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Three cables, each with RCA plugs at both ends, are often used to carry analog component video

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 (NTSC, PAL or SECAM) in which all the video information is combined into a single line-level signal. Like composite, component-video cables do not carry audio and are often paired with audio cables.

When used without any other qualifications the term component video generally refers to analog YPbPr component video with sync on luma.

Contents

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. 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. A signal separated in this way is called "component video". S-Video, RGB and YPbPr 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[1], and new high definition TVs support the use of component video up to their native resolution.

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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 video (DVI) 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 for consumer use, although RGB was used extensively in commercial, professional and high-end installations.

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 (using pin 17 [gnd] and 19 [out] or 20 [in]). 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 (H) and white (V),[2] or yellow (H) and black (V), or gray (H) and black (V).[3]

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. Like devices that use composite video or S-video, 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.

YPbPr analog component video

Component video out

Further types of component analog video signals do not use R, G, and B components but rather a colorless component, termed luma, combined with one or more color-carrying components, termed chroma, that give only color information. Both the S-Video component video output (two separate signals) and the YPbPr 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 YPbPr 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", "Y/R-Y/B-Y" and Y, B-Y, R-Y. This is inaccurate since YUV, YPbPr, and Y B-Y R-Y differ in their scale factors.[4]

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.

Connectors used

S-Video analog component video

S-Video (S for separated) is sometimes considered a type of component video signal (transferring YUV when used for PAL video and YIQ when used for NTSC video), because the luma (Y) and chroma (UV or IQ) signals are transmitted on separate wires. However, it is also the poorest quality-wise, being far surpassed by the more complex component video schemes (like RGB). S-Video is not being used for high definition standards because the carrier frequency of the color 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, now EIA-343A)

Component versus composite

A possible source of confusion is that the word component differs from composite (an older, more widely-known video format) by just a few letters.[5]

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 incorrectly 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 YPbPr and composite video, with a software or hardware switch to determine which signal is generated. Hence, a common complaint is that the component video signals are very green, with very dark reds and blues. This is simply because the system menu has not been changed from AV (composite) to RGB (component).

References

  1. ^ 1080p over component video standard proposed to the CEA
  2. ^ Audio/Video Overview - types of signals
  3. ^ How to Use the 9A65 Component to RGB Video Converter
  4. ^ Poynton, Charles (November 28, 2006). "Color FAQ- Frequently Asked Questions about Color". http://www.poynton.com/ColorFAQ.html. Retrieved 2009-06-28.  
  5. ^ "The DV Show Question and Answer Database". January 1, 2007. http://www.thedvshow.com/faq-pro/index.php?action=article&cat_id=004&id=470. Retrieved 2008-06-22.  

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