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average picture level (APL): In video systems, the average level of the picture signal during active scanning time integrated over a frame period; defined as a percentage of the range between blanking and reference white level.
block distortion : In the received image in video systems, distortion characterized by the appearance of an underlying block encoding structure.
blurring : In video systems, a global distortion, characterized by reduced sharpness of edges and limited spatial detail.
color errors : In video systems, distortion of hues in all or a portion of the received image.
continuous presence : In teleconferencing, the concurrent presence of two or more video images, such as two images that may appear on a single monitor on a split screen or on two separate monitors.
contrast : In display systems, the relation between (a) the intensity of color, brightness, or shading of an area occupied by a display element, display group, or display image on the display surface of a display device and (b) the intensity of an area not occupied by a display elements, a display group, or a display image. Deprecated synonym brightness ratio.
control field : In a protocol data unit (PDU), the field that
(a) contains data interpreted by the receiving destination logical-link controller (LLC)
(b) may be the field immediately following the destination service access point (DSAP) and source service access point (SSAP) address fields of the PDU. |
edge busyness : In a video display, distortion that is concentrated at or near the edge of objects, and that is categorized further by its temporal and spatial characteristics.
error blocks : In video systems, a form of block distortion in which a block or blocks in the received image bear no resemblance to the current or previous scene and may contrast greatly with adjacent blocks.
field : In an interlaced, raster-scanned video display, a partial frame, consisting of every nth scanning line of a complete frame, where n is an integer equal to the number of fields (usually two) in a complete frame.
frame : In video display, the set of all picture elements that represent one complete image. In NTSC and other television standards used throughout the world, a frame consists of two interlaced fields, each of which has half the number of scanning lines, and consequently, half the number of pixels, of one frame OR, in video display, one complete scanned image from a series of video images, usually composed of two interlaced fields.
freeze frame : A frame of visual information that is selected from a set of motion video frames, and is held in a buffer. Contrast with still video.
freeze frame television : Television in which fixed ("still") images are transmitted sequentially at a rate far too slow to be perceived as continuous motion by human vision. Note: Transmission of an image is usually performed periodically by a processing unit that contains memory in which data representing the image are stored. For an image of specified quality, e.g., resolution and color fidelity, freeze-frame television has a lower bandwidth requirement than that of full-motion television.
image : In the field of image processing, a two-dimensional representation of a scene. Synonym picture.
interlaced scanning : In raster-scanned video displays, a scanning technique in which all odd-numbered scanning lines are first traced in succession, followed by the tracing of the even-numbered scanning lines in succession, each of which is traced between a pair of odd-numbered scanning lines.
The pattern created by tracing the odd-numbered scanning lines is called the "odd field" , and the pattern created by tracing the even-numbered scanning lines is called the "even field" . Each field contains half the information content, i.e., pixels, of the complete video frame.
Image flicker is less apparent in an interlaced display than in a noninterlaced display, because the rate at which successive fields occur in an interlaced display is twice that at which successive frames would occur in a noninterlaced display containing the same number of scanning lines and having the same frame refresh rate.
Synonym interlacing.
jerkiness In a video display, the perception, by human vision faculties, of originally continuous motion as a sequence of distinct "snapshots." Note 1: The perception of continuous motion by human vision faculties is a manifestation of complex functions, i.e., characteristics, of the eyes and brain. When presented with a sequence of fixed, i.e., still, images of sufficient continuity and at a sufficiently frequent update rate, the brain interpolates intermediate images, and the observer subjectively appears to see continuous motion that in reality does not exist. Note 2: For example, the update rate of NTSC television displays is 30 frames (60 fields) per second.
mosquito noise : In a video display, distortion sometimes seen around the edges of moving objects, and characterized by moving artifacts around edges and/or by blotchy noise patterns superimposed over the objects, resembling a mosquito flying around a person's head and shoulders.
motion compensation : Interframe coding that (a) is used to compress motion of video images and (b) uses an algorithm to examine a sequence of image frames to measure the difference from frame to frame in order to send motion vector information.
motion response degradation: The deterioration of motion video quality, resulting in a loss of perceived spatiotemporal resolution.
object : In image processing, a sub-region of an image that is perceived as a single entity. Note: An image can contain more than one object.
panning : In video technology, the use of a camera to scan a subject horizontally. 3. In antenna systems, successively changing the azimuth of a beam of radio-frequency energy over the elements of a given horizontal region, or the corresponding process in reception.
p × 64 : In video teleconferencing, pertaining to a family of CCITT Recommendations, where p is a non-zero positive integer indicating the number of 64 kb/s channels. (188) Note: The p × 64 family includes CCITT Recommendations H.261, H.221, H.242, H.230, and H.320. These Recommendations form the basis for video telecommunications interoperability.
quarter common intermediate format (QCIF): A video format defined in CCITT Recommendation H.261 that is characterized by 176 luminance pixels on each of 144 lines, with half as many chrominance pixels in each direction. (188) Note: QCIF has one-fourth as many pixels as the full common intermediate format.
scene cut : Video imagery in which consecutive frames are highly uncorrelated.
scene cut response : In video systems, the perceived impairments associated with a scene cut.
smearing : In video displays, a localized distortion over a sub-region of the image, characterized by reduced sharpness of edges and spatial detail..
snow : In video display systems, noise that (a) is uniformly distributed on the display surface, such as that of a television or radar screen, (b) has the appearance of a uniform distribution of fixed or moving spots, mottling, or speckling, and (c) is usually caused by random noise on an intensity-modulated signal in a display device, such as a cathode-ray tube.
spatial application : An application requiring high spatial resolution, possibly at the expense of reduced temporal positioning accuracy, i.e., increased jerkiness. Note: Examples of spatial applications include the requirement to display small characters and to resolve fine detail in still video, or in motion video that contains very limited motion.
spatial edge noise : In a video display, that form of edge busyness that is characterized by spatially varying distortion that occurs in close proximity to the edges of objects.
still image : Nonmoving visual information, i.e., fixed images, such as graphs, drawings, and pictures.
still video : Video imagery that is not intended to convey the appearance of movement. Contrast with freeze frame, freeze frame television.
temporal application : A video application requiring high temporal resolution, i.e., reduced jerkiness, possibly at the expense of reduced spatial resolution. Note: An example of temporal applications is the ability to accurately discern moving image features such as facial expressions and lip movements.
temporal edge noise : In a video display, that form of edge busyness that is characterized by time-varying sharpness at the edges of objects.
transmission service channel : In video systems, the one-way transmission path between two designated points.
videophone : A telephone that is coupled to an imaging device that enables the call receiver or the call originator, or both, to view one another as on television, if they so desire.
videophone (military) : A military communications terminal that (a) has video teleconference capability, (b) is usually configured as a small desktop unit, designed for one operator, and (c) is a single, integrated unit.
windowing : Sectioning of a video display area into two or more separate regions for the purpose of displaying images from different sources. (188) Note: In windowing, one window could display data, another motion video from a remote site, and another, graphics.
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