This Glossary was originally compiled by dhomas trenn. What a mentsh!

  A/B Roll : An analog technique of recording from two source VCRs (A and B) to a third VCR, using a mixer to create transitions .

  Alpha Channel : A grayscale image used as a filter when compositing  two other images. The alpha channel is used between the two images and dictates what parts, and to what degree, the picture in behind shows through onto the front picture. The gray shade of each pixel  determines the amount of transparency, ranging from black (0%) to white (100%).

  Analog Video : A video signal where an infinite number of smooth steps is used to describe levels (colors).

  Antialiasing : A process used to reduce rough/jagged edges in computer images by blending colors of nearby pixels . Commonly used to generate text with smooth looking curves.

  Aspect Ratio : The comparison of an image or screen's height to its width.

  Blue Screening : See Chroma Keying.

  BNC Connector : A twist-lock cable connector used commonly on video equipment such as video cameras.

  Buffer : Generally, a RAM based device that temporarily holds computer data. Because of the very fast speed of RAM, these buffers can increase efficiency for time insistant processes such as digital video .

  Character Generator : Hardware or software that creates text for use in video. Generally, hardware devices are referred to as character generators, while software applications are often called video titlers.

  Chroma Keying : A real time  technique used to overlay one video signal on another, by allowing the front image to be transparent in certain areas (the key). One common use is by television weather news programs to place a reporter in front of a computer generated weather display. Also referred to as color keying and blue screening.

  Chrominance : The part of a color video signal that represents the saturation  and hue  of a specific point in an image. The lower the chrominance level is the weaker the color. Black and white video does not contain chrominance information.

  Clipping (Audio) : When recording audio, if an input signal is louder than can be properly reproduced by the hardware, the sound level will be cut off at its maximum. This process often causes distortion in the sound, so it is recommended that the input signal level be reduced in order to avoid this.

  Clipping (Video) : With video signals, clipping refers to the process of recording a reduced image size by ignoring parts of the source image. Also referred to as cropping.

  Codec : Refers to hardware or software used to encode and/or decode a signal or data file.

Color Keying : See Chroma Keying .

  Component Video : Refers to video signals where the components (luminance , chrominance  and synchronization ) are kept separate in order to achieve maximum video quality. There are several forms, including RGB  , S-Video , Y/C and YUV .

  Composite Sync : A synchronization  signal where horizontal and vertical signals are combined.

Composite Video : See CVBS .

  Compositing : The process of merging two or more images into one.

  Compression : The technique of processing data to reduce storage space and, as a result, improve datarate .

  Control-L / Control-M / Control-S: Special edit control  systems designed for communication between two video systems, allowing control of fast forward, rewind, pause, play, and other related functions. The different protocols are used by different manufacturers to perform similar functions, but are not compatible.

Cropping : See Clipping (Video) .

  CVBS : Composite Video Burst Signal. A type of video signal where luminance  and chrominance   signals are combined. Designed to be compatible with the black and white video signal. Generally uses an RCA type connector. Also referred to as composite video.

  Datarate : The amount of data that can be transferred in one second. The higher the datarate the better the video output can be. On the Amiga, a video card's datarate is restricted because of limitations imposed by the zorro  slots.

  Digital Video : A video signal where a limited number of steps is used to describe levels (colors).

  Digitization : The process of converting analog video or audio signals to digital data.

  DSP : Digital Signal Processor. Hardware specifically designed to compute floating point math at very high speeds. Among other things, DSP hardware can be used to do real time  compression  and decompression of video/audio signals.

  Dynamic Range : An image processing function used to force an image's color palette to fit within a defined range. Also, see Hot Signal .

  Edit Control : Communication connections on video hardware which allow device control of editing functions. Also, see Control-L .

  EDL : Edit Decision List. A manual or computer generated list of locations in video detailing scene changes, transitions  and other points of interest; used in the editing process.

  Field : One frame  of video consists of two interlaced  fields. For NTSC  video, each field is drawn in 1/60th of a second. Since the human eye has a persistence of about 1/50th of a second, the two fields seem to be displayed simultaneously. Also, see Flicker .

  Firewire : A high speed communication protocol designed for transfer between digital video  hardware such as cameras, editing systems and computers.

  Flicker : If a video display does not have a fast enough update rate, it will be perceived by the human eye as blinking or flickering. This is commonly experienced by Amiga users when viewing an interlaced  screenmode (such as 640x400) on a non-interlaced  monitor such as the Amiga 1080/1084 monitors.

  FPS : Frames Per Second. The number of images displayed during a period of one second.

  Frame : Motion video is made up of a series of still images, called frames, that change rapidly. For PAL  video, frames are displayed every 1/25th of a second. NTSC  video is updated every 1/30th of a second.

  Frame Buffer : Generally, a RAM based device that temporarily holds one or more frames  of image data. Also, see Buffer .

  Frame Grabber : A hardware device that can digitize  one or more frames  of video in real time . Also, see Video Digitizer .

  Frame Synchronizer : A hardware device that synchronizes two or more video timing signals. One input signal is used as the sync reference and other video signals are synchronized to it by slightly delaying them. Also, see Genlock  , TBC .

  Genlock : GENerator LOCKing. A hardware device that provides synchronization signals, to be used as timing for other connected devices, by generating a signal in sync with an input signal. Genlocking is commonly used to combine graphics from a computer with the video signal from another video source such as a video camera. Also, see Frame Synchronizer  , TBC .

  Hertz : A unit of frequency equivalent to one cycle per second.

  Hi-8 : An enhanced version of the 8mm video tape format. A higher density tape allows for improved luminance  which results in sharper image quality and a horizontal resolution  of 400 lines (compared to 240).

  Horizontal Resolution : A measurement of detail, rated in scan  lines. The greater the number of lines, the higher the resolution and the better the picture quality.

  Horizontal Sync : The part of the composite video signal that synchronizes the display so that images will start at the same horizontal position during scanning .

  Hot Signal : When a video signal exceeds the limitations of a display, color bleeding and oversaturation can occur. This is referred to as a hot signal. Computer graphics are able to display a wider range of color than video. It is important to keep this in mind when performing image processing functions destined for video. It is often necessary to perform a dynamic range  function, or similar, to limit the color range.

  Hue : The shade of a color.

  Interlaced : A scanning  method that displays alternating lines, first odd and then even. 1,3,5... 2,4,6... Also, see Field .

  JPEG : Joint Photographic Experts Group. JPEG is a lossy  image compression  method for single images. It works on the principal that some color information is beyond the limits of human vision and can therefore be removed. The compression ratio is adjustable from 1 (maximum compression, minimum image quality) to 100 (minimum compression, maximum image quality). It is important to note that not all software follows the JFIF Q-table standards for ratios, therefore a level of 60 in one program may not be equivalent in another program.

  KHz : Kilohertz. One thousand hertz  (cycles per second).

LANC : See Control-L  .

  Linear Editing : A process of editing using a medium, such as tape, that must be accessed in a sequential order. Example: Recording from one VCR  to another, using fast forward and record/pause to perform searching and record functions.

  Lossless : A compression  method that does not discard data is often called lossless. These methods are often preferred because they accurately represent the original data. GIF is an example of a lossless image compression.

  Lossy : A compression  method that discards data is often called lossy. These methods are not always preferred because they cause degradation in the quality of the data. JPEG  and MPEG  are examples of lossy compressions.

  LTC : Longitudinal Time Code. A system of time code  where information is recorded as an audio signal, generally, on an audio track of a video deck. Because the system is based in audio, tracking is only possible while a tape deck is in play mode. Generally, LTC is accurate to a single frame , in the form HH:MM:SS:FF (hours:minutes:seconds:frames).

  Luminance : The brightness information contained within a video signal.

  MHz : Megahertz. One million hertz  (cycles per second).

  Motion-JPEG : Not specifically a compression  method, but rather a method of storing images compressed using JPEG . Unlike, MPEG , each digital frame is stored as a separate file. This has the advantage that editing functions, such as re-ordering and deleting, are very quick. But, it has the disadvantage of requiring more storage space.

  MPEG : A lossy  image compression  method for a series of images (movies) based on the JPEG   standard. The advantage of this method, in comparison to Motion-JPEG , is that it requires less harddisk space. However, editing functions are much slower because the entire MPEG file has to be re-written every time changes are made. MPEG-1 specifies a resolution  of 352 x 240 played at 30 frames  per second. MPEG-2 specifies 720 x 480 at 60 fields  per second.

  Non-Interlaced : A scanning  method that displays lines in sequential order. 1,2,3,4,5,6...

  Nonlinear Editing : The process of editing using a medium, such as harddisk, that can be accessed in a random order. Generally, a very fast system with nearly instantaneous recall or indexing. Often abbreviated as NLE.

  NTSC : National Television Standards Committee. Video is displayed with 525 lines per frame  at a rate of 30 FPS . It is the standard used in North America, Japan, etc.

  PAL : Phase Alternation Line. The video standard used in most European Countries. Video is displayed with 625 lines per frame  at a rate of 25 FPS .

  Pixel : PIcture ELement. The dots of light that make up a computer display. The smallest unit of display information.

  Post-Roll : Extra video at the end of a video clip that is used for making scene transitions .

  Pre-Roll : Extra video at the beginning of a video clip that is used for scene transitions  and synchronization purposes.

  Real Time : Operation at the speed in which something occurs naturally.

  Resolution : The number of pixels  or dots that can be displayed horizontally and vertically on a monitor. Generally, the higher the resolution the better the quality.

  RPN : Reverse Polish Notation. In digital video  editing, it provides a method for processing multiple simultaneous transitions  and effects. Based on a concept of data and function stacks . Commonly used with calculators, where the RPN equivalent of "1 + 2" is "1 2 +".

  RGB : Red Green Blue . A type of video signal, used mostly for computer displays, where color is defined as percentages of red, green and blue.

  RS-232 / RS-422 : Serial communication interfaces used in video to control VCRs  and other editing equipment.

  Sample : Often used to refer to a file that contains digitized  audio data. However, this is a very common misuse of the word. A sample is a single digital value which represents a waveform amplitude from a single point in time. A group of samples, taken over a period of time, is called a sound or waveform (file).

  Saturation : The amount in which a color is absent of white light, where a 100% saturated color contains no white light. It is the property of color that makes, for example, pink and red different.

  Scanning : The process of displaying an image on a monitor by moving an electron beam from point to point, row to row; starting at the top and moving down to the bottom.

  Scene : A grouping of one or more video frames .

  SECAM : SEquential Coluleur A'Memorie. The television broadcast standard for various Eastern European countries. Like PAL , it displays at 25 FPS ; but with a higher horizontal resolution  of 819 lines.

  SMPTE : Society of Motion Picture and Television Engineers. An organization of technical experts who help to develop standards related to the video industry.

  Stack : Used with RPN  processing. A stack is a pile where elements are always added and taken from the bottom.

  Steady Shot : A system designed to improve hand-held camera video recording by compensating for camera-shake.

  S-VHS : Super VHS. An enhanced version of the VHS  tape format. A higher density tape allows for improved luminance  which results in sharper image quality and a horizontal resolution  of 400 lines.

  S-Video : A type of video signal, where luminance  (Y) and chrominance  (C) signals are kept separate, providing a higher quality signal than CVBS . Usually uses a multi-pin DIN type connector. Also referred to as Y/C.

  SYNC : Synchronous. Signals used to synchronize the horizontal and vertical scanning  of video.

  SYNC Generator : A hardware device that generates horizontal and vertical synchronization signals.

  TBC : Time Base Corrector. A hardware device that corrects errors in a video signal's timing information by generating a new time base and re-synchronizing the bad signal to it. VCRs  inherently have unstable timing and tape jittering problems which can cause problems when used with other video hardware. A TBC can be used to correct these errors. Also, see Frame Synchronizer , Genlock .

  Thermal Recalibration : When a harddisk heats up, its platters expand in size. As a result of this, a harddisk has to compensate for changes in data position by performing a thermal recalibration function. This can cause interruptions in data flow which would delay video output. This problem is commonly solved by using a data buffering  system.

  Time Code : A system used to accurately track positioning on video tape, where every frame can be individually identified. There are three main time code systems used in video: VITC , LTC  and RC.

  Transition : An effect applied to video to progress from one scene  into the next. Common transition effects include: wipes, dissolves, fades, page turns, shifts and rolls. Additionally, digital video  editing provides much more complex transition effects such as: bounce, melt, swirl and liquid.

  VCR : Video Cassette Recorder. Consumer level video recording device.

  Vertical Sync : The part of the composite video signal that indicates to the scanning  process when to move from the bottom of a frame  to the top again.

  VHS : Video Home System. A consumer level video format using half-inch magnetic tape, with a horizontal resolution  of 240 lines.

  Video Digitizer : Similar to a frame grabber  but requires longer than 1/30th of a second to digitize  a complete frame  and therefore can not be used for motion video. Among the more popular Amiga video digitizers is NewTek's Digi-View.

Video Titler : See Character Generator .

  VITC : Vertical Interval Time Code. A system of time code  that is embedded into a video signal. Its main advantage over LTC  is that tracking information is available as long as a video signal is present, even when the video deck is in pause mode. Accurate to a single field , in the form HH:MM:SS:FF:F (hours:minutes:seconds:frames:fields).

  VTR : Video Tape Recorder. Professional level video recording device.

Y/C : See S-Video  .

  YUV Component : A professional video format that uses three separated signals, one for luminance  and two for chrominance . This results in a picture quality that is higher than CVBS  and S-Video .

  YUV 4:2:2 : The current standard for storage of video on non-linear  digital editing systems. It represents the bits used for each of the three components, four for luminance  and two for each chrominance  signal. Also, see YUV Component .

  Zorro II/III : Amiga expansion slots. Zorro III, because of its 32-bit design improvements, provides a much faster datarate  and therefore is preferred over Zorro II for use with video editing systems.

Updated on Fri Mar 8 20:37:57 EST 2002