C
- Cable equalization: The process
of altering the frequency response of a video amplifier to compensate
for high-frequency losses in coaxial cable.
- CAD: Computer-aided design.
This usually refers to a design of system that uses computer specialized
software.
- Candela [cd]. A unit for measuring
luminous intensity. One candela is approximately equal to the amount
of light energy generated by an ordinary candle. Since 1948 a more precise
definition of a candela has become: "the luminous intensity of
a black body heated up to a temperature at which platinum converges
from a liquid state to a solid".
- CATV: Community antenna television.
- C-band: A range of microwave
frequencies, 3.7~4.2 GHz, commonly used for satellite communications.
- CCD: Charge-coupled device.
The new age imaging device, replacing the old tubes. When first invented
in the 1970's, it was initially intended to be used as a memory device.
Most often used in cameras, but also in telecine, fax machines, scanners,
etc.
- CCD aperture: The proportion
of the total area of a CCD chip that is photosensitive.
- CCIR: Committee Consultatif
International des Radiocommunique or, in English, Consultative Committee
for International Radio, which is the European standardization body
that has set the standards for television in Europe. It was initially
monochrome; therefore, today the term CCIR is usually used to refer
to monochrome cameras that are used in PAL countries.
- CCIR 601: An international standard
(renamed ITU 601) for component digital television that was derived
from the SMPTE RP1 25 and EBU 3246E standards. ITU 601 defines the sampling
systems, matrix values and filter characteristics for Y, Cr, Cb and
RGB component digital television. It establishes a 4:2:2 sampling scheme
at 13.5 MHz for the luminance channel and 6.75 MHz for the chrominance
channels with eight-bit digitizing for each channel. These sample frequencies
were chosen because they work for both 525-line 60 Hz and 625-line 50
Hz component video systems. The term 4:2:2 refers to the ration of the
number of luminance channel samples to the number of chrominance channel
samples; for every four luminance samples, the chrominance channels
are each sampled twice. The D1 digital videotape format conforms to
ITU 601.
- CCIR656: The international standard
(renamed ITU 601) defining the electrical and mechanical interfaces
for digital television equipment operating according to the ITU 601
standard. ITU 656 defines both the parallel and serial connector pinouts,
as well as the blanking, sync and multiplexing schemes used in both
parallel and serial interfaces.
- CCTV: Close circuit television.
A television system intended for only a limited number of viewers, as
opposed to broadcast TV.
- CCTV camera: A unit containing
an imaging device that produces a video signal in the basic bandwidth.
- CCTV installation: A CCTV system,
or an associated group of systems, together with all necessary hardware,
auxiliary lighting, etc., located at the protected site.
- CCTV system: An arrangement
comprising of a camera and lens with all ancillary equipment required
for the surveillance of a specific protected area.
- CCVE: Stands for closed circuit
video equipment. An alternative acronym from CCTV.
- CD: Compact disc. A standard
of media as proposed by Philips and Sony, where music and data are stored
in digital format.
- CD-ROM: Compact disc read only
memory. The total capacity of a CD-ROM when storing data is 640 MB.
- CDS: Correlated double sampling.
A technique used in the design of some CCD cameras that reduces the
video signal noise generated by the chip.
- CFA: Color filter array. A set
of optical pixel filters used in single-chip color CCD cameras to produce
the color components of a video signal.
- Chip: An integrated circuit
in which all the components are micro-fabricated on a tiny piece of
silicon or similar material.
- Chroma crawl: An artifact of
encoded video, also known as dot crawl or cross-luminance, occurs in
the video picture around the edges of highly saturated colors as a continuous
series of crawling dots and is a result of color information being confused
as luminance information by the decoder circuits.
- Chroma gain (chroma, color,
saturation): In video, the gain of an amplifier as it pertains to the
intensity if colors in the active picture.
- Chroma key (color key): A video
key effect in which one video signal is inserted in place of areas of
a particular color in another video signal.
- Chrominance: The color information
of a color video signal.
- Chrominance-to-luminance intermodulation
(crosstalk, cross-modulation): An undesirable change in luminance amplitude
caused by superimposition of some chrominance information on the luminance
signal. Appears in a TV picture as unwarranted brightness variations
caused by changes in color saturation levels.
- CIE: Commission Internationale
de l'Eclairage. This is the International Committee for Light, established
in 1965. It defines and recommends light units.
- Clamping (DC): The circuit or
process that restores the DC component of a signal. A video clamp circuit,
usually triggered by horizontal synchronizing pulses, re-establishes
a fixed DC reference level for the video signal. A major benefit of
a clamp is the removal of low-frequency interference, especially power
line hum.
- Cladding: The outer part of
a fiber optics cable, which is also a fiber but with a smaller material
density than the center core. It enables a total reflection effect so
that the light transmitted through the internal core stays inside.
- Clipping level: An electronic
limit to avoid overdriving the video portion of the television signal.
- C-mount: The first standard
for CCTV lens screw mounting. It is defined with the thread if 1"
(2.54mm) in diameter and 32 threads/inch, and the back flange-to-CCD
distance of 17.526mm (0.69"). The C-mount description applies to
both lenses and cameras. C-mount lenses can be put on both C-mount and
CS-mount cameras; only in the latter case an adaptor is required.
- CMYK: A color encoding system
used by printers in which colors are expressed by the "subtractive
primaries" (cyan, magenta and yellow) plus black (called K). The
black layer is added to give increased contrast and range on printing
presses.
- Coaxial cable: The most common
type of cable used for copper transmission of video signals. It has
a coaxial cross-section, where the center core is the signal conductor,
while the outer shield protects it from external electromagnetic interference.
- CODEC: Code/Decode. An encoder
plus a decoder is an electronic device that compresses and decompresses
digital signals. CODECs usually perform A/D and D/A conversion.
- Color bars: A pattern generated
by a video test generator, consisting of eight equal width color bars.
Colors are white (75%), black (7.5% setup level), 75% saturated pure
colors red, green and blue, and 75% saturated hues of yellow, cyan and
magenta (mixtures of 2 colors in 1:1 ratio without third color).
- Color carrier: The sub-frequency
in a color video signal (4.43 MHz for PAL) that is modulated with the
color information. The color carrier frequency is chosen so its spectrum
interleaves with the luminance spectrum with minimum interference.
- Color difference signal: A video
color signal created by subtracting luminance and/or color information
from one of the primary color signals (red, green or blue). In the Beta
cam color difference format, for example, the luminance (Y) and color
difference components (R-Y and B-Y) are derived as follows:
Y = 0.3 Red + 0.59 Green + 0.11 Blue
R-Y = 0.7 Red - 0.59 Green - 0.11 Blue
B-Y = 0.89 Blue - 0.59 Green - 0.3 Red
The G-V color difference signal is not created because it can be reconstructed
from the other three signals. Other color difference conventions include
SMPTE, EBU-N1 0 and MII. Color difference signals should not be referred
to as component video signals. That term is resaved for the RGB color
components. In informal usage, the term "component video"
is often used to mean color difference signals.
- Color field: In the NTSC system,
the color sub-carrier is phase-locked to the line so that on each consecutive
line, sub-carrier phase is changed 180 degrees with respect to the sync
pulses. In the PAL system, color sub carrier phase moves 90 degrees
every frame. In NTSC this creates four different filed types, while
in PAL there are eight. In order to make clean edits, alignment of color
field sequences from different sources is crucial.
- Color frame: In color television,
four (NTSC) or eight (PAL) properly sequenced color fields compose one
color frame.
- Color phase: The timing relationship
in a video signal that is measured in degrees and keeps the hue of a
color signal correct.
- Color sub-carrier: The 3.58
MHz signal that carries color information. This signal is superimposed
on the luminance level. Amplitude of the color sub-carrier represents
saturation and phase angle represents hue.
- Color temperature: Indicates
the hue of the color. It is derived from photography where the spectrum
of colors is based upon a comparison of the hues produced when a black
body (as in physics) is heated from red through yellow to blue, which
is the hottest. Color temperature measurements are expressed in Kelvin.
- Comb filter: An electrical filter
circuit that passes a series of frequencies and rejects the frequencies
in between, producing a frequency response similar to the teeth of a
comb. Used on encoded video to select the chrominance signal and reject
the luminance signal, thereby reducing cross-chrominance artifacts or
conversely, to select the luminance signal and reject the chrominance
signal, thereby reducing cross-luminance artifacts. Introduced in the
S-VHS concept for a better luminance resolution.
- Composite Sync: A signal consisting
of horizontal sync pulses, vertical sync pulses and equalizing pulses
only, with no-signal reference level.
- Composite video signal: A signal
in which the luminance and chrominance information has been combined
using one of the coding standards NTSC, PAL, SECAM, etc.
- Concave lens: A lens that has
negative focal length; i.e., the focus is virtual and it reduces the
objects.
- Contrast: A common term used
in reference to the video picture dynamic range, i.e., the difference
between the darkest and the brightest parts of an image.
- Convex lens: A convex lens has
a positive focal length, i.e., the focus is real. It is usually called
magnifying glass, since it magnifies the objects.
- CPU: Central processing unit.
A common term used in computers.
- CRO. Cathode ray oscilloscope
(see Oscilloscope)
- Crosstalk: A type of interference
of undesired transmission of signals from one circuit into another circuit
in the same system. Usually caused by unintentional capacitance (AC
coupling).
- CS-Mount: A newer standard for
lens mounting. It uses the same physical thread as the C-mount, but
the back flange-to-CCD distance is reduced to 12.5mm in order to have
the lenses made smaller, more compact and less expensive. CS-mount lenses
can only be used on CS-mount cameras.
- CS-to-C-mount adaptor: An adaptor
used to convert a CS-mount camera to C-mount to accommodate a C-mount
lens. It looks like a ring 5 mm thick, with a male tread on one side
and a female on the other, with 1" diameter and 32 threads/inch.
It usually comes packaged with the newer type (CS-mount) of cameras.
- CVBS: Composite video bar signal
in broadcast television this refers to the video signal, including the
color information and syncs.
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