Quality of analogue video connections

In order of quality (highest at the top) these are the most common standards used to connect video equipment such as DVD players, projectors, cameras, etc. Each of these standards is described in detail later. Sync signals are for timing, to ensure that picture lines and frames start when they should. Digital standards require a different connection. The usual one is HDMI which has its own page. It is possible that a wireless system calledFlywire will solve many of the current connection problems soon.

Name	Signal names
RGB	R, G, B (+ sync?)
Component video	Y, Pr (R-Y), Pb (B - Y)
S-video	Y, C
Composite video	One signal (PAL, NTSC)

Symbols used:

R	Red
G	Green
B	Blue
Y	Luminance (Black and white brightness)
C	Chrominance (Colour information)

RGB

Here each colour - Red, Green, Blue - is sent down a separate cable. An additional wire is frequently used for sync and coloured yellow. The usual connector is a phono (RCA) connector though BNC may be used. Other connectors that are used are 15 pin SVGA (DB15HV), 9-pin D and SCART. Three high quality 75 ohm cables are needed, such as RG59 or RG6. Four are needed if the yellow separate sync signal is used.

Signal symbol	Signal	Connector/ socket colour
Y	Luminance (B/W) and horizontal and vertical sync	Green (used because the eye's sensitivity to green gives the best approximation)
Pr	R - Y (lum)	Red
Pb	B - Y (lum)	Blue

Three high quality 75 ohm cables are needed, such as RG59 or RG6. This connection is capable of carrying high definition (HD) video up to 1080i.

S-video

The component video signal is split into three parts; black and white information (Y), and two colour difference signals (Pb and Pr). S-Video keeps the all-important black and white (Y) information separate, and combines the colour difference signals into a single colour signal (C). Instead of three separate signals going to the display device, there are now two separate signals. This results in a small degradation of the colour information, but you still get an exceptionally good picture from this signal. The usual connector is a four-pin mini DIN, though sometimes a seven-pin one is used. Standard multi-core cable with two separately-screened cores can be used up to 15 metres or so. For greater lengths use two RG59 (or RG6) coaxial cables. Then it can be used for perhaps 30 metres without noticeable picture quality loss.

Normal four-pin connector

Pin	Signal	Usual core colour
1	Y Ground	Braid on red
2	C Ground	Braid on white
3	Y Intensity Luminance	Red
4	C Colour Chrominance	White

Composite video

Composite video is a single video signal that includes all sync, black and white and colour information in same signal. One 75 ohm coaxial cable is used, with phono or BNC connectors which are usually colour-coded yellow. The centre pin carries the signal and the outer shield of the connector is signal ground