More comprehensive information is available from other sites (check under Information), but I've put together some of the basic info here for easy reference.
About RGB video
RGB has become the standard for quality video for retro consoles. Unlike composite video, which sends color, brightness, and sync information down a single line, RGB sends red, green, blue, and sync signals down separate lines. This results in a cleaner, clearer image. It is more or less the same sort of signal that is sent digitally through HDMI cables in the modern era.
The main competitor in the analog space is YPbPr. Most consumers refer to this as component video, though RGB is also a type of component video. As long as the receiving TV is calibrated correctly, there is no visual difference between RGB and YPbPr. However, the downside of YPbPr is that it does not send definite color values like RGB does, so the signal is open to interpretation by the TV. Still, it is usually more convenient to hook up consoles via YPbPr as it is more common to find connections for it.
Types of sync
When using RGB video, there are a few types of sync the signal could be using.
Sync on composite
This uses the composite video signal as sync. The main benefits of using sync on composite are:
- You don't have to choose between a pure sync signal and composite video on connectors with limited pins (like an 8-pin DIN).
- It is technically the only officially supported type of sync on SCART and JP21 connectors.
- No need for resistors/capacitors as it outputs the correct signal level.
The downside is that you may get some signal interference if you are using a cheaper cable that isn't fully shielded.
Short for composite sync (because it combines horizontal and vertical sync), this is a pure sync signal, meaning that no other information is sent down the line with it. You will see this referred to as RGBs. This generally means that you don't have to worry about interference as much and can get away with cheaper cables, but it also has some downsides:
- Since it is only sending sync, you don't have composite video as a fallback.
- Requires some form of attenuation or smoothing to get it to the right signal level.
- 8-pin DIN connectors don't have enough pins to have c-sync and composite video connected, so you have to choose one. If you choose c-sync, you can't use a composite AV cable anymore.
With that in mind, a lot of consoles have a custom output jack that has many output pins so that it can support a variety of outputs. Nintendo's multiout or the AV jack on PlayStation, for example, can support composite video, s-video, and RGB. In these cases, you might as well use c-sync, but keep in mind you will need the proper resistors/capacitors in the cable. For systems with a DIN jack (PCE family), using the composite video signal for sync (with a nice, fully-shielded cable) will make the most sense. In either case, with a fully-shielded cable, there should be no visible difference between c-sync and sync on composite.
Sync on luma
This uses the sync information carried on the luma line of an s-video signal for sync. It is a cleaner type of sync than sync on composite since only brightness and sync info is carried on the line, but it is not available on all consoles. This is also the type of sync used in YPbPr signals.
Sync on green
Generally abbreviated as RGsB, sync on green sends the sync information down the green signal line. It is very uncommon, but it is used by the PS2 when sending progressive video via RGB.
This is referred to as separate sync since the horizontal (H) and vertical (V) sync information are sent down separate lines. You will see this abbreviated as RGBHV. It is the standard used by VGA video, but it is extremely uncommon to find in consoles. The one major exception is the Dreamcast since it has a VGA output option. It is not supported by SCART connectors since it requires two lines.