Composite video is the backbone of all video used in consumer and professional video products. Without composite video, higher-capability formats like component video would not be possible. Composite video uses one cable to transmit the three essential elements of video: luminance or brightness, chrominance or color and sync. Although composite video cables themselves are used less every day with better options such as component video and HDMI, understanding the roots of the video format is useful when evaluating various video-processing techniques and how video works in general.
Luminance, Chrominance and Sync
The three components of a composite video signal all work together to form a color television image. Luminance describes the overall brightness of a particular segment of the chrominance or color component of the signal. This is why different sections of the same color can have differing brightness levels at the same time. Sync is the relationship between the vertical and horizontal scan lines. Without proper alignment you would see a garbled image or no image at all. The individual elements of the signal are separated at the display, forming the images you see from your basic cable box or VCR.
If you're using a composite video cable and wish to upgrade one level to the next type of signal transmission, S-video is that step. Unlike composite, S or "separated" video carries the luminance and chrominance values on two wires or channels as opposed to one, typically allowing superior sharpness and color rendition. S-video gained prominence as an upgraded video option on certain videocassette recorders, although the resolution between S-video and composite is the same at roughly 480i.
Prior to HDMI becoming the preeminent video format in terms of quality, component video reigned supreme. Component video separates the chrominance section into its three elements of blue, red and green. On a three-channel component video signal, the luminance portion of each color is represented digitally on a per-color basis, resulting in superior resolution and color accuracy. Sync signals are consolidated on the green or "Y" cable. Component video cables can be assembled using three identical, high-quality composite cables or those used for coaxial digital audio. Component video is capable of high-definition resolutions at 1080p and beyond, with the individual electronic components governing output.
Coaxial cable is the type used to send cable and satellite television signals into your home. Although coaxial cable has high bandwidth for these duties, it can be made into a single composite or in a trio to form a component video cable. Simple screw-in RCA adapters convert the coaxial cable into composite. As with premade composite cables, three identical leads must be used when forming a component cable.
- Photodisc/Photodisc/Getty Images