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Refers to a way of representing bitmap or other data that can handle up to 16 (2^4) colors.
Refers to a way of representing bitmap or other data that can handle up to 256 (2^8) colors.
Tape backup format and medium. Video recording format and medium, usually used for home use due to the compact size of the physical medium, and not considered of broadcast quality. See VHS and Beta.
Refers to a way of representing bitmap or other data that can handle up to 32,768 (2^15) colors.
Refers to a way of representing bitmap or other data that can handle up to 65,536 (2^16) colors.
Refers to a way of representing bitmap or other data that can handle up to 16,777,216 (2^24) colors.
A video display card with active components designed to enhance or speed up the display of image data sent to it by a rendering application. Contrast with dumb frame buffer.
An electronic device with which the user must constantly interact in order to obtain information. Video arcade games and most multimedia applications are active information devices. Contrast with passive information device.
An algorithm that has no certain prior knowledge about the format of the data it is encoding. It must adapt to the format of the data as it encodes it. LZW is an adaptive encoding algorithm.
A color system in which colors are created by adding colors to black. The more color that is added, the more the resulting color tends toward white.
Artifact produced on a pixel-based output device where diagonal or curved edges appear jagged.
An additional channel of bitmap data used to store transparency data for an image, which can be on a per-pixel, per-block, or per-image basis. The degree of pixel transparency for an 8-bit alpha value ranges from 0 (the pixel is completely invisible or transparent) to 255 (the pixel is completely visible or opaque). See also overlay bit.
A sequence of two or more images displayed in a rapid sequence so as to provide the illusion of continuous motion. Animations are typically played back at a rate of 12 to 15 frames per second.
The process of reducing artifacts by interpolating intermediate colors perpendicular to an aliased edge.
A shadow mask with vertical strips instead of round holes. See Trinitron, shadow mask, and dot pitch.
An ordered set of colored display elements on an output device. This term is used loosely to refer to an array of numerical values used by an application program to specify colored elements on an output device.
A method of compression developed by the Johnson-Grace company.
A detectable change in an image produced by a rendering application, such as a filter, or an editing tool, such as a paint program. Such changes are said to be introduced by human intervention and are therefore artifactual influences upon natural, ecofactual data.
The proportional measurement of an image or pixel based on its horizontal and vertical size. For example, an image with an aspect ratio of 4:3 has a horizontal width that is 4/3 of the vertical height.
See strip.
Horizontal, vertical, or, more rarely, diagonal bands of discoloration inadvertently placed in an image during creation or rendering.
Bulletin Board System. A telecommunications program running on a computer that allows other computers with modems to dial in and access files. BBSs are a prime source of image files and file format information. Older names for BBSs include Computer Bulletin Board System (CBBS) and Electronic Bulletin Board System (EBBS).
Video recording format and medium, considered to be of superior quality to VHS but not widely used. Not considered broadcast quality. See VHS.
Broadcast quality video recording format and medium. See Beta, VHS, U-Matic, M-II, and D-2.
A smooth curve specified by a small set of values, including tangent and control point information.
An image that contains only two colors: a background color and a foreground color. See monochrome and halftone.
Refers to systems or machines that store the most significant byte (MSB) at the lowest address in a word, usually referred to as byte 0. Contrast with little-endian.
The size of a value used to represent a pixel in bitmap graphics data. This is usually stated as the number of bits making up the individual data value, or sometimes the number of bytes. The number 2 raised to the power bit depth specifies the maximum number of values the pixel can assume. Same as pixel depth.
The order of the bits within a byte. The first bit in a byte may be either the most significant or the least significant bit. See also LSB and MSB.
A 2D array of bits one bit deep. A bitmap containing pixels with a depth of eight bits may be said to contain eight bit planes. A monochrome image (one bit per pixel) is usually stored as a single bit plane.
The state of a bit (0 or 1).
A set of numerical values specifying the colors of pixels on an output device. In older usage, the term referred to data intended for display on an output device capable of displaying only two levels. It is used in this book as a synonym for raster.
The portion of a bitmap file containing information associated with the actual image.
A representation of a graphics work on a raster device or in a bitmap file. Redundant in our terminology.
See bi-level.
See bit depth.
See chunk.
Same as bits per pixel.
Video recording medium retaining sufficient quality after multiple edit and copy operations to be broadcast on commercial television.
The order of bytes within a word of data. The first byte in a word may be either the most significant or least significant byte. See also big-endian, little-endian, LSB, and MSB.
Bit depth expressed in bytes.
See Computer Aided Design.
Charge coupled device. An array of electronic components which convert light into electrical signals. Used in scanners and video cameras. See scanner.
International Telegraph and Telephone Consultative Committee. See ITU.
See Compact Disc.
Compact Disc-Digital Audio. The standard used for encoding audio data onto a compact disc.
Compact Disc-Interactive. The standard used for encoding audio and video information onto compact discs for use in interactive multimedia systems.
Compact Disc-Recordable. The standard for creating write-once compact discs that may be mastered on a standard PC.
Compact Disc-Read-Only Memory. A compact disc containing data encoded using the CD-XA standard. See also CD-XA and ISO-9660.
Compact Disc-Extended Architecture. The standard used for encoding data onto what we know as a CD-ROM. See also ISO-9660.
Term used when referring to color. Same as chrominance.
The process of creating an image, a portion of which is placed on a background of uniform color, usually blue, so that another image can later be added by placing it in the area of uniform color.
The color portion of an image. It is the mixture of hue and saturation, or the combination of three primary colors, such as red, green, and blue.
A collection of data with a known format within a graphics file. Chunks are also called blocks in some graphics file format specifications. See also packet.
The breaking up of a block of data into two or more smaller pieces, usually to accommodate memory limitations or to avoid hardware dependencies.
International Commission on Illumination (Commission Internationale de l'E'clairage). The CIE established an international standard for primary colors in 1931. This standard allows all colors to be defined as a weighted sum of three primary colors.
Color Look-Up Table. See look-up table.
Acronym for Cyan/Magenta/Yellow. A subtractive color system based on the primary colors cyan, magenta, and yellow.
Acronym for Cyan/Magenta/Yellow/Key. A subtractive color system based on the primary colors cyan, magenta, and yellow. Key color is the color black, which is not reproducible using the CMY model alone.
Shortened version of encoder/decoder (similar to modem for modulator/demodulator). A codec is any hardware device or set of software algorithms that can encode data and decode it back to it original (lossless) or reasonably original (lossy) state.
The process of determining and adjusting the properties of a display device or the colors in an image to ensure that the rendered image is accurate to some standard, usually the human eye.
One of the numerical elements used to specify a color in a particular color model when that color is specified using an ordered n-tuple. Green is one channel in the RGB color model, which is specified using the ordered triplet (R,G,B).
A section of a file for the storage of information designed to help a rendering application in displaying an image on a particular output device or class of output devices different from that assumed by the creator application.
A system by which colors are specified, usually by numerical values or ordered sets of numbers.
The range of colors which can be displayed using a particular color model or output device.
See look-up table.
Image data whose colors are not stored in the bitmap itself, but in a separate data array.
The way colors are broken down and specified in a particular application or system.
A section of a file holding information about one color component of the color model currently in use.
When a particular color scheme uses an ordered n-tuple to specify color, all the possible values corresponding to colors can be plotted on an n-dimensional graph. All the points plotted, which correspond to colors in the color model, constitute the color space.
See look-up table.
Same as pixel values.
A circular plastic disc used for the storage of audio, video, textual, and other data that can be represented in a digital form, and from which data can be retrieved using an optical process. Although there are various formats, the one in most common use is 4.75 inches (12 centimeters) in diameter. See also CD-ROM.
Color video information transmitted using three separate signal channels. RGB, YIQ, and YUV are examples of component video signals.
A color specified in a color model where that color is specified using an ordered n-tuple. A system where more than one color channel value exists, and where more than one channel value is needed to specify the color.
An image formed of two or more subimages stored separately in a file. Sometimes refers to a bitmap image with a lot of color variation per unit area.
Color video information transmitted using a single signal channel. NTSC, PAL, and SECAM are examples of composite video signals.
Spurious addition to or degradation of an image due to the process used to compress or decompress it.
The algorithm or family of algorithms used by the creator application in producing the file.
The use of applications, usually vector-based, for the design and rendering of graphical data of architectural and mechanical drawings, electronic schematics, and 3D models. Commonly referred to as CAD.
Image data stored as a continuous block of pixel values without scan-line or block delimiters.
An image consisting of smooth gradations of color between adjacent elements, requiring an output device capable of displaying thousands or millions of colors at high resolution in order to prevent image artifacts.
A file format version created by an application vendor to accommodate a bug or quirk in a program. This is sometimes caused by ignorance or honest error, but in many cases is intentional. There is ample evidence that at least one vendor, the custodian (but not the originator) of a file format specification, knowingly released format revisions so as to avoid shipping delays caused by bugs introduced by junior programmers.
The process of transforming the value of a pixel, or a field of pixels, based on a mathematical formula. Convolution is used to alter the color of an image (filtering), or to re-encode the data (compression).
The exclusive rights to the production, publication, and sale of a work of authorship, such as a photograph or a captured image.
Cyclic Redundancy Check. An algorithm that recursively generates a 16- or 32-bit numerical value based on a stream of data. The value can be used to verify whether the data has changed. See digital signature.
Broadcast quality video recording format and medium. See Beta, VHS, U-Matic, M-II, and Betacam.
The process of converting data from one format to another format that is physically smaller in size. The same logical information is stored using less physical information.
Typically the smallest units of readable data with a collection of data. Bits, bytes, WORDs, and DWORDs are all data elements.
A generic term for the process of converting data from one format to another. Data compression and data encryption are both forms of data encoding.
The process of converting data from an intelligible format to an unintelligible, but decryptable, format.
Discrete Cosine Transform. A mathematical transform used to convert data from a 3D to a 2D form. Used by lossy compression methods such as JPEG and MPEG.
Device Dependent Bitmap. A bitmap format designed to support the capabilities of a specific type of display hardware. A bitmap format not designed with portability in mind.
The process of throwing away portions of a bitmap image when reducing it in size.
An algorithm that converts encoded data to a raw format.
Device Independent Bitmap. A bitmap format that is designed not to be limited by the capabilities of a specific type of display hardware. A portable or interchange data format.
A light producing mechanism which concentrates and directs visible light but not infrared radiation (heat). Used in movie and multimedia production, and in some scanners. See scanner.
An input device in the form of a camera, capable of delivering bitmap image data of real-world scenes in digital form to a creator application.
An electronic method of verifying the authenticity of a message or file. A block of data is attached to the message that can be used to validate who sent the message and when it was sent. If a change is made to the file, the signature will not verify.
The process of converting an analog signal to a digital signal. See sampling.
A device that creates a version of a physical graphical representation by creating a digital version. Common digitizing devices are scanners, image capture boards that work with video cameras, and digital cameras.
An input device incorporating a pen-like component and a flat surface, and meant to provide a simulation of the interaction between the hand, a pen or pencil, and paper. Can be pressure-sensitive.
See video display card.
The portion of an output device where an image appears. The screen of a monitor, or printed paper.
The process of displaying colors not available on an output device. Patterns of other colors are created by intermixing monochrome pixel values with color pixels to produce shading and highlighting that appears to the eye as differing colors. See monochrome and contrast with halftone.
The measure of the spacing between the centers of physical pixels on an output device, usually a monitor. On monitors, dot pitch is expressed in millimeters (mm) between the centers of like-colored pixels. See shadow mask.
Where the most significant bit (MSB) is the first bit read in a byte. See MSB.
The area on an output device where a rendered image appears.
A high-resolution scanning device used in the most demanding professional applications. They can often be the source of extremely large files. See scanner and film scanner.
A video display card consisting mainly of a frame buffer with few enhancements. Contrast with accelerator card.
See Electronic Document Image Processing.
A subfield of image processing specializing in the creation, storage, and manipulation of black-and-white images derived from printed documents. At least 75 percent of the image-processing market today is based on EDIP systems and applications.
Information, such as color, line width, pen style, and fill color, stored in a file for use by a rendering application in reconstructing an image element.
An algorithm that converts raw data to an encoded form, usually to physically compress the data.
See lossless encoding.
Graphics files produced by a program that manages FAX-modem hardware. These are generally bitmap files and may be compressed. They are often in a proprietary format, although versions of TIFF and PCX are popular.
A fixed-size data structure in a file.
Images stored in a video or animation file designed to support various display technologies. NTSC video consists of two sets of images meant to be displayed alternately, each of which is a field.
The smallest unit of logical information within a file. Examples include fields within graphics file headers and color triples used to store RGB pixel data.
A data structure containing information on the data stored within a file. Graphics file headers contain information such as the height and width of an image and the number of bits per pixel.
See file identifier value.
A specific value, or set of values, used to positively identify a file as being of a particular file format. File ID values may be an integer, such as 59A66A95h, or a string of ASCII characters, such as BITMAP, and they usually appear in the first field of a file header. Also called magic number.
Fill color and/or other information associated with an image element, and used by the rendering application to reconstruct an image.
A color meant to be used by a rendering application when filling a closed area, usually polygonal, when reconstructing an image element.
See padding.
See slide scanner.
A section of code or program which operates on an entire block of data. Contrast with scanner.
Refers to an element in a file that has a known position, usually identified by an offset from a landmark in a file.
A monitor or other output device with fixed frame rate and horizontal frequency, only capable of displaying a small set of resolutions. See horizontal frequency and frame rate.
A data structure similar to a header but appended to the end of a file.
The person or organization responsible for the definition of the physical structure of, and conventions associated with, a file format. Often this person is a programmer called on to produce a file format in association with an application. In some cases, the format creator is a standards committee.
Repetitious patterns that naturally occur in the texture of all surfaces. Mathematics is used to described the properties of fractals.
The use of fractal encoding to reduce the amount of physical data required to store an image. See fractal encoding.
The process of describing a bitmapped image as a sequence of fractals and by its fractal properties. See fractal.
A single image. Multiple frames of slightly differing images displayed in rapid sequence are used to create animations.
Older term for video display card. Technically, the portion of a video display adapter containing memory in which digital image data is assembled prior to sending it to a monitor. See video display card.
Number of full images which can be displayed by an output device, usually a monitor. Number of fields a monitor can display in a given time. Usually expressed in hertz (Hz). See fields, interlaced, non-interlaced, and vertical retrace.
Series of single images stored in a video, animation, or multimedia format file, meant to give the illusion of motion when rendered in rapid succession.
Factor that determines the quality of the image a monitor or other output device can display. Higher frequency monitors update the screen faster and theoretically can display more information in a given amount of time. See vertical retrace, interlaced, and non-interlaced.
File Transfer Protocol. A low-level protocol used to transfer files between computers over computer networks. FTP is the primary means by which binary files are transferred between machines on the Internet.
A term sometimes used to imply that a device is capable of displaying 2^15 (32,768) or 2^16 (65,536) colors; however, this actually describes hicolor; fullcolor tends to be a marketing term, rather than a technical one.
Video image frames displayed at a rate of 30 frames per second for NTSC and 25 frames per second for PAL.
A sub-discipline of mathematics used to quantify subjective linguistic concepts, such as bright, dark, very far, quite close, most usually, almost impossible, etc.
Abbreviation for CCITT Group 3 encoding.
Abbreviation for CCITT Group 4 encoding.
A numerical value used to indicate the non-linear response curve of an output device to light intensity. Used to correct the intensity of an image on a display device (gamma correction). Also called gamma value.
An elaboration on a fill color consisting of two colors placed at opposite ends of a closed area of an image element. The area is filled with a continuous blend of color intermediate to the two colors and between the two ends. See fill color.
The end result of effort by a graphic artist. A drawing or other artifact.
See video display card.
See video display card.
Data which may or may not have a physical representation, intended for display on an output device.
A file containing graphics data.
The definition of, and conventions associated with, a file structure used for the storage of graphics data.
In older terminology, raster data composed of values with more than two levels, intended for an output device capable of displaying only shades of gray.
A term used when referring to an image. A gray shade is any color whose three primary colors are the same value. Gray shades only have intensity (luminance) and no color (chrominance).
The use of bi-level pixels or dots to create the appearance of shades of gray by grouping the pixels in patterns that produce the desired shades. Used in printing and liquid crystal displays. See bi-level and contrast with dithering.
Acronym for Hue/Brightness/Luminosity. See HSI.
A set of rules derived from experimentation or experience.
Video recording format offering resolution of over 400 lines. See VHS, S-VHS, 8-mm, and Beta.
A term used to imply that a device is capable of displaying 2^15 (32,768) or 2^16 (65,536) colors.
Acronym for Hue/Lightness/Saturation. See HSI.
Measure of the speed at which the electron beam in a monitor sweeps across the width of the active area of the screen. Usually expressed in kilohertz (kHz).
Acronym for Hue/Saturation/Brightness. See HSI.
Acronym for Hue/Saturation/Intensity. An additive color system based on the attributes of color (hue), percentage of white (saturation), and brightness (intensity). Similar or identical color systems include HBL, HLS, HSB, HSL, and HSV.
Acronym for Hue/Saturation/Luminosity. See HSI.
Acronym for Hue/Saturation/Value. See HSI.
Any color, such as red, violet, orange, and so on.
The storage and display of bitmap and textual data using a single graphics file format. GIF89A is an example of a format with a hybrid text capability.
The ability to store complex and highly organized database information in conjunction with graphical data. See also hybrid text.
A collection of graphical and textual data organized in such a way as to facilitate easy access to all of the information it contains. Hypertext may be thought of as a precursor to multimedia, or simply as an extension of it. Certain extensions of hypertext are becoming known as hypermedia.
A small bitmap image used as a placeholder to represent an object. An icon may also be though of as a graphical file name. Contrast with thumbnail image.
See file identifier value.
International Electrotechnical Commission. See ISO.
A visual representation of graphics data displayed on the display surface of an output device. Output of a rendering application. One end of the graphics production pipeline. A single frame from an animation or video sequence.
See bitmap image.
A term used loosely to refer to bitmap data, or the portion of a bitmap file containing bitmap data.
Portions of an image, often repeated, from which the image is composed by duplication, rotation, scaling, and translation.
Image offset table. An area of a file designed to hold descriptions of subimages, image components, or individual images in a multi-image file.
The vertical size of an image, usually expressed in pixels or scan-lines or other non-device-dependent units.
The horizontal size of an image, usually expressed in pixels or other non-device-dependent units.
A portion of a file designed to hold offsets, usually measured in bytes, where subimages, image components, or individual images in a multi-image file can be found.
See look-up table.
Pairs of numbers arranged in a table so that an application can match numbers it knows about to numbers representing colors that an output device knows about.
See color-mapped image.
The specification of colors through the use of a palette or look-up table.
Generic term in computer technology referring to any data which is processed or transformed.
The creation of encoded data from two or more image frames. MPEG encoding is an interframe encoding method.
Refers to a strategy used by televisions and some older monitors, where the electron gun draws every other line during a single sweep across the active area of the screen. The alternate lines are filled in during a second pass. See vertical retrace, non-interlaced, and fields.
See interleaved encoding.
The storage of bitmap scan-lines, or pixels within scan lines, in a non-sequential pattern. Contrast with sequential encoding.
In reference to a single image, the storage of two or more subimages which are combined to create a final image by displaying alternate scan-lines from each subimage. In reference to video, multimedia, or animation formats, the process of storing or displaying information other than that used to reconstruct the video portion between video frames.
The addition of pixels between pairs of others. Usually made necessary when enlarging a bitmap.
The creation of encoded data from a single image frame. JPEG encoding is an intraframe encoding method.
International Standards Orgainzation. The primary organization for creating world-wide technical standards. Along with the IEC and the ITU, the ISO authors and maintains standards for everything from nuts and bolts to computer languages.
A file system standard developed for CD-ROMs using the CD-XA encoding standard. An ISO-9660 file system is readable by many operating systems, including MS-DOS, Macintosh OS, and UNIX.
International Telecommunications Union. An agency of the United Nations responsible for telecommunications. The ITU replaced the CCITT on Februrary 28, 1993.
ITU Telecommunications Standardization Sector. The body within the ITU responsible for setting world telecommunications standards (Recommendations).
Term denoting the presence of aliasing in an image.
Joint Bi-level Image Experts Group. The ISO/IEC JTC1/SC29/WG9 and CCITT SGVIII group formed in 1988 to establish a standard for the progressive encoding of bi-level image data. JBIG is also the name given to the codec created by this group.
Joint Photographic Experts Group. The group of the ISO responsible for the creation and maintenance of the JPEG still-image compression standard.
Joint Technical Committee 1. A group within the ISO/IEC that handles information technology.
Points necessary for the reconstruction of a graphics object from vector data. These are usually the minimum needed to specify the object. Two points at the corners of a rectangle are the key points.
Refers to an element in a file from which other positions and offsets are calculated. The canonical landmarks are the beginning, end, and current position. Other features, such as prominent data structures, may at times act as landmarks.
Recording medium used for video, similar to a large CD or CD-ROM, offering the advantage of random access and high quality.
Image artifact, usually generated from vector data, produced by a rendering application from an image element incorrectly designated as closed. Usually consists of horizontal lines of the fill color in an inappropriate area of the image.
Refers to systems or machines which store the least significant byte (LSB) at the lowest address in a word, usually referred to as byte 0. Contrast with big-endian.
Idealized pixels having perfectly defined characteristics and occupying no physical extent. The graphics equivalent of a mathematical point. Contrast with physical pixels.
A series of pairs of numerical values whereby a program can match a meaningful value to one which specifies a color on an output device.
A data compression or encoding algorithm that does not lose or discard any input data during the encoding process.
A data compression or encoding algorithm that loses, or purposely throws away, input data during the encoding process to gain a better compression ratio. JPEG is an example of a lossy encoding method.
Lines per inch, usually used to refer to screen size or the resolution of an output device. See screen.
The brightness or intensity of a color. The pixels in a monochrome image have a luminance of either 100 percent or 0 percent.
Depending on context, either the least significant byte (of more than one juxtaposed bytes) or the least significant bit (of the bits in a byte or word of data). Contrast with MSB.
See look-up table.
Broadcast quality video recording format and medium. See Beta, VHS, U-Matic, Betacam, and D-2.
See file identifier value.
Arbitrary numbers or text strings, often picked "out of the air" by a format creator for the purpose of identifying the format.
A family of algorithms used to create digital signatures.
Data comprised of attributes, parameters, notebooks, and other types of miscellaneous complex data aggregates associated with primary scientific data.
A file format capable of storing two or more types of image data, usually vector and bitmap, in the same file.
Acronym for Musical Instrument Digital Interface. A standard for digital signals used to control electronic musical instruments. MIDI information may be stored as a data file and is found in many multimedia file formats.
Modified Modified READ, The compression algorithm used in CCITT Group 4 facsimile compression.
An image composed of a single color and black. Most monochrome images are black and white, although any color might be substituted for white. Also called 1-bit images. Although the term monochrome, of course, means single-colored, in computer graphics it is used to denote a system where two colors can be specified: the foreground color and the background.
Motion Picture Experts Group. The group of the ISO responsible for the creation and maintenance of the MPEG video compression standard.
Modified READ, The compression algorithm used in CCITT Group 3 facsimile compression.
Depending on context, either the most significant byte (of more than one juxtaposed bytes) or the most significant bit (of the bits in a byte or word of data). Contrast with LSB.
A palette with two or more individual color values per color element. Contrast with single-color palette.
A monitor or other output device with frame rate and horizontal frequency adaptable to demand. See horizontal frequency, fixed frequency, and frame rate.
The concept of creating, storing, and playing back two or more forms of electronic information simultaneously. Such information includes still-images, motion-video, animations, digitized sound, and control information such as MIDI codes.
Refers to a strategy used by higher-frequency monitors where the electron gun draws all lines of the active area of the screen during a single sweep. See interlaced, vertical retrace, and fields.
Acronym for National Television Standards Committee. The standards committee responsible for, among other things, the creation of the color television signal used in the United States (NTSC video).
Image elements, particularly in vector files. Descriptions of complex image elements. Image element information stored along with code for use by the rendering application.
Generic term in computer technology meaning the result of any process or transformation of data.
Physical mechanism used to create a display.
A computer language or set of commands created by a vendor to communicate with a particular output device, such as a printer. Hewlett Packard's PCL is one well-known output device language and is understood by Hewlett Packard printers and HP-compatible printers. It may or may not be easily human-readable. See page description language.
A condition which results when data of a certain size is placed in a storage cell, such as location in memory or a register, which is too small to hold it. This is usually a problem resulting in loss or corruption of data.
An additional bit found in a pixel or pixel plane that indicates whether the pixel is displayed as visible (opaque) or transparent (overlayed). See alpha channel.
A block of data with a known structure, usually used to denote elements of a stream.
Portion of a file usually included to accommodate machine dependencies or to increase reading or writing speed.
A computer language created by a vendor to communicate with output devices. It may be a fully functional language and is always human-readable. It is generally more sophisticated than an output device language and is not tailored to any particular output device. The most popular page description language in use today is Adobe's PostScript.
An array of offset values used to index the location of multiple bitmaps within a single graphics file. Each offset value indicates the starting position of each bitmap.
Acronym for Phase Alternation Line. PAL is a standard of color television and video signals developed in West Germany and used throughout Europe (PAL video).
The gamut of colors which a device can display; a software data structure used to match numbers that are meaningful to a software program to numbers that cause colors to appear on an output device.
An electronic device with which the user need not interact in order to obtain data. Television and newspapers are examples of passive information devices. Contrast with active information device.
Page Description Language. A computer language used for describing the layout, font information, and graphics of printed and displayed pages.
See pixel.
A logical device used by creator applications to draw lines or curves or objects composed of them, having the properties of width, color, and possibly line style. An area in a file holding information used by a rendering application in reconstructing lines.
A term often used in object-oriented technology to describe data that is stored in a static medium, such as a disk file or database. The data is said to "persist" even after the application that created it is no longer in memory. Spreadsheet, word processing, and graphics files are examples of persistent data.
Pretty Good Privacy. A powerful public-key encryption system authored by Phil Zimmermann that is freely available on the Internet.
The actual pixels which appear on the display surface of a raster output device. Contrast with logical pixels.
See pixel.
In traditional usage, short for "picture elements." These are irreducible elements of color created by an output device on its display surface. The term is sometimes used loosely to refer to the values of bitmap data elements used by an application to order the display of color elements on an output device.
See bit depth.
In older terminology, bitmap data composed of values with more than two levels, intended for an output device capable of displaying color.
Numerical data items in a graphics file indicating the color or other information associated with an individual pixel.
See pixelmap.
Image data stored as separate color planes, and meant to be assembled into the final image by the rendering application. Contrast with scan-line data.
Graphics files with image data stored as bit planes or color planes rather than as pixels.
A bitmap rendering of vector or 3D graphical data used to display an approximation of the graphical data. See thumbnail.
An algorithm that has certain prior knowledge about the format of the data it is encoding. Huffman is a predictive encoding algorithm.
A bitmap rendering of vector or 3D graphical data used to display an approximation of the graphical data. See thumbnail.
Colors in a particular color model from which other colors can be constructed. In the RGB color model, red, green, and blue are the primary colors because other colors can be produced by mixing them.
The series of operations involved in defining, creating, and displaying an image, from conception to its realization or recording on an output device.
The storage of a single bitmap as several different images, each at a different level of resolution.
A color specified through the use of a palette or look-up table.
The process of reducing the number of colors defined in the source data to match the number available on an output device.
Generally refers to features introduced in an image when the data used to render that image is converted to a data format capable of displaying fewer colors than the original. Banding and false color are two examples of possible quantization artifacts. Usually considered undesirable.
Refers to graphics data represented by color values at points, which taken together describe the display on an output device. Bitmap is used in preference to raster in this book.
Image data without header information. Sometimes refers to image data, especially bitmap data, which is uncompressed or otherwise unencoded.
Relative Element Address Differentiation code. A compression method used by CCITT Group 3 and 4 facsimile transmission.
The representation of an image on an output device. Sometimes meant to signify the current rendered version of some particular graphics data.
To produce a visual representation of graphics data on an output device.
The actual representation of an image on an output device.
The actual artifact produced as the end result of the computer graphics production process, which may be an image on a monitor or on paper.
Fields in a file designated in the format specification as reserved space.
Portion of a file designated in the format specification as space for additional information should it become necessary in the future.
The measure of detail within an image. The resolution of an image is its physical size (number of pixels wide by number of scan lines long). The resolution of a display is the number of scan lines it may display (800x600 is a higher resolution than 320x200).
Acronym for Red/Green/Blue. An additive color system based on the primary colors red, green, and blue. The RGB model is loosely patterned after human eyes, which have a peak sensitivity to the colors red, green, and blue light.
Run-Length Encoding. A simple method of compressing runs of identical byte sequence values into a code only a few bytes in length.
Video recording format and medium offering horizontal resolution of over 400 lines. See VHS and Beta.
The number of digital samples recorded per second. The sample rate increases with the number of samples recorded per second. Same as sample resolution.
See sample rate.
The process of reading an analog signal at specific increments in time (sample rate) and storing the data as digital values. Sampling is the basic process used to create digital audio and video.
The percentage of white in a color. Zero percent saturation is full white (no color). 100 percent saturation is no white (pure color).
An image, such as that stored as vector data, which can be scaled without introducing artifacts.
The process of enlarging an image in one or more directions.
A row of pixels. The term comes from the scanning action of raster CRT output devices, which produces successive lines of output on the display surface.
Image data stored as scan lines, and meant to be displayed a line at a time by the rendering application. Contrast with planar data.
An array of offset values used to index the location of each scan line or tile within a collection of bitmap data, which may or may not be compressed. Each offset value indicates the starting position of each scan line or tile.
An input device generating a bitmap image of a surface. A section of code or program allowing random access to a block of data and which treats different portions of the block differently in accord with its informational content. Contrast with filter.
A computer language used to describe the position and attributes of objects within a 2D or 3D image. A file produced by such a language is called a scene format or scene description file.
Term borrowed from traditional graphics denoting a device or process designed to turn a continuous tone image into an array of dots, usually for display on a low-resolution output device. See LPI.
Acronym for Sequential Coleur Avec Memoire (sequential color with memory). SECAM is a standard of color television and video signals used in France and several other European countries (SECAM video).
An independent section of a data stream. For example, a JPEG data stream is composed of many different types of information, each stored in a separate segment.
The storage of a bitmap using the natural order of its scan lines from the top-to-bottom or bottom-to-top of image. Contrast with interleaved encoding.
A plate with tiny holes, usually in a monitor, which helps locate and focus the electron beam. The spacing of the holes in monitors with a shadow mask determines the dot pitch. See dot pitch.
A palette with one color value per element. Contrast with multi-channel palette.
A scanner which images an object in a single pass of its mechanism. See scanner, three-light method, and three-filter method.
A device allowing the digitization of slides taken with conventional film cameras. Usually much higher resolution devices than scanners designed with paper in mind. See scanner.
Data with no fixed position in a file, composed of sub-elements with a known structure.
A collection of one or more contiguous scan lines in a bitmap. Scan lines are often grouped in strips to buffer them in memory more efficiently. Also called bands in some file format specifications.
See aperture mask.
A file of character information meant to be rendered by drawing single lines, usually by a plotter or other device responding only to pen up, pen down, and move to commands.
See decimation.
A color system in which colors are created by subtracting colors from white. The more color that is added, the more the resulting color tends toward black.
A data structure in a file which can vary in both size and position.
Process whereby color images are produced, usually in scanners, by illuminating the object to be imaged with white light which is made to pass through three successive colored filters. Contrast with three-light method. See color model and scanner.
Process whereby color images are produced, usually in scanners, by successively illuminating the object to be imaged with three colors, usually red, green, and blue. Contrast with three-filter method. See color model and scanner.
A small image derived from a larger image used to quickly display an approximation of the contents of an image. See preview.
A 2D sub-section of a bitmap. For example, a bitmap 100x100 pixels in size may be divided into four 25x25 pixel tiles. Pixels are often grouped as tiles rather than scan lines to achieve a more efficient use of memory.
See footer.
Convert from one encoded data format to another encoded data format--for example, converting CCITT Group 3-encoded data to RLE-encoded data.
See convolution.
The degree of visibility of a pixel against a fixed background. A totally transparent pixel is invisible. See also alpha channel.
Color models that use three color channels to specify a color. The RGB color model is a trichromatic colorimetric system.
Trademark of Sony Corporation, referring to picture tubes used in monitors and televisions using aperture mask technology, and where dot pitch is an expression of the horizontal distance between strips in the aperture mask. See aperture mask, shadow mask, and dot pitch.
A scanner which images an object using three recording devices at once, usually CCDs. See scanner and CCD.
A term used to imply that a device is capable of displaying 2^24 (16,777,216) colors or more (said to match or exceed the color-resolving power of the human eye). Truecolor formerly referred to any device capable of displaying 2^15 (32,768) colors or more, but hicolor more accurately describes the display of 2^15 (32,768) or 2^16 (65,536) colors.
Broadcast quality video recording format and medium. See Beta, VHS, Betacam, M-II, and D-2.
Where the least significant bit (LSB) is the first bit read in a byte. See LSB.
Refers to graphics data composed mainly of representations of lines and outlines of objects, which can be compactly represented by specifying sets of key points. A program displaying vector data must know how to draw lines by interpolating points between the key points.
See frame rate.
The interval between when an electron beam in a monitor reaches the end of its sweep across the active area of the screen and when it returns to the start.
See frame rate.
Video recording format and medium in wide use in conjunction with television technology, offering horizontal resolution of 240 lines. Not considered broadcast quality. See Beta.
See video display card. Also, a device allowing output in NTSC, PAL, or other video format.
See video display card.
See video display card. Also, a video adapter which may have circuitry for controlling a video recording or playback deck.
Device which takes digital information from a rendering application and converts it to an analog format suitable for output on a monitor.
Data or an image that is produced, but that can't be seen--in other words, for which no physical representation yet exists. Data in a file.
A computer program that mimics a biological virus in its characteristics and actions, including hiding, replicating, and possibly causing the death of its host.
A 3D pixel. Voxels contain all of the components of a pixel (such as color values) and include an extra component that specifies the distance of the voxel from the point of observation.
Virtual Reality Modeling Language. An interpreted language used to render both still and animated 3D objects.
Video tape recorder used as an output device for video, animation, and multimedia creator applications.
The point in an image from which pixels are numbered in the horizontal direction. Usually at a corner or at the center of the image.
The point in an image from which to start counting scan-lines. Usually at the top, bottom, or center of the rendered image.
The color model used by NTSC video signals. See NTSC.
Acronym for Y-signal, U-signal, and V-signal, which is based on early color television terminology. A luminance/chrominance-base color model (Y specifies gray-scale or luminance, U and V chrominance) used by many video compression algorithms, such as MPEG.
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