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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.
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.
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.
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.
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.
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.
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.
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.
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.
Drop Frame
Time Code
An SMPTE Time
Code (TC) option that allows indicated TC to agree with clock time.
The color frame rate for color TV is actually 29.97 frames per
second, not 30, so that over a 60 minute period a TC reader would
count 108 frames (3.6 seconds) short. To correct this situation, at
the beginning of each minute frames 0 and 1 are "dropped"
so that the frame count starts at 2. This would result in 120 frames
added in an hour, 12 more than needed. By negating this correction at
the beginning of every 10th minute, time code is forced to agree with
clock time.
Dropout
A loss of
picture information that may appear as a short white flash and
include one or more picture scan lines. Dropouts are caused by minute
imperfections in the surface of the tape stock or by dust particles
attracted to the tape by static electricity.
Dropout
Compensator (DOC)
An electronic
device in a VCR or VTR that detects the presence of a dropout and
replaces it with information from the preceding line, thereby
covering up the dropout.
Dub
In television,
a copy of a videotape. dub is more commonly used than dupe (short for
duplicate), which generally applies to film copies.
Edit
Decision List (EDL)
A structured
compilation of time code information defining each edit in a sequence.
The EDL consists of pertinent information such as time code edit
points, notes, and switcher data.
Field
One-half of a
NTSC television frame. A field contains 262.5 lines and has duration
of 1/60th of a second. The odd numbered scanning lines are known as
field 1, the even numbered as field 2. When these fields are combined
by interlacing, a 525 line frame results.
Frame
A standard
unit of video information containing one complete image. The NTSC
system standard in the United States and many other countries
transmits nominal 30 frames per second. A frame is made up of two
television fields, one odd and one even. Each field is made up o
262.5 lines of information. When interlaced the two fields generate a
video frame of 525 lines.
Helical Scan
VTR or VCR
recording format that wraps the tape around the video scanner in a
helix pattern.
Hue
A specific
color wavelength in the visible light spectrum, an attribute of color
perception. Flesh tones, for example, may be changed by adjusting the
hue control (sometimes marked color phase) on a television receiver
or monitor.
Interlace
The combining
of two sequential television fields that make up a complete frame in
the NTSC system. Field 1 contains the odd numbered scan lines, field
2 the even numbered line.
Luminance
The intensity
of light: specifically, the monochrome component or the brightness
potion of a video image. The symbol "Y" is used to identify
the luminance signal in composite and component color systems.
Noise, Video
A random
signal generated by most electronic equipment, which is present
throughout the video signal spectrum. Video noise is somewhat
analogous to film grain.
Non-Drop
Frame Time Code
A time-based
reference system for video and audio that was developed and
standardized by the SMPTE. The system assigns each frame a distinct
eight-digit number that is composed of hours, minutes, seconds, and frames.
Because of the nature of the NTSC color television system, non-drop
frame time code does not agree with clock time.
Safe Title
and Safe Action Areas
Geometric
boundaries within the television viewing area used as a guide to
insure the correct placement of graphics, titles of other types of
art work so as not to lose the desired action or title information as
seen on a television receiver.
Saturation
The intensity
of the color in a video picture. The greater the color (chroma)
saturation, the more intense the color. The amount of color
saturation may be seen on a vectorscope.
SCH
(SubCarrier to Horizontal Phase)
Refers to the
timing relationship that must exist between the color burst and the
leading edge of sync to obtain clean color edits. The zero crossing
of SCH must be time coincident with leading edge of horizontal sync.
Sync
The pulses in
a video signal that provide a synchronizing reference for each frame
and scanning line of the picture.Sync, Editorial
Time Base Error
The horizontal
and/or vertical jitter inherent in most videotape recording
equipment. Broadcast standards require a horizontal line-to-line
timing accuracy of better than one part in thousands, which is
impossible to attain in a mechanical tape-scanning device. An
electronic automatic time delay device, known as a Time Base
Corrector (TBC) is necessary in all helical scan VTRs to compensate
for this inherent problem if the video is to be broadcast or
composited (dissolve, wipe, matte) in any way.
TBC (Time
Base Corrector)
An electronic
processing device connected to the output of a VCR or VTR that
removes or masks the jitter generated by unavoidable mechanical
inaccuracies in helical scan recorders. This is accomplished by
automatically delaying the video signal so that each line starts at
the proper time.
Time Code
Generator (TCG)
An electronic
clock that generates a digital serial code that can be recorded on an
audio track, which assigns to each video or audio frame a unique
identification number composed of eight digits.
Tracking
The process by
which the video head precisely follows the recorded video signal on
playback. Correct tracking assures a noise free reproduction of the
picture.
Vectorscope
An instrument
used to setup color encoders and to confirm the proper transmission
and/or recording of color signal. A CRT displays the color subcarrier
in a circular pattern. The graticule contains a pattern of measuring
boxes in positions based on the hue and chroma characteristics of the
color bar signal. The individual bars appear as bright dots which
should fall within the small boxes if the color signal has been
correctly encoded and has not been altered in transmission or
recording. The angular position of the color vector indicates the hue
(phase) of the color. The length of the vector is a measure of the
saturation. The color burst reference marker, a horizontal bar
situated at the 9 o’clock position on the graticule, is the
established reference with respect to the six colors positioned in
their respective boxes.
VITC
(Vertical Interval Time Code)
Time code that
is recorded on two lines of the vertical blanking period in the video
signal. Unlike time code recorded on a longitudinal linear audio
channel, VITC time code is scanned by the video head even when in
still frame. This time code then is converted to a readable time code
that may be used to frame accurately, locate, and define edit points.
Waveform Monitor
A display
device that shows the electronic pattern of the video signal on the
face of a Cathode Ray Tube (CRT). Superimposed on the screen is
a scale vertically divided into 140 divisions, termed I.R.E. units.
The synchronizing pulses occupy the range between -40 and 0.
The video waveform starts at 0 with black at 7.5 and white at 100.
A WFM allows the operator to view the video signal and make the
appropriate adjustments as necessary to keep the video signal within
prescribed limits. It is also used to measure sync signal
parameters to be sure that they conform to accepted standards.
Common test signals such as color bars, multi-burst, staircase and
window can easily be evaluated to determine the performance of an
incoming source or the playback of a recorder.
Window Dub
A copy of
original videotape with the eight-digit time code displayed in a
rectangular area generally at the bottom of the screen. This window
area may be surrounded by a black box so that the time code numbers
stand out against a light background. The window dub is used only as
a viewing copy or may be used as a work copy tape to edit with since
the numbers once recorded in the picture cannot be removed. |
