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 signals comprise two or more separate signals and thus are all component-video signals. For most consumer-level video applications, the common three-cable system using BNC or RCA connectors
analog component video was used. Typical formats are
480i (480 lines visible, 525 full for NTSC) and
576i (576 lines visible, 625 full for PAL). For
personal computer displays the 15-pin DIN connector (IBM VGA) provided screen resolutions including 640×480, 800×600, 1024×768, 1152×864, 1280×1024.
RGB analog component video for a personal computer or JP21 connector for a television The various RGB (red, green, blue) analog component video standards (e.g., RGBS, RGBHV, RGsB) use no compression and impose no real limit on
color depth or resolution, but require large
bandwidth to carry the signal and contain a lot of
redundant data since each channel typically includes much of the same black-and-white image. Early personal computers such as the
IBM PS/2 offered this signal via a
VGA port. Many televisions, especially in Europe, can utilize RGB via the
SCART connector. In addition to the red, green and blue color signals, RGB requires two additional signals to synchronize 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; also the acronym HD/VD, meaning
horizontal deflection/vertical deflection, is used) • Sync on green, where a composite sync signal is overlaid on the wire used to transport the green signal (SoG, Sync on G, or RGsB). • Sync on red or sync on blue, where a composite sync signal is overlaid on either the red or blue wire • Sync on composite (not to be confused with composite sync), where the signal normally used for composite video is used alongside the RGB signal only for the purposes of sync. • Sync on luma, where the Y signal from S-Video is used alongside the RGB signal only for the purposes of sync. Composite sync is common in the European SCART connection scheme (using pins 17 [ground] and 19 [composite-out] or 20 [composite-in]). RGBS requires four wires – red, green, blue and sync. If separate cables are used, the sync cable is usually colored yellow (as is the standard for composite video) or white. 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), yellow (H) and black (V), or gray (H) and black (V).
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 line of video game consoles) 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. Sync on composite, not to be confused with composite sync, is commonly used on devices that output both composite video and RGB over SCART. The RGB signal is used for color information, while the composite video signal is only used to extract the sync information. This is generally an inferior sync method, as this often causes checkerboards to appear on an image, but the image quality is still much sharper than standalone composite video. Sync on luma is much similar to sync on composite but uses the Y signal from S-Video instead of a composite video signal. This is sometimes used on SCART since both composite video and S-Video luma ride along the same pins. This generally does not suffer from the same checkerboard issue as sync on composite, and is generally acceptable on devices that do not feature composite sync, such as the Sony PlayStation and some modded Nintendo 64 models.
Luma-based analog component video Further types of component analog video signals do not use separate red, green and blue 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 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 and
MPEG compression schemes to reduce the storage requirements for images and video (respectively). Many consumer TVs, DVD players, monitors, video projectors and other video devices at one time used output or input. 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 •
D-Terminal: Used mostly on Japanese electronics. • Three
BNC (professional) or
RCA connectors (
consumer): Typically colored green (Y), blue (PB) and red (PR). •
SCART used in Europe. •
Video-in video-out (VIVO):
9-pin Mini-DIN-connectors called "TV Out" in
computer video cards, which usually include an adaptor for component RCA, composite RCA and 4-pin
S-Video-
Mini-DIN. ==Synchronization==