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Like any technology, digital video comes complete with a plethora of standards, features, functions and buzz words; that can sometimes leave you a bit confused (especially when starting out). So, here is a glossary of Amiga and digital video related terms that should help clear up your mind a bit.
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%).
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.
Blue Screening: A post production technique used to overlay one image on another, by using a color background (commonly blue or green) as a mask to superimpose a second image. A very expensive and time consuming process using an optical printer; but, now more commonly processed using computer software. Similar to Chroma Keying and color keying.
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). ChromaKey produces a mask where each pixel is either off or on. Because of the sharpness along the edges, this effect may look very fake. Similar to 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.
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.
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.
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.
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 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.
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.
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).
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.
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.
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 +".
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).
Scene: A grouping of one or more video frames.
Stack: Used with RPN processing. A stack is a pile where elements are always added and taken from the bottom.
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.
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.
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.
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).
Y/C: See 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.