Component video
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Component video is a type of 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).
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 wires. This type is commonly used in Europe through SCART connectors. Outside Europe, it is generally used for computer monitors, but rarely for TV-type applications.
Another type consists of R-Y, B-Y and Y, delivered the same way. This is the signal type that is usually meant when people talk of component video today. Y is the luminance channel, B-Y (also called U or Cb) is the blue component minus the luminance information, and R-Y (also called V or Cr) is the red component minus the luminance information. Variants of this format include YUV, YCbCr, YPbPr and YIQ.
In component systems, the synchronization pulses can either be transmitted in one or usually 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 green or Y component. The former is known as sync-on-green.
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 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.
S-Video is also considered a component signal, because the luminance and chrominance (color) signals are transmitted on separate wires.
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 825 lines)
- STANAG 3350 Analogue Video Standard (NATO military version of RS-343 RGB)de:Komponenten-Videokabel