Analogue Video Signals

A video signal, no matter what type, must contain the colour detail and a synchronisation signal (to tell the display how to put the colours together). In some cases the colour detail is split into black and white detail (Luminance) plus the colour streams for the signal (Chrominance), again the synchronisation tells the display how to put all this together. In others the colour stream is divided into more than one colour. It is how this is done that differentiates the following analogue videa signal types:.

Composite Video

Basic form of video used with VCRs, Laserdisc and other basic technologies. As the name might suggest all the video signal components are sent down one single coaxial cable (usually with a Yellow “Phono” plug at the ends). This format is cost effective, and will run over very long distances – however, since all the colour and sync components run down the same single cable they interfere with each other causing artefacts

S-Video (SVHS, Super-VHS, Seperated Video)

S-video offers an advantage over composite video by separating the Chrominance information (colour portion of the image) from the sync and Luminance (black and white detail). THis was common in the 80s where a full RGB studio would be expensive to build, but a composite based one was too poor a quality. The cable itself carries to coaxial connections terminated to a 4-pin mini-din plug at each end. Higher end systems will often use two BNC connections rather than the 4-pin din.

Component Video (YUV, YPbPr, YCbCr)

Component video runs down three separate coaxial cables. The image is sent in Black and White (the "Luma") down the "Y" coax often coloured green. The colour components (the "chroma") are represented on two coaxes, the "Pb" or "U" (often coloured blue) represents the the Blue portion of the image minus Luma, and the "Pr" or "V" (often red) represents the Red minus Luma. From this simple compression the receiving device can accurately regenerate the full colour image using the three seperate portions. This is a lossless compression and in fact how data is originally stored on a DVD disc. The same compression process (albeit with different scale factors) is used in PC formats such as jpeg.

RGB Video

RGB Video also sends a signal as its separate components, and offers the same quality as Component Video. The three basic colour components (Red, Green and Blue) are always seperate from one another. The sync (which tells the receiver how to reassemble the colour components) is either run along the Green component, or as a separate sync, or as two separate syncs; one for horizontal and one for vertical (PC display systems use this).

The most common use in the consumer environment is RGB with a single separate single sync commonly found on DVD players and Digital set top boxes. While it is possible to run Progressive Scan RGB this is very uncommon in consumer applications but the method of choice when using Home Cinema PCs (HCPC) or a dedicated Video Processor