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Component video is a video signal that has been split into two or more
components. In popular use, it refers to a type of analog video information that
is transmitted or stored as three separate signals. Component video can be
contrasted with composite video (such as NTSC or PAL) in which all the video
information is combined into a single line level signal. Component video cables
do not carry audio.
Analog component video
Reproducing a video signal on a display device (for example, a CRT) is a
straightforward process complicated by the multitude of signal sources.
LaserDisc, DVD, VHS, computers and video game consoles all store, process and
transmit video signals using different methods, and often each will provide more
than one signal option. One way of maintaining signal clarity is by separating
the components of a video signal so that they do not interfere with each other.
When a signal is separated this way it is called 'component video'. S-Video, RGB
and Y'PbPr signals comprise two or more separate signals: hence, all are
'component video' signals. For most consumer-level applications, analog
component video is used. Digital component video is slowly becoming popular in
both computer and home-theatre applications. Component video is capable of
carrying signals such as 480i, 480p, 576i, 576p, 720p, 1080i and 1080p.
RGB analog component video
The various RGB (Red, Green, Blue) analog component video standards (e.g., RGBS,
RGBHV, RG&SB) use no compression and impose no real limit on color depth or
resolution, but require large bandwidth to carry the signal and contain much
redundant data since each channel typically includes the same black and white
image. Most modern computers offer this signal via the VGA port. Many
televisions, especially in Europe, utilize RGB via the SCART connector. All
arcade games, excepting early vector and black and white games, use RGB
monitors.
Analog RGB is slowly falling out of favor as computers obtain better clarity
using Digital (DVI) video and home theater moves towards HDMI. Analog RGB has
been largely ignored, despite its quality and suitability, as it cannot easily
be made to support Digital Rights Management. RGB was never popular in North
America for consumer electronics, as S-Video was considered sufficient.
RGB requires an additional signal for synchronizing the video display. Several
methods are used:
* composite sync, where the horizontal and vertical signals are mixed together
on a separate wire (the S in RGBS)
* separate sync, where the horizontal and vertical are each on their own wire
(the H and V in RGBHV)
* sync on green, where a composite sync signal is overlaid on the green wire
(SoG or RGsB).
Composite sync is common in the European SCART connection scheme. Sometimes a
full composite video signal may also serve as the sync signal, though often
computer monitors will be unable to handle the extra video data. A full
composite sync video signal requires four wires – Red, Green, Blue, Sync. If
separate cables are used, the sync cable is usually colored white (or yellow, as
is the standard for composite video).
Separate sync is most common with VGA, used worldwide for analog computer
monitors. This is sometimes known as RGBHV, as the horizontal and vertical
synchronization pulses are sent in separate channels. This mode requires five
conductors. If separate cables are used, the sync lines are usually yellow (V)
and white (H), or yellow (V) and black (H), or black (V) and gray (H).[1]
Sync on Green (SoG) is the least common, and while some VGA monitors support it,
most do not. Sony is a big proponent of SoG, and most of their monitors (and
their PlayStation 2 video game console) use it. SoG devices require additional
circuitry to remove the sync signal from the green line. A monitor that is not
equipped to handle SoG will display an image with an extreme green tint, if any
image at all, when given a SoG input.
Y'PbPr analog component video
Further types of component analogue video signals do not use R,G,B components
but rather a colorless component, termed luma, combined with one or more
color-carrying components, termed chroma, that give only color information. This
overcomes the problem of data redundancy that plagues RGB signals, since there
is only one black and white image carried, instead of three. Both the S-Video
component video output (two separate signals) and the Y'PbPr component video
output (three separate signals) seen on DVD players are examples of this method.
Converting video into luma and chroma allows for chroma subsampling, a method
used by JPEG images and DVD players to reduce the storage requirements for
images and video. The Y'PbPr scheme is usually what is meant when people talk of
component video today. Many consumer DVD players, high-definition displays,
video projectors and the like, use this form of color coding.
These connections are commonly and mistakenly labeled with terms like "YUV" and
Y, B-Y, R-Y. This is inaccurate since Y'UV, Y'PbPr, and Y' B'-Y' R'-Y' differ in
their scale factors.[2]
In component video systems, additional synchronization signals may need to be
sent along with the images. The synchronization signals are commonly transmitted
on one or two separate wires, or embedded in the blanking period of one or all
of the components. In computing, the common standard is for two extra wires to
carry the horizontal and vertical components ('separate syncs'), whereas in
video applications it is more usual to embed the sync signal in the Y' component
('sync on luma').
When used for connecting a video source to a video display where both support
4:3 and 16:9 display formats, the PAL television standard provides for signaling
pulses that will automatically switch the display from one format to the other.
However Y'PbPr does not support this operation.
Connectors used
* D-Terminal: Used mostly on Japanese electronics.
* Three BNC (professional) or RCA connectors (consumer): Typically colored red
(Pr), green (Y), and blue (Pb).
* SCART used in Europe.
S-Video analog component video
S-Video (S for Separate) is another type of component video signal (transferring
Y'UV when used for PAL video and Y'IQ when used for NTSC video), because the
luma (Y') and chroma (UV or IQ) signals are transmitted on separate wires. This
connection type is not being used for high definition standards as the carrier
frequency of the colour signal modulation would have to be adjusted.
International standards
Examples of international component video standards are:
* RS-170 RGB (525 lines, based on NTSC timings, now EIA/TIA-343)
* RS-343 RGB (525, 625 or 875 lines)
* STANAG 3350 Analogue Video Standard (NATO military version of RS-343 RGB)
Confusions
Component video connectors are not unique in that the same connectors are used
for several different standards; hence, making a component video connection
often does not lead to a satisfactory video signal being transferred. The
settings on many DVD players and TVs may need to be set to indicate the type of
input/output being used, and if set wrong the image may not be properly
displayed. Progressive scan, for example, is often not enabled by default, even
when component video output is selected.
Modern game systems (such as the PlayStation 3, Xbox 360, and Wii) use the same
connector pins for both RGB and component video, with a software or hardware
switch to determine which signal is generated. Hence, a common complaint,
especially with the PlayStation 2, is that the RGB signals are very green, with
very dark reds and blues. This is because the system menu has not been changed
from Component to RGB. This problem also occurs when trying to play back DVDs on
the PS2 using the RGB-output.
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