Glossary of Video Terms and Acronyms - Isotest

Video Terms and Acronyms
Glossary
change may be caused by clipping of high-amplitude chrominance peaks,
quadrature distortion or crosstalk. The modulated pedestal is used to test
for this distortion. Distortions can be expressed as: IRE with the pedestal
level normalized to 50 IRE, as a percentage of the pedestal level, as a percentage
of the measured white bar amplitude, as a percentage of 714 mV.
These definitions will yield different results under some conditions so it is
very important to standardize on a single method of making intermodulation
measurements. Picture effects include unwarranted brightness variations
due to color saturation changes affecting the luminance.
Chromium Dioxide (CrO2 ) – A modern magnetic particle oxide of the high
energy type used in magnetic recording tape. Chromium dioxide is a highly
acicular particle with the crystal structure of rutile. Tapes made of CrO2 exhibit a coercivity of 425 to 475 oersteds.
CI – Common Interface.
CIE (Commission Internationale de l’Eclairage) – French acronym for
the International Illumination Commission. An international standardization
organization that created the chromaticity diagrams (color charts) used to
define the colorimetry of all television systems. The CIE is concerned with
methods of measurement plus recommended practices and standards concerning
the properties and applications of light.
CIE 1931 Standard Colorimetric System (XYZ) – A system for determining
the tristimulus values of any spectral power distribution using the
set of reference color stimuli X, Y, Z, and the three CIE color matching
functions x(lambda), y(lambda), z(lambda), adopted by the CIE in 1931.
CIELab Color Space – Three-dimensional, approximately uniform color
space produced by plotting in rectangular coordinates L*, a*, b* quantities
defined by the following equations. X, Y, Z describe the color stimulus considered,
and Xn, Yn, Zn describe a specified white achromatic stimulus
(i.e., white reference). Equal distances in the color space represent approximately
equal color differences.
L* = 116 (Y/Yn)^(1/3) – 16 Y/Yn
a* = 500 [(X/Xn^(1/3) – (Y/Yn)^(1/3)] X/Xn > 0.008 856 ] b* = 200 {(Y/Yn)^(1/3) – (Z/Zn)^(1/3)] Z/Zn
CIELuv Color Space – Three-dimensional, approximately uniform color
space produced by plotting in rectangular coordinated L*, u*, v* quantities
defined by the following equations. Y, u', v' describe the color stimulus
considered, and Yn, u'n, v'n describe a specified white achromatic stimulus
(white reference). The coordinates of the associated chromaticity diagram
are u' and v'. L* is the approximate correlation of lightness, u* and v* are
used to calculate an approximate correlate of chroma. Equal distances in
the color space represent approximately equal color differences.
L* = 116 (Y/Yn)^(1/3) – 16 Y/Yn > 0.008 856
u* = 13 L * (u' – u'n)
v* = 13 L * (v' – v'n)
CIF – See Common Image Format, Common Interchange Format, Common
Interface Format, or Common Intermediate Format.
Cinching – Longitudinal slippage between the layers of tape in a tape
pack when the roll is accelerated or decelerated.
CinemaScope – The first modern widescreen movie format, achieving a
2.35:1 aspect ratio through the use of a 2:1 anamorphic squeeze.
30 www.tektronix.com/video_audio
CinePak – CinePak is a compression scheme dedicated to PC environments,
based on a vector quantization algorithm. CinePak is a highly asymmetrical
algorithm, i.e., the encoding takes much more processing power
than the decoding process. The CinePak algorithm is developed by Radius,
and is licensed by a range of companies. Both Microsoft Windows 95
and Apple’s QuickTime have built in CinePak, for instance.
CK – See Chroma Key.
Clamp – a) A device which functions during the horizontal blanking or
sync interval to fix the level of the picture signal at some predetermined
reference level at the beginning of each scanning line. b) Also known as a
DC-restoration circuit, or it can also refer to a switch used within the DCrestoration
circuit. When used in the context of DC restoration, it is usually
used as “clamping.” When used in its switch context, it is referred to as
just “clamp.”
Clamper – A device which functions during the horizontal blanking or sync
interval to fix the level of the picture signal at some predetermined reference
level at the beginning of each scanning line.
Clamping – a) The process that establishes a fixed level for the picture
signal at the beginning of each scanning line. b) The process whereby a
video signal is referenced or “clamped” to a DC level to prevent pumping
or bouncing under different picture levels. Without clamping, a dark picture
would bounce if a white object appeared. Changes in APL would cause
annoying pulsations in the video. Clamping is usually done at zero DC level
on the breezeway of the back porch of horizontal sync. This is the most
stable portion of a TV picture.
Clean Rooms – Rooms whose cleanliness is measured by the number of
particles of a given size per cubic foot of room volume. For example, a
class 100,000 clean room may have no more than 100,000 particles onehalf
micron or larger per cubic foot. Similarly, for class 10,000 and class
100 rooms. In addition, a class 10,000 room may have no more than 65
five-micron particles per cubic foot, while class 100,000 may have no
more than 700.¨
Clear – Set a circuit to a known state, usually zero.
Clear Channel – AM radio station allowed to dominate its frequency with
up to 50 kW of power; their signals are generally protected for distance of
up to 750 miles at night.
Click – To hold the mouse still, then press and immediately release a
mouse button.
Click and Drag – A computer term for the user operation of clicking on
an item and dragging it to a new location.
Cliff Effect – An RF characteristic that causes DTV reception to change
dramatically with a small change in power. At the fringes of reception, current
analog TV pictures degrade by becoming “snowy.” With DTV, relatively
small changes in received power in weak signal areas will cause the DTV
picture to change from perfect to nothing and hence the name, cliff effect.
Clip – a) A video file. b) In keying, the trigger point or range of a key
source signal at which the key or insert takes place. c) The control that
sets this action. to produce a key signal from a video signal, a clip control
on the keyer control panel is used to set a threshold level to which the
video signal is compared. d) In digital picture manipulators, a manual