RGB<->NTSC Video Question

[myrmidon]

Hi There,

I have a question about various video standards and NTSC/PAL standards.


S-Video and Composite Video
Both S-Video and Composite Video are always in PAL, NTSC or SECAM format.

RGB
From what I understand, RGB is a 15Khz signal that does NOT come in PAL/NTSC/SECAM format, but rather in a global RGB format. This means that arcade machines all round the world can use each other's monitors (except for the varying AC voltage), and that there is no PAL vs. NTSC problem in the Arcade world. Is this true?

My Question
So, if my assumption above is true, at which point in the 'video stack' (for lack of a better term), is the PAL/NTSC/SECAM standard introduced to the signal?

Regards
Olaf

[Barkuti]

S-Video and Composite Video
Both S-Video and Composite Video are always in PAL, NTSC or SECAM format.

No.
S-video/composite video are both signal formats, but don't relate to the characteristics of the video being encoded in it. These signals can be found at the different stages of the TV signal decoding process. Much like component and RGB itself. This is the decoding order: Radio Frecuency -> Composite video -> S-video (chroma + luma) -> Component video (YUV) -> RGB video (RGBHV), the latter one being the "raw" signal of a CRT, directly feeding the sync circuits and video amplifier.
That signal terminology, however, is often referred when speaking about game consoles and such, to speak about video connectivity options. Yet signals couldn't care less about TV system standards like resolution, refresh rates, etc. It's only that 99% of the time S-video and composite is used to encode a (insert TV standard)-like signal. For example, NTSC defines a 525 line mode, interlaced 59.94 Hz field refresh rate, 29.97 frames per second, and it's early color encoding peculiarities.

RGB
From what I understand, RGB is a 15Khz signal that does NOT come in PAL/NTSC/SECAM format, but rather in a global RGB format. This means that arcade machines all round the world can use each other's monitors (except for the varying AC voltage), and that there is no PAL vs. NTSC problem in the Arcade world. Is this true?

RGB is not a 15 KHz signal. RGB is a group of up to 5 different signals, and it's not related to the horizontal scan frequency being used. You can use whatever frequencies you need to meet your video mode requirements as long as your equipment is up to those standards.
If, for example, you're watching your CRT desktop at 1024 x 768 x 85 Hz, then tipically your graphics card will be feeding your monitor with a ~68.7 KHz Hsync frequency RGBHV video signal.
In the arcade and computer monitor world TV systems don't exist, it has no sense. Connection between video circuitry and video displays is done with high quality short cables, so there's no need to encode the signal in any format for bandwidth saving purposes, much less in a TV system. Just RGB and you.

My Question
So, if my assumption above is true, at which point in the 'video stack' (for lack of a better term), is the PAL/NTSC/SECAM standard introduced to the signal?

It's not "introduced". The signal is either encoded that way or not.


Cheers

[myrmidon]

Thanks for the detailed response Barkuti.

Therefore, in the example of using the RGB output from an XBox (through the use of the SCART connector), this therefore taps into the video circuitry 'before' it gets mixed to composite/s-video (which also then get encoded into PAL/NTSC etc)

This is very interesting, because it means that I would be able to connect my PAL PSOne (which I have been unable to use since I moved to the US) to my JAMMA arcade cabinet by simply getting the appropriate RGB Sync and Ground pins.
 
Aaah, a new plan springs to mind :-)