What is RGB?

RGB stands for Red Green and Blue, these are the 3 colours used to display a TV picture.  Using RGB the picture is sent as three separate colours corresponding to the three colours used in a TV to display the picture. A high resolution RGB picture can have a bandwidth of over 10MHz and this is without doubt the best way to send picture information to a TV or display. Component video Component video is comprised of a Y signal (this is the luminance being a mixture of red, green and blue), and two colour difference signals, referred to as either V & U or Cr & Cb respectively. Both require a sync signal to generate the required timing inside the TV so that a viewable picture can be built up. When using a DVD player it may be better to use Y Cr Cb output , as they generate these straight from the digital signals. There are more than a few options for sending the sync signal with RGB. The norm is for 75R terminated signals and 0.7V peak with higher voltage producing a brighter image. If you need to get RGB to more than one display simultaneously then the Keene Electronics scart distribution amplifier with a bandwidth of over 50Mhz is an excellent choice. 

 

A typical TV scart RGB connections are 

15

Red

11

Green or Green with sync

7

Blue

20

Composite sync

2

Audio in Right

4

Audio Ground

6

Audio in Left

16

RGB mode select

8

Control switching 

This configuration is the one most commonly used in set top boxes and DVD players so that a scart to scart lead will normally get things working. RGB is sent as RGBs (No 2 below)

Plasma screens and projectors do not usually have a scart connector and will typically have an SVGA connector (see here for pin out) or 4-5 phono / BNC connectors and use one of the many types of connection listed below

    1 Sync on green (RGsB) the sync signals are sent as a combined signal at about 0.3V along with the Green signal. In this case the green signal has a peak to peak voltage of 1V

    2 Separate composite sync (RGB s) In this case the sync signal is sent as a combined sync signal it is the norm here to use the composite video feed which has a 0.3V combined sync incorporated. You can get a small horizontal picture shift due to the sync being delayed as part of the composite video encoding. This is the most common method of sending RGB from a DVD or set top box. All 75R signals

    3 Separate combined sync (RGB S) (RGB H/V) Here the sync is sent as a combined (mixed) signal at 5V (TTL) levels. This is often found on projectors or large monitors that have four BNC as the inputs. RGB is 75R signal, S is high impedance usually > 1K

    4 Separate sync (RGB H+ V) used on SVGA connectors and large screens or projectors with 5 BNC or 5 Phono inputs. The sync here is sent as separate horizontal and vertical signals at 5V (TTL) levels. RGB is 75R signal, H and V are high impedance usually > 1K

It is worth noting that any delay in the picture relative to the sync will produce a very slight picture shift to the right and any delay in the sync relative to the picture will produce a picture shift to the left. This is apparent when using RGB picture and taking the sync from the composite video as the sync is very slightly delayed due to the encoding process. It is not normally a problem but can sometimes be noticed when switching from RGB to composite video or switching RGB sources as the delay time varies.

The Keene Electronics SyncBlaster cables are designed to convert from the RGB s signal given out by a typical DVD or set top box into RGB + H/V + V to allow connection of these sources to projectors and plasma screens that require TTL level syncs. By producing both the combined sync and separate syncs at TTL levels a wide range of compatibility is assured. Most monitors that require separate H and V syncs simply ignore the extra V sync signal. An  H + V only version can be ordered if required and would normally be supplied if the lead ordered is to an SVGA 15 pin D sub

Sometimes in equipment specifications HD is substituted for H and VD is substituted for V These are for most purposes the same, being a slightly longer and earlier version of the horizontal sync and vertical sync pulse

Inside the scart plug of a SyncBlaster cable

The SyncBlaster BlackBox will allow any to any so whatever the input sync format, with the BlackBox you can produce any of the above output formats, if need be it will remove sync from the green (RGsB)