Component video

Component video is a type of analog video information that is transmitted or stored as two or more separate signals (as opposed to composite video, such as NTSC or PAL, which is a single signal).

Related Topics:
Video - Composite video - NTSC - PAL

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Most component video systems are variations of the red, green and blue signals that make up a television image. The simplest type, RGB, consists of the three discrete red, green and blue signals sent down three coaxial cables. This type is commonly used in Europe through SCART connectors, in the form of RGB plus composite sync, i.e. four of the wires in a SCART cable are used for the video signal (excluding ground wires). Outside Europe and Australasia, it is generally used for computer monitors, but rarely for consumer TV-type applications.

Related Topics:
RGB - Europe - SCART

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A slightly different type of componentization aims to separate out one colorless component, termed luminance, from components (at least two are needed) that give only color information, termed chrominance. This componentization can be approximated by a linear transformation of the sRGB color space. This is the signal type for images that is usually meant when people talk of component video today. Variants of this format include YUV, YCbCr, YPbPr and YIQ commonly used in video systems.

Related Topics:
Luminance - Chrominance - Linear transformation - SRGB - Color space - YUV - YCbCr - YPbPr - YIQ

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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, whereas in video applications it is more usual to embed the sync signal in the Y component. The latter is known as sync-on-green, due to the notion that the "green component" of an image approximates its luminance.

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Component digital video signals are sometimes referred to as 4:2:2, meaning that for every 4 bits that are dedicated to the Y component, 2 bits each are dedicated to the U & V components on both even (second 2) and odd lines (third 2) of the image. The luminance or Y channel carries most of the image detail resolveable by the human eye, and is, therefore, assigned more bits. Another common method, 4:2:0, is used on DVDs. In this case, only the even lines have color information; for the odd lines it is approximated by interpolation. This signal is often converted to 4:2:2 inside the player before it is sent out to other devices.

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S-Video is also considered a component signal, because the luminance and chrominance signals are transmitted on separate wires.

Related Topics:
S-Video - Luminance - Chrominance

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Examples of international component video standards are:

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• RS-170 RGB (525 lines, based on NTSC timings, now EIA/TIA-343)
• RS-343 RGB (525, 625 or 825 lines)
• STANAG 3350 Analogue Video Standard (NATO military version of RS-343 RGB)