Analog Video Signal Types

Analog Video Signal Types

This describes how video is transmitted. When connecting to video equipment, the nature of the signal has a direct correlation with quality. In general, an analog video signal is comprised of luma (brightness) and chroma (color) components. How those signals are combined together or kept separate affect the video quality and specifically the fidelity or resolution of the color information.

Summary Of Quality

From best to worst:

1. Component
2. Y/C (S-Video)
3. Composite

Although a video recording may be of a very good quality, if the connection from one device to another is not, then the final video quality is less than the original recorded quality. For example, if the recording is component, but then a composite connection is made to another video device- the final quality is only at a composite quality, and the color fidelity is compromised.

Composite: A video signal where the luma and chroma elements are combined together into a single signal. Used in NTSC and PAL. Labeled as Composite, CVBS or Video (on consumer equipment). The most common signal connection on analog consumer equipment, like TV's, VCR's and consumer video cameras. Lowest quality color resolution in use today. Not acceptable for post production needs like chroma keying, as the combined luma and chroma signals can not be accurately or precisely decoded. Display on television is also less than ideal as the signal needs to be decoded/converted back into red, green and blue intensities for display. Visual artifacts due to the nature of this signal include issues like dot crawl, where you see an animated checkerboard pattern along vertical color transitions.

May be connected by a coax cable with a BNC connector or with a yellow RCA connector on consumer equipment.

Y/C: Stands for luma (Y) and chroma (C). Also referred to as S-Video (as this is the most common connection type that's used, although it may be found in studio environments with a BNC connection).

This is the next step up in quality from composite. Y/C transmits the video signal with the luma and chroma components kept separate. Color is initially separated into 2 color difference components, but with Y/C video the color components are combined together. Although the color components are combined, they are still kept separate from the luma component, leading to better color fidelity than composite.

Component: The best quality for analog video. This signal type maintains luma and both color difference components all separately. Three cables connect component video, one for luma and one for each of the color difference components. Although the cables and the interfaces are often color coded red, green and blue- they are usually connecting luma, and two color difference components, but not direct red, green and blue signals.

The connections on decks and other video equipment are labeled as Y, R-Y, B-Y or Y Pb Pr.

 
This maintains the highest quality for recording, monitoring, and post production applications like chroma-keying. Although not common, in some studio environments, component video is actually conveyed by three cables transmitting separate red, green and blues signals (not luma and color difference channels).

Analog signal pitfalls: all analog video is transmitted by electrical signals which are prone to interference, distortion and quality loss when transmitted. Copying an analog source results in "generation loss", a noticeable deterioration of quality. Transmitting digital video does not incur this kind of generation loss.