Glossary
- A digital image that can include as many as 256 possible colors. In this kind of image, 8 bits are allocated for the storage of each pixel, allowing 2 to the power of 8 (or 256) colors to be represented.
- A digital image that can include approximately 16 million possible colors. In this kind of image, 24 bits are allocated for the storage of each pixel, allowing 2 to the power of 24 (or more than 16 million) colors to be represented.
- Index terms used to search a database.
- Image-specific set of colors chosen to most closely represent those in the original source. Part of a custom color look-up table.
- A rule (often mathematical) governing computer processes.
- Information (such as arrows, pointers, words) added to an image. Annotations to a digital image might be stored in layers separate from the image.
- An image meant to have lasting utility. An "archival" digital image is generally an image kept off-line in a safe place; it is often of higher quality than the digital image delivered to the user.
- AAT. One of the structured vocabularies offered by the Getty Art History Information Program (AHIP), the AAT, begun in 1980, is a hierarchical arrangement of more than 90,000 terms in art and architecture. Published in print and electronic forms by Oxford University Press.
- AITF. A three-year project jointly sponsored by the Getty Art History Information Program (AHIP) and the College Art Association (CAA) which reached agreement on the categories used to describe works of art. Final results are summarized in Categories for the Description of Works of Art.
- Visual effects introduced into a digital image in the course of scanning or compression that do not correspond to the image scanned.
- Indexing of a text done by computer without human intervention (usually by finding the words occurring most frequently within the document).
- The transmission capacity of a communications channel, usually expressed in bits or bytes per second (the former is also called baud rate).
- An image created from a series of bits and bytes that form pixels. Each pixel can vary in color or gray-scale value. Also known as a raster image.
- Automatically locating the correct edge of an image on a scan so that marking from the edge, frame, etc. is not captured.
- A small image (usually derived from a larger one). Browse images (often called "thumbnails") permit a user to view a dozen or more images on a single screen.
- Temporary storage space within a computer system.
- see Scanner
- The report of the Art Information Task Force, which defined information about works of art from a researcher's perspective.
- Charge-coupled device array. Light-sensitive diodes used in scanners and electronic cameras. These usually sweep across an image and, when exposed to light, generate a series of digital signals that are converted into pixel values.
- The standards adopted by the International Telecommunications Union (ITU), formerly the Comiteacute; consultatif internationale de teacute;leacute;graphique et teacute;leacute;phonique (CCITT), to compress page images. All fax machines in common use employ one or both of these standards.
- 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 550 megabytes of data.
- Positioning an image properly within the digital field of vision so that it is framed appropriately.
- A systems architecture design that divides functions (which might be part of a single application) between two or more computers. The client is the machine that requests information; the server is the machine that supplies it. A typical client/server architecture for imaging might allow a server to store and transmit a compressed file, and the client to decompress, process, and display the image.
- Computer Graphics Metafile. An image file format designed to handle a wide range of image types, but currently used primarily for vector graphics.
- Cyan Magenta Yellow Black. A system for reproducing color in print, which creates the color spectrum using cyan, magenta, yellow, and black. Used in four-color printing.
- The process of altering colors as they appear in a digital image or in print to ensure they accurately represent the work depicted.
- see Dynamic range
- see Palette
- Systems that attempt to produce consistency in the representation of color in image files, across image capture, display, and output devices.
- A means of representing the spectrum.
- Compression is the process of squeezing more data into a smaller storage space. Decompression is the retrieval of compressed data and its reassembly to resemble its original form (before compression). see also Lossless compression, Lossy compression
- A type of image-capture device that sits on a copystand and can be raised or lowered to get closer to or farther from the material to be scanned. Involves a physical set-up similar to microfilming, or copy photography.
- see Compression
- An image that is created from another image, usually by eliminating part of it. Common techniques used to create a derived image include taking a detail, subsampling to a lower resolution, using lossy compression, or using image-processing techniques to alter an image. Also called derivative image.
- A camera that directly captures a digital image without the use of film.
- A digital "container" that surrounds an image with information (or metadata). Such information might be used to find the image, guarantee its authenticity, or limit access to authorized users.
- see Watermark
- An image composed of bits and bytes. see Bit-mapped image or Vector graphic.
- To convert an image into binary code. Visual images are digitized by scanning them and assigning a binary code to the resulting vector graphic or bit-mapped image data.
- Light-sensitive electronic components used in image capture. They function as one-way valves that sense the presence or absence of light and create a digital signal that the computer converts into pixel values.
- Textual information that describes a work of art or image, recording its physical characteristics and placing it in context.
- The transfer of information from one computer to another. Frequently used to describe file transfer from a network file server to a personal computer.
- Dots per inch. A measurement of the scanning resolution of an image or the quality of an output device. Expresses the number of dots a printer can print per inch, or monitor can display, both horizontally and vertically. A 600-dpi printer can print 360,000 (600 3 600) dots on one square inch of paper.
- 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.
- The color depth (or possible pixel values) for a digital image. The number of possible colors or shades of gray that can be included in a particular image. 8-bit images can represent as many as 256 colors; 24-bit images can represent approximately 16 million colors.
- Encapsulated PostScript. An image-storage format that extends the PostScript page-description language to include images.
- An image-capture device resembling a photocopy machine. The object to be scanned is placed face-down on a glass plate. The CCD array passes beneath the glass.
- File transfer protocol. A method of moving or transferring files between computers on the Internet.
- See Video digitizer.
- A digital image that covers the entire screen of a workstation.
- Graphic Image File format. A widely supported image-storage format promoted by CompuServe that gained early widespread use on on-line services and the Internet.
- The range of shades of gray in an image. The gray scales of scanners and terminals are determined by the number of grays, or steps between black and white, that they can recognize and reproduce.see also Dynamic Range
- Technical information packaged with an image file, which may be of use in displaying the image (e.g., length and width in pixels), identifying the image (e.g., name or source), or identifying the owner.
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- HTML. An encoding format for identifying and linking electronic documents used to deliver information on the World Wide Web.
- A system of letters and numbers used to classify the iconography of works of art, developed in the Netherlands.
- Employing a device (such as a scanner) to create a digital representation of an image. This digital representation can then be stored and manipulated on a computer.
- Making digital changes to an image using image processing.
- The alteration or manipulation of images that have been scanned or captured by a digital recording device. Can be used to modify or improve the image by changing its size, color, contrast, and brightness, or to compare and analyze images for characteristics that the human eye could not perceive unaided. This ability to perceive minute variations in color, shape, and relationship has opened up many applications for image processing.
- File storage format used with Kodak's PhotoCD.
- An international compression standard designed for images with very little color or gray scale (such as document page images).
- JPEG File Format. File storage format for images compressed with the JPEG algorithm.
- Joint Photographic Experts Group. Used to refer to the standard they developed for still-image compression, which is sanctioned by the International Standards Organization (ISO).
- A stand-alone device that can hold several optical disks or magnetic tapes at a time, making it possible to switch among them at will.
- LCSH. A controlled vocabulary of terms commonly used to retrieve library materials.
- An Internet mail program, which distributes copies of e-mail messages to the subscribers of a mailing list.
- Process that reduces the storage space needed for an image file without loss of data. If a digital image that has undergone lossless compression is decompressed, it will be identical to the digital image before it was compressed. Document images (i.e., in black and white, with a great deal of white space) undergoing lossless compression can often be reduced to one-tenth their original size; continuous-tone images under lossless compression can seldom be reduced to one-half or one-third their original size.
- A process that reduces the storage space needed for an image file. If a digital image that has undergone lossy compression is decompressed, it will differ from the image before it was compressed (though this difference may be difficult for the human eye to detect). The most effective lossy-compression algorithms work by discarding information that is not easily perceptible to the human eye.
- Lempel-Ziv-Welch. A proprietary lossless data-compression algorithm.
- Multi-purpose Internet Mail Extensions. A standard for embedding multimedia data in e-mail messages.
- Motion Picture Experts Group. Used to refer to an image-compression scheme for full-motion video they developed, which is ISO-sanctioned. MPEG takes advantage of the fact that full-motion video is made up of many successive frames, often consisting of large areas that don't change, such as blue sky background. MPEG "differencing" notes differences, or lack of them, from one frame to the next.
- The arrangement of computers and storage devices on a network. Different topologies will create higher use on various segments of the network.
- An Internet discussion group devoted to a particular topic.
- Data or undentifiable marks picked up in the course of scanning or data transfer that do not correspond to the original.
- On-line public access catalog. A common term for automated, computerized library catalogs, made available to a wide range of users.
- The set of colors that appear in a particular digital image. Becomes part of a color look-up table. see Adaptive palette and System palette
- Computer-based recognition of forms or shapes within an image.
- A popular storage method for digital images. In the basic Kodak PhotoCD configuration, five different levels of image quality are stored for each image in an Imagepac.
- A sophisticated software program, produced by Adobe Systems, for editing and processing of images.
- Macintosh Picture. A storage format for digital images designed primarily for the Macintosh.
- The picture elements that make up an image, similar to grains in a photograph or dots in a half-tone. Each pixel can represent a number of different shades or colors, depending upon how much storage space is allocated for it.see 8-bit image or 24-bit image
- Techniques ensuring that high quality is maintained through various stages of a process. For example, quality control during image capture might include comparing the scanned image to the original and then adjusting colors.
- A compression scheme for moving and still images. Originally designed for Macintosh computers.
- Redundant Array of Inexpensive/Independent Disks. A storage device that uses several disks working together to provide large storage capacity and redundant backup. The use of a set of cheap small disks instead of a single large disk.
- see Bit-mapped image
- Number of pixels (in both height and width) making up an image. The higher the resolution of an image, the greater its clarity and definition.
- The number of dots per inch, dpi, used to display an image on a display device (monitor) or in print.
- Red Green Blue. An additive system for representing the color spectrum using combinations of red, green, and blue. Used in video display devices.
- A device for capturing a digital image. see Copystand, Drum, Flatbed, and Slide scanner
- see Image capture
- A scanner with a slot to insert 35-mm slides; usually capable of scanning only 35-mm transparent material.
- Still Picture Interchange File Format, proposed by ISO JTC 29, WG1 as a standard file format.
- Vocabularies that make scholarly communication and access to information more consistent.
- Using an algorithm to derive a lower-resolution digital image from a higher-resolution image (for example, eliminating every other pixel in each direction). see Derived image
- A file storage format used widely on Sun-3 computers.
- A representation, usually in photographic form, used for study.
- A color palette chosen by a computer system and applied to all digital images.
- TrueVision Targa file. A storage format for bit-mapped video images.
- TGN. One of three structured vocabularies produced by the Getty Art History Information Program (AHIP), TGN is a hierarchical arrangement of more than 300,000 of the world's place names, in vernacular languages and English, and in ancient and modern forms. Available on CD-ROM from the Getty Art History Information Program.
- see Browse image
- Tagged Image/Interchange File Format. A file-storage format implemented on a wide array of computer systems. Considered an industry standard, but so open that header information is used in many different ways.
- Generally refers to 24-bit (or better) images.
- ULAN. One of three structured vocabularies produced by the Getty Art History Information Program, ULAN comprises 200,000 variant names referring to approximately 100,000 artists. Published in print and electronic forms by G.K. Hall.
- Uniform Resource Locator. A standard addressing scheme used to locate or reference files on the Internet. Used in World Wide Web documents to locate other files. A URL gives the type of resource (scheme) being accessed (e.g., gopher, ftp) and the path to the file. The syntax used is: scheme://host.domain[:port]/path filename
- Universal Resource Name/Number. A storage-independent scheme under development to name all resources on the Internet, which is likely to be adopted by the Internet Engineering Task Force by late 1996. URNs are likely to supersede URLs (Universal Resource Locators) for identification and referencing of networked resources.
- A digital image encoded as formulas that represent lines and curves.
- An image-capture device that employs a video camera attached to a circuit board in a computer which converts the video signal into a digital file. Also called a frame-grabber.
- Optical disk storage medium for video images. Can store 108,000 still images.
- Bits altered within an image to create a pattern which indicates proof of ownership. Unauthorized use of a watermarked image can then be traced.
- WWW. An interconnected network of electronic hypermedia documents available on the Internet. WWW documents are marked up in Hypertext Markup Language. Cross references between documents are recorded in the form of URLs.
- Enlarging a portion of an image in order to see it more clearly or make it easier to alter. Opposite of zoom-out, which is useful for viewing the entire image when the full image is larger than the display space.
Howard Besser and Jennifer Trant, Introduction to Imaging: Issues in Constructing an Image Database
The Getty Art History Information Program Imaging Initiative
Copyright 1995. The Getty Art History Information Program, an operating program of the J. Paul Getty Trust. All rights reserved.