Component video
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- This article is about analog component video: for the processing of color components in digital video, see digital video, Chroma subsampling and YCbCr
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.
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[edit] 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. When a signal is separated this way it 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, although many TVs do not support 1080p through component video.
[edit] 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, although it was used extensively in commercial, professional and high-end installations, as S-Video was considered sufficient for consumer use.
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)[1], or yellow (H) and black (V), or gray (H) and black (V).[2]
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.
[edit] YPbPr 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 monochromatic image carried, instead of three. 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.[3]
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.
[edit] 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.
- 9-pin Mini-DIN-connectors called "S-Video" or "TV Out" in computer video cards, which usually include an adaptor for component RCA, composite RCA and 4-pin S-Video-Mini-DIN.
[edit] S-Video analog component video
S-Video (S for Separate) is another 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. 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.
[edit] 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)
[edit] Confusion
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 YPbPr and composite video, with a software or hardware switch to determine which signal is generated. Hence, a common complaint, especially with the PlayStation 2[citation needed], 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).
[edit] References
- ^ Audio/Video Overview - types of signals
- ^ How to Use the 9A65 Component to RGB Video Converter
- ^ Poynton, Charles (November 28, 2006). Color FAQ- Frequently Asked Questions about Color. Retrieved on 2007-09-02.
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