inspection.
• Hard disk—A magnetic storage device that is capable of holding thousands of megabytes, in contrast to floppy disks that hold approximately 3MB. Hard disks are also referred to as fixed disks. These disks contain a platter that is spun at a high speed and a read/write head that accesses data. The hard disk maintains its integrity (data) when the power is off. Density of these disks is measured in hundreds of millions of bytes.

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H

• HD — High density.
• HDTV—High-definition television.
• Histogram — In computers, a description of a continuous- tone image through the tabulation of the number of pixels for each grey level extant. The tabulation is displayed as a bar graph or histogram with the vertical axis as the number of pixels and the horizontal axis being the number of grey levels.
• Home—In some computer applications, home is used as a synonym for the main menu. Home is the starting place from which to launch sub-applications from the main program. In HyperCard, a relational database, home is the launching pad for stacks.

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I

• Icon — A primary graphical object in a graphical user inter- face. The icon may represent a device such as a drive or scanner. It may also represent a file, message, or application. Icons may change their appearance when an event occurs. An open file may be represented by a differently appearing icon than when the same file is unopened.
• Image processing—The alteration, enhancement, and analysis of images for the purpose of improving the pictorial representation or extracting data from the image. Image processing relies on a number of well-tried algorithms that simplify and speed the process. While image processing is applicable to optical and analog approaches, the term’s use is mostly limited to digital imagery.
• Indexed colour—In electronic imaging, a look-up table containing colour information that facilitates displaying 24-bit colour on an 8-bit driven monitor including only 256 distinct colours.
• Initialize—In computers, starting a component for the first time, such as initialising a video board. To write to a disk, the disk must be initialized (formatted) so that it is prepared to receive data. This initialisation organises the sectors and tracks appropriately.
• Ink-jet printer—A computer-controlled output device that sprays ink through very fine nozzles. The fineness of the nozzle determines the dot size of the ink spray. Usually, the water-based ink will be sprayed in liquid form or it may be heated and sprayed as a tiny bubble. Ink-jet printers can resolve between 150dpi to 360dpi. Many ink-jet printers will offer printer resolutions in different units such as 720, 1440, or 2880dpi. Black-and-white and colour output are both possible with ink-jet printing.
• Input/Output (I/O)—A device that allows data to be entered into the computer (mouse, graphics tablet) or a device that accepts data for review (monitor, printer). I/O may also refer to the controller of these devices. I/O compatibility is a major consideration in the fabrication of an imaging or graphics computer workstation.
• Input scanner—Any device that can capture an electronic representation of reflection or transmission of original material and convert it into a digital representation of the original.
• Interactive—Communication between the computer and the user. There are several levels of interactivity. The highest level occurs in a time span that is real-time or near real- time.
• Interlace — The scanning method of displaying images on the cathode-ray tube (CRT) whereby each of two fields is displayed every 60th of a second. The “a” field is composed of every odd line and the “b” field is composed of every even line. The two are interlaced together to represent one frame. Interpolation—A method of modifying the image size. Digital systems are capable of recording a fixed number of pixels. Sometimes there may not be enough pixels for a particular application or there may be too many and soft- ware may be called on to change the number of pixels. This type of image processing is defined as interpolation. JPEG—Joint Photo Experts Group.

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K

• kb — Kilobit.
• kB — Kilobyte.
• Kernel—A targeted group of pixels in a closely defined array that can be convolved, or evaluated with weighted coefficients. The value of each pixel in the kernel is dependent upon its neighbours. The array of weighted coefficients is called a mask. The size of the mask is the same as the kernel. In many texts the terms kernel and mask have become interchangeable.
• Kerning—The adjustment of the space between type characters to improve their visual appeal. Certain page layout programs, including QuarkXPress, and languages such as PostScript allow desktop publishing to adjust spacing.
• Keying — Keying is the act of combining pictures from one signal source into a picture sourced from a different signal. Keying can be controlled by frames or by colour, such as chromakeying.

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L

• LCD — Liquid crystal display.
• LED — Light-emitting diode.
• Library — In computer parlance the library is a repository of a file from which the software may make calls. The calling of subroutines or procedures from the library can speed soft- ware development and provide for standardised approaches to the writing of code.
• Linear array—Is another method of pixel organisation in a CCD. In this approach, a single row of pixels is located in only the vertical orientations (the y matrix). A finite number of pixels will exist in this direction dictated by the manufacturing of the CCD just as in the area array device. The number of vertical pixels is fixed and the array is moved across the field using a small motor.
• Linear output—Output that varies proportionally to the input. Video displays are linear with respect to the accuracy of the tone reproduction.
• Liquid Crystal Display Projector — Liquid crystal display (LCD) technology was developed in 1973 and was most commonly used in digital watches and handheld calculators, where its light weight, low power, and high resolution made it the ideal presentation medium. Liquid display material is activated electrically and is now also used to form images for laptop computers and word processors. These items use a duty-type LCD, where the individual pixels are controlled by a liquid crystal matrix. These duty-type LCDs can be used to display colour and video images, but they have slow response times that make them impractical for rapidly changing images. On the other hand, active matrix LCDs have a transistor at each pixel point that controls only that pixel and can respond much more rapidly to image changes. This new generation of active matrix LCDs is competitive with conventional CRT displays (TV monitors). Because these new LCDs provide a quick change-response time, high resolution, impressive picture quality, and excellent colour reproduction, they are being used for the video market and high-speed computer displays. LCDs consume very little power and are extremely lightweight compared with conventional CRT displays, making them ideal for use as very large, flat-screen, wall-mounted video image displays. This technology also provides for convergence-free colour video projection systems.
• Load — The transfer of data or the application from storage (hard or floppy disk) to the memory (RAM) of the computer. Lock-up—A glitch that prevents a computer from accepting instructions from an input device. In effect, the user is locked out and the keyboard is locked up. In MS-DOS systems, holding down the control, alternate, and delete keys at the same time will undo a lock-up by warm-booting the system. Other computers require a different sequence of keys to escape from a lock-up.
• Logic board — The primary circuit board in a computer that holds the CPU, ALU, RAM, ROM, and the bus network for the various peripherals.
• Look-Up Table (LUT)—An image-processing operation that accepts input and maps it via a table based on some point- processing algorithm to specific output. The conversion of RGB to CMYK (input to output) relies heavily on a colour look-up table (CLUT).

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M

• Machine code — The binary language that the computer understands and into which higher-level languages are translated.
• Mapping—In electronic imaging, the process of transforming input brightness to output brightness.
• Mb — Megabit.
• MB — Megabyte.
• MBPS—Megabytes per second/megabits per second. Megabyte (MB) — Loosely, one million bytes. More precisely, 1,048,576 (220) bytes.
• Memory—The active memory, or core memory, of the computer in which all data and instruction reside before and during processing. Data in memory is existent only as long as the system is operating. Once powered down, the memory becomes empty.
• Memory card — Digital image files are stored on this tempo- rary location in digital cameras. The memory card is capable of reading and writing both while in the camera or in a card reader inserted to the CPU. Different names have been given by each company to its memory card, such as Smart- Media, Memory Stick, Compact Flash, SD, and xD Media.
• Microcomputer—A computer whose basic operating capabilities are on one chip. Using CISC technology, microcomputers are compact and powerful. The microcomputer has become known as a personal computer (PC).
• Minicomputer — A mid-size computer having processing power close to that of a mainframe, but at a lower price while surrendering some of the mainframe’s key attributes, for example, supporting fewer terminals. Minicomputers have evolved into workstations optimised for specific applications. As processing power, RAM size, CPU speed, and bus speed/width increase for minicomputers and for microcomputers, the distinction among the three levels of computers is difficult to characterise.
• Motherboard — In computers, the same as a logic board. In Microsoft MS-DOS systems the motherboard holds all the processing chips and circuitry necessary for the computer to function. The circuitry of the motherboard integrates all the bus slots, hard drives, display boards, and their controllers.
• Mouse — In computers, a hand-held input device that controls the cursor when moved about. The mouse has become the most popular pointing device for graphic user interface environments.
• MPEG—Motion Picture Experts Group.

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N

• Network—In computers, a group of connected computers sharing a common protocol for communications. These networks can be local or wide in area and can connect from several to many thousands of terminals.
• NTSC—National Television Standards Committee.
• Nubus — A special high-speed bus found in Macintosh II computers. The Nubus is distinguished from other bus designs by its protocol for moving data within the computer. [It was very helpful with 8-bit work in the 1990s but is no longer widely used].
• Nyquist theorem — A mathematical way of determining when a sample composed of high frequency will be imaged and displayed without degradation. The theorem states condi- tions under which the samples can be used to reconstruct the original signal with maximum fidelity. The Nyquist criterion states that the subject must be sample-limited and that the sampling frequency must be at least twice the signal bandwidth of the system.

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O

• OCR — Optical character reader/recognition.
• On line — (1) In monitoring a process, an almost immediate analysis of the data collected, thus reducing the time lag between the discovery of an error and the correction of the process. (2) In computers, the term simply means that the computer is functioning. Sometimes on line is used to mean that the computer terminal is in communication with a host computer operating system.
• Optimise—In computers, the optimisation of the hard drive causes contiguous sectors on the block to be available for storage, thus achieving faster reads and writes to and from the hard drive.
• OS—Operating system.

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P

• Paint — A term that describes the changing of pixel data. In image processing there are two fundamental actions, selection tools and paint tools. Paint tools change pixels that were selected in some way, such as by brightness.
• Peripherals — In computers, attachments that are connected through a variety of data input/output channels, such as printers, scanners, and plotters.
• Pixel—Picture element, the smallest component of a picture that can be individually processed in an electronic imaging system.
• Pixel cloning—In electronic imaging, copying a pixel or group of pixels from an area of an image for the purpose of adding them to another area—for example, to remove unwanted detail.
• Pixelation — When the spatial resolution of an electronic, computerised image is low, the individual pixels or groups of pixels become visible. This blockiness is known as pixelation. The degree of visibility of these blocky pixels depends upon the viewing distance from the cathode-ray tube (CRT).
• Plasma display—In computers, cathode-ray tubes (CRTs) are only one form of display technology. As computers become smaller and more portable, the display is a limiting factor in achieving even smaller computers. Plasma displays are flat-screen displays in which a wire mesh sits sandwiched between two sheets of glass in an environment of inert gas. Each crosspoint of the mesh represents a pixel that can be addressed by the computer.
• Plumbicon—In electronic imaging, video tube–type cameras use various types of pickup tubes to image a subject. The plumbicon tube is particularly noted for its ability to image under low lighting conditions. It has been used widely in the area of video surveillance.
• Pointing device—In computers, the graphic user inter- face (GUI) functions most efficiently through the use of a pointing device that locates functions, addresses menus, or launches events.
• Point processing—In electronic imaging, a point process such as a histogram equalisation is used to correct the brightness levels in an image in order to achieve a contrast change.
• PPS—Pictures per second. Pseudo-colouring — In electronic long as the computer is on line, data will remain in RAM. Once the computer is turned off, all data in the computer will be erased.

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R

• Raster—In electronic imaging, the scanning pattern of the electron gun across and down the cathode-ray tube (CRT) as it paints or refreshes the image. In computer graphics, a rectangular matrix of pixels such as a bitmap image.
• Raster graphics — In computers, screen graphics are displayed by the cathode-ray tube (CRT) according to a raster pattern that is controlled by the deflection circuit of the electron gun and the circuit of the metal grid inside the picture tube. Graphic characters are created according to which pixels are excited by the electrons. Characters are composed of groups of pixels. The main drawback to raster-drawn graphics is the jagged appearance of text.
• Raster image processor—In electronic imaging, used to convert vector images to raster images in computers that use both kinds of image files.
• Raster unit—In electronic imaging, the distance between the midpoints of two adjacent pixels.
• Resolution—In electronic imaging, the number of horizontal and vertical pixels that comprise the image. The minimum resolution acceptable for scientific image processing is 512 􏰃 512 pixels. If the term is used to describe brightness levels (contrast resolution), then the minimum levels of brightness are 256.
• RGB—Red, green, blue (video).
• RIFF—Raster image file format.
• RIP—Raster image processor.
• ROM—Read-only memory.
• RUN—In computers, the instruction to begin execution of a programmed task.
• Run-time error—In computers, a program error other than syntax that causes the computer to crash. The error is not identified during compiling and manifests itself only at the time the program runs.

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S

• Scaling—(1) The process of comparing the dimensions of a photograph or other image that is to be reproduced to the dimensions of the space allotted to the reproduction, including determining whether cropping will be required because of a difference in the height-to-width proportions of the original and the reproduced images. One method is to make a rectangular outline the same size as the original on paper, draw a straight line through two opposite corners, and add lines corresponding to the dimensions of the space available for the reproduction. (2) In photomechanical reproduction, determining the correct dimensions of an image to be reduced or enlarged to fit an area. (3) In electronic imaging, images are resized by percentage, where 100 percent is the original input image.
• Scanner — (1) A scanner is a device that can translate a transmitted or reflected light image into a digital form. Scanners include rotary drum scanners, flatbed scanners, handheld scanners, and dedicated film scanners. (2) In electronic imaging, a peripheral device that allows for the conversion of flat art, photographic prints, and transparencies into digital data that can be accessed by photographic imaging software.
• Scratch disk—In electronic imaging, many image manipulation programs require that a copy of the image being processed be held in storage so that operator errors can be undone. Because of the size of images, the copy image is usually held in a reserved area of the hard disk called a scratch disk. After the image manipulation is complete, the copy image is removed from the hard disk and that area is no longer reserved.
• Screen display—Viewing electronic images on a screen is referred to as soft viewing or proofing. This is because there is no hard copy image as of yet. Images viewing this way contain 72 dots per inch.
• Separations — In electronic imaging, the creation of four separate files, one for each of the four process colours: cyan, magenta, yellow, and black. The software for separations may be machine-specific or may have various look-up tables to maximise colour appearance for specific output devices.
• Serial port — In computing, one of the oldest two standard input/output communications ports used by the computer to control external peripherals such as a modem. Serial ports send data one bit at a time in a sequential string. It is a slower transfer than a parallel process.
• Slow scan—In electronic imaging, the transmitting of video signals at a rate slower than real time is called slow scan. This is generally done because of bandwidth limitations. Slow scan video can be sent over radio frequencies other than those allocated for broadcast and over standard tele- phone lines.
• Small Computer Systems Interface (SCSI)—In computers, there are several means of accessing peripherals through a port that conforms to a particular protocol for data transfer. SCSI is one protocol that has become a de facto standard for data input/output in the Macintosh platform. Scanners and film recorders connected to a Macintosh exclusively use SCSI. Other peripherals such as removable cartridges and optical drives also employ SCSI.
• Smoothing filter—In electronic imaging, an electronic filter used to reduce the cross-hatch noise pattern that can appear with the use of charge-coupled devices.
• SRAM—Static random access memory.
• Static memory—The retention of information in semiconductor memory without refreshing or recirculating.
• Still video—An electronic method of recording individual images using 2-inch floppy disks that hold either 50 field images or 25 frame images.

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T

• Terabyte—One trillion bytes (TB)
• Tiff—In electronic imaging, images that are captured and saved to a storage medium as a file and are described according to some algorithm. The description is usually written prior to the image data in an area of the file called the header. Tagged image file format, or TIFF, is one such header description widely used by electronic imaging programs. Others include TGA, VST, PCX, PICT, and PIC (to name only a few). The proliferation of a multitude of image headers has caused serious porting problems. Many image-manipulation software programs only read a limited number of header files. A number of commercial conversion programs allow for the translation of one file format into another.
• Trackball — In computers, a graphic user interface device that controls the cursor when rotated. The trackball can be rotated 360 degrees in its cradle, causing the cursor to move to any position on the screen. Buttons on the cradle operate in the same fashion as buttons on a mouse.
• True colour—In electronic imaging, the use of 16,777,216 colours for display description purposes. This standard is a 24-bit display system: 8 bits for the red channel, 8 bits for the green channel, and 8 bits for the blue channel. True colour is the equivalent of photographic quality.

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U

• Undersampling—In electronic imaging, the sampling of an analog signal at less than the Nyquist theorem.
• Underscanning — In electronic imaging, the displaying of a raster image so that the scanning raster is visible. Under- scanning, although infrequently used, ensures that image data are not hidden.
• Unsharp masking filter—In electronic imaging, the digital counterpart of photographic unsharp masking. This digital equivalent uses a neighbourhood process to subtract an unsharp (smooth) image from the original image.
• USB — Universal Serial Bus (USB) is a connectivity specification and provides ease of use, expandability, and speed for the end user. USB is arguably the most successful interconnect in computing history and was co-released in 1995 at 12 Mbps by Intel, USB today operates at 480 Mbps and can be found in over 2 billion PC, CE, and mobile devices.

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V

• VBI — Vertical blanking interval.
• VCNA—Video colour negative analyzer.
• VCR — Videocassette recorder.
• VDT — Video display terminal; visual display terminal.
• VDU — Video display unit; visual display unit.
• VFS—Video floppy system.
• VGA—Video graphics array.
• VHF — Very high frequency.
• VHS—Video Home System (trade name).
• VHS-C — VHS-Compact.
• VTR—Videotape recorder.
• Vector graphics—In electronic imaging, graphics that are displayed on the cathode-ray tube (CRT) as represented by a mathematical description. This mathematical description causes the CRT to scan the pattern as described and not according to a raster pattern. The result is a very high- quality graphic without jagged edges. Vector graphics are displayed slowly because of the mathematical description and would be evidenced in Microsoft PowerPoint, for example.
• Video Random-Access Memory (VRAM)—In computers, a specialised form of RAM that can simultaneously write data to the display monitor as it is receiving data from the central processing unit (CPU). This form of dual-port chip greatly speeds up the displaying of images on the cathode- ray tube (CRT).
• Virus—A computer program designed to disorient, slow down, or destroy the computer’s operating system or data files or the hard disk’s directory.
• WB—White balance.

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W

• Window—(1) In computers, a frame or frames in the cathode- ray tube (CRT) that display different processing operations. For example, one window may display a spreadsheet while a second window on the same CRT displays a word processing document. Window environments are a form of graphic user interface (GUI). (2) In computers, a proprietary graphic user interface (GUI) operating system for IBM and compatible platforms by the Microsoft Corporation.
• Word processing—In computers, a software program that allows the user to enter text for the purpose of writing a document. The text may be edited and sent to a printer for hard copy.
• Write—In computers, to store data on a floppy disk, hard disk, or optical disk.
• Write Once Read Many (WORM)—In computers, a storage device that is written to by a laser. This system allows for a large amount of data to be stored. Optically based, this approach can only write once to a given sector on the optical platter. However, the data can be read from the platter as often as necessary.
• Write-protected—In computers, hard and floppy disks can be physically and virtually manipulated to prevent writing over important data that exist on the disk. Writing over data has the same effect as erasing data.

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Y

• YIQ—In video, NTSC standards abbreviate chrominance as I and Q, and abbreviate luminance as Y. I and Q refer to hue and saturation. Y refers to value or brightness.

date modified - 23.04.2020 14:03