[mythtv-users] VGA to component cables
Cory Papenfuss
papenfuss at me.vt.edu
Sun Jan 7 22:46:53 UTC 2007
> Hi there,
>
> I'm confused by this. VGA _by definition_ carries RGB signals, no?
>
Yes.... but that doesn't mean that other things couldn't be sent
out the DB-15 connector of a "VGA" card.
> I think you're saying that some ATi cards can, with the right
> drivers, output YPbPr through their VGA-output connector. Is this
> correct?
>
It's slightly more than drivers, but not much. There are a few
different flavors of "RGB" video. There's RGBHV with a discrete Red,
Green, Blue, Horiz, and Vert sync signal.... that's "normal" VGA RGB and
requires 5 separate signals. Once upon a time, it was relatively common
to combine the Horiz and Vert sync signal into a "composite" signal
requiring only 4. It was even relatively common to add this composite
signal onto one of the video signals... typically the Green, for
"Sync-on-green" video. That requires 3 wires and a number of workstations
did this.
This "Sync-on-green" is more or less the same thing as YPbPr,
except that the D/A on each of the video channels puts out a
color-transformed set of data. If you take a plain VGA card that can
output both:
- Sync-on-green
- Interlaced output
- 60Hz/15.7kHz sync rates
... and connect the green channel to the Y-channel of a component TV,
you'll see a nice, crisp B&W image of the green channel of the RGB video.
If you connect the other two, you'll see a nice rendition of an acid-trip
color video, since the color transformation hasn't been done.
These "breakout" cables simply do that... and the driver tells the
card to do the color transformations.
> If my understanding is correct, then the cable above would be better
> referred to as a "15-pin D-sub to component video breakout cable"; as
> you surmise it will not breakout YPbPr from a _standard vga_ (or SVGA
> or XGA &c) output.
>
Correct... but since when have consumer products been named aptly
to prevent confusion?
> The fact that we're having this discussion, and the OP's questions
> about its suitability, suggest that the website's labelling of this
> cable is misleading - one would reasonably expect to plug a "VGA-to-
> component video breakout cable" into a VGA port at one end and a
> telly's component inputs and have at least the right colours come out.
>
See above.
-Cory
--
*************************************************************************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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