[vdr] Re: OT: RGB Component from J2

["Reinhard Walter Buchner" <rw.buchner@freenet.de>]

Hi Tomas,

> I upgraded to a beamer with various input possibilities. Using a 
> compsite signal with 130" display isn't that fun. From what I understand 
> the best way would be to use the component input.

Aside from composite vs 130" your next problem will be 15,6kHz
AND the low DVB resolution on a 130" wall ;o))  Seriously, your
gonna see scan lines big and fat. Best bet would be to feed your
CRT with a line doubler or tripler. I can still see scan lines on 
my 8" Marquee Ultra from a quadrupled source ;o))

> Is it a false assumption just to use pin3 for blue, pin 5 for green and 
> pin 7 for red? All grounded of course.

You'll also need the "composite" pin for sync. This is composite
sync, so make sure your CRT can handle this. Otherwise you'll
need a bit of circuitry (LM1881,a NAND gate and a AND gate)
to get H & V sync out of the DVB

And lastely YUV (component) is *NOT* RGB. YUV is a brightness
signal (Y) and a color difference mix (U & V). The DVB doesn't
ouptut YUV, but rather RGBs. The "s" being composite sync.

Via a matrix you can turn RGBs und YUV, but it *IS NOT* lossless.
Of course, mathmaticians will tell you differently, but there is a
difference between "on paper" and "real world" simply called parts
tolerance.

"I" never really understood the hype around component video.
What advantages does it have? Well, just about the only one I
can see is three video lines vs 4 or 5 lines. That's *all*. It has
less bandwidth for sure. It also mixes signals, which I don't like
(at least not for high grade video). If it makes a difference in the 
world of DVB, is indeed, another question. Lastly, you are
converting around quite a bit. Your source has to encode RGB
into YUV, then you transfer it through your video chain and 
your pj once again (at the neck boards at the latest) has to
decode YUV into RGB again, because there are *NO* YUV
output devices in this world. This may lead to color mismatch
problems. Any conversion degrades video. If this is noticable
to the viewer depends on the viewer, his equipment and how
picky he is ;o))

One last thing, I'm not sure if the DVB is up to driving long
signal lines (haven't got around to trying). You are loading
the output with the capacitance of the video lines. This
holds true even if you are running true 75 ohm cable and
properly terminating the ends. Even video cards where
never meant to run long video lines, which is why a lot of
CRTers also run booster (line driver) amps in their video
chain. These boosters don't (need to) boost the voltage,
but rather properly drive the video line.

If you go the transcoder route, I would most certainly run it
through a line doubler or tripler.

Greets,
Reinhard


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