Component video


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

Component video is a video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) 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 that is used in analog television. 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 Cathode ray tube) (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 even 1080p (although Blu-Ray movies cannot be played at 1080p using component cables; the display would either switch to 1080i or 720p). Many new high definition TVs support the use of component video up to their native resolution.

RGB analog component video

A 15-pin VGA connector for a modern personal computer.
A 21-pin SCART connector.

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 DisplayPort or Digital Visual Interface (DVI) digital connections, while home theater moves towards High-Definition Multimedia Interface (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).
  • sync on red or sync on blue, where a composite sync signal is overlaid on either the red or blue wire

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),[1] or yellow (H) and black (V), or gray (H) and black (V).[2]

Sync on Green (SoG) is less 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.

Sync on red and sync on blue are even rarer than sync on green, and are typically used only in certain specialized equipment.

YPbPr analog component video

YPbPr component video out on a consumer electronics device.

Further types of component analog video signals do not use R, G, and B components but rather a colorless component, termed luma, which provides brightness information (as in black-and-white video). This combines 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 other video devices 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.[3]

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

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)
  • CEA-770.3 High Definition TV Analog Component Video Interface Consumer Electronics Association

Component versus composite

In a composite signal, the luminance, Brightness (Y) signal and the chrominance, Color (C) signals are encoded together into one signal. When the color components are kept as separate signals, the video is called component analog video (CAV), which requires three separate signals: the luminance signal (Y) and the color difference signals (R-Y and B-Y).

Component video does not undergo the encoding process, the color quality is noticeably better than composite video.[4]

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. 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.

See also

  • List of display interfaces

References

  1. ^ Audio/Video Overview - types of signals
  2. ^ How to Use the 9A65 Component to RGB Video Converter
  3. ^ Poynton, Charles (November 28, 2006). "Color FAQ- Frequently Asked Questions about Color". http://www.poynton.com/ColorFAQ.html. Retrieved 2009-06-28. 
  4. ^ "Video Signal: Composite vs. Component". Apple Support. 03. http://support.apple.com/kb/TA21585?viewlocale=en_US. Retrieved 25 April 2011. 

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