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A and B Rolls
The process used to create optical effects, such as dissolves or wipes in film or videotape. The A roll contains the outgoing scene and the B roll contains the incoming scene. The point where the A and B scenes begin to overlap is the start of the effect. The length of the overlap is known as the duration of the effect. See Figure 10 on page 24.

Analog
See Analog vs. Digital Recording Methods on Page 54.

ASCII
American Standard Code for Information Interchange. A standard for data coding, particularly in computers. It is a list of encoded letters, numbers, characters, and other symbols similar to those on a standard typewriter keyboard. It is pronounced as "AS-KEY." topˆ

Auto Assembly
The computer assisted compilation of a series of edits. Information on each edit’s source, duration, and nature may be fed into the computer from punched paper tape or a floppy disk. Auto-assembly is the fastest method of editing videotape since all creative decisions have been made and previously entered into the computer for the auto assembly. topˆ

Black Level
The video signal level corresponding to black areas in a scene. For a composite signal, black is standardized at +7.5 units as viewed on a waveform monitor IRE scale. This elevated black level is often referred as "setup" and serves as a guard band between video and sync. For component video, black is at 0 units. See Figure 22. topˆ

Blanking
The process of turning off the electron scanning beam of a camera or picture tube so it will not be seen while it repositions itself for the next scan of a field or line. There are two forms of blanking pulses in a television signal. The horizontal (H) blanking pulse cuts off the beam during the retrace period from the right to left side of the picture. The vertical (V) pulse cuts off the beam as it moves from the bottom of the screen back to the top to start the scan of the next picture field. Blanking widths are chosen to provide adequate time for beam retrace in a practical TV set. Since the width and position of the blanking pulses (relative to sync) establish the heighth, width, and position of the picture as viewed on a monitor, their values must be carefully monitored. This is particularly important when switching between camera and/or VT sources to obviate shifts of the picture area. topˆ

Burst (Color)
A color reference signal included as part of the overall composite video signal. Eight to ten cycles of color sub-carrier (3.579545 MHz, often abbreviated as 3.58) are inserted before the start of every horizontal line. It can be seen just following the H sync pulse in the H blanking interval. It provides color-synchronizing information for the color decoding circuits in monitors, receivers and other TV equipment. These have "color killer" circuits that disable the color decoded if the burst is not present so that the signal is processed as monochrome. The burst must be precisely timed in relation to H sync. See SCH. See Figure 23. topˆ

Chrominance (Chroma)
The color information in a television picture. Seen on a waveform monitor as the color subcarrier riding on top of the luminance signal. Low chroma means that the color picture is pale looking or washed out. Excessive or high chroma means that the color is too intense and has a tendency to bleed into surrounding areas, contaminating nearby colors or in sever cases, causing video breakup. See Hue, Saturation. topˆ

Clipping
A form of video distortion. It is seen as a loss of detail in the black or white areas of the picture. It may be caused by excessive video levels that cannot be handled by the television system. To avoid these problems in transmission or recording situations where such overloads could cause serious problems in transmission or recording situations where such overloads could cause serious problems, controls are provided on cameras, proc amps, and recorders that allow an operator to constructively clip extraneous peaks. Example: A camera is viewing a scene that contains bright lights and/or specular reflections. The video operator would adjust the camera for appropriate skin tone levels and allow the extraneous super-white peaks to be clipped. See Compression. topˆ

Color Bars
An electronically generated standard set of colors used as a reference for proper equipment setup. Color bars include the three additive primary colors (red, green, and blue) and their complements (cyan, magenta, and yellow) displayed in vertical rows, plus gray and black. The bars appear left to right in order of decreasing luminance – yellow, cyan, green, magenta, red, and blue. Videotape machines, cameras, telecine chains, and monitors all use color bars as a reference for proper setup. The waveform can be examined on a waveform monitor or vectorscope to verify that the encoding process was proper and/or that it was not changed by any subsequent transmission or recording process. Color bars are readily available and easily interpreted and so have become a de-facto set standard. There are several variations of color bars. Full field bars show the color bars running the full height of the screen. EIA (Electronic Industries Association) bars assigns the bottom third of the pattern to the –I, Q, and black level set signals, which are useful for setup of camera encoders. SMPTE bars are the same as EIA, but insert another set of short color bars above the I and Q bars. These bars run in the reverse color order of the regular bars and are a convenient aid for the setup of color monitors. All versions allow the overall amplitude of the subcarrier (chrominance) to be set at 100% or 75% of the standard value. The 75% value is usually used for recording to avoid possible overload problems from highly saturated yellows and cyans. The amplitude of the gray bar can be set at 100% or 75% IRE units. See Figure 24. topˆ

Color Frame
The color subcarrier (SC) frequency is chosen to minimize its appearance in monochrome receivers. A side effect of this choice is that the SC phase is not contiguous between frames since the color frame sequence takes 2 frames to complete. If color disturbances are to be avoided, seen as horizontal picture shifts, edits should be made only between even numbered time code frames or between odd numbered frames. Editing systems automatically made these choices. topˆ

Component Video
A form of video, in which the luminance and chrominance signals are generated, transmitted and/or recorded on videotape as two independent signals, usually on individual video tracks. Unlike composite video, where the chrominance and luminance signals are combined as one signal; component video signals retain maximum bandwidth and avoid mutual interference through many generations of editing or duplication. topˆ

Composite Video
A video signal that combines luminance and chrominance by using one of several world wide electronic encoding methods, such as NTSC, PAL, or SECAM. Encoding a video signal reduces the bandwidth, and therefore the resolution, since a single channel is used to carry all the information. Current practice is to use composite video signals for most applications, although component video editing is gradually replacing composite editing. topˆ

Compression, Amplitude
The lack of gray scale separation in signal levels. A lack of detail in the white areas of the picture is called white compression and a lack of detail in the very dark areas is called black compression. However, controlled white compression is often introduced in camera signal processing to show detail in white areas that might otherwise have to be clipped. See Clipping. topˆ

Control Track
A guide pulse acting as an electronic sprocket hole recorded on the videotape. Control track pulses are used by servo systems to maintain a tape speed that allows precise playback head tracking. Control track pulses are recorded one per television frame and are used in lieu of time code by very basic editing systems to locate edit points and make edits. Missing control track signals may cause the video signal to break up or mistrack. This type of problem is analogous to that resulting from torn sprocket holes on film. topˆ

Cue Track
A secondary audio channel used to record time code or other non-program information. topˆ

 

 

 

 


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