OT: Composite/Component [was Re: [mythtv-users] Re: Image quality, what effects it?]

Jay R. Ashworth jra at baylink.com
Fri Aug 13 13:51:41 EDT 2004

On Fri, Aug 13, 2004 at 09:41:59AM -0400, Cory Papenfuss wrote:
> > The knee for luminance bandwidth in a traditional NTSC signal is
> > actually 4.2MHz, and, if your filtering wasn't good enough, you got
> > less.  In *theory*, it's possible to move more through an S-video link,
> > but you have enough bandwidth on the tape to store it.  S-VHS and Hi-8
> > can make use of more of what's already there, but I don't know that you
> > can usefully extend it any.
> >
> > In any event, Yves Faroudja has proved in his Super-NTSC labs that you
> > can fit into an NTSC channel a picture that would knock most
> > network-affil chief engineers *flat* on their ass; most NTSC gear is
> > truly garbage.  But then they wouldn't be able to *sell* HDTV.
> >
> > Cf. Pogue Carburetor.  :-)
>  	No big surprise there.  It's sorta a "digitally enhanced" analog signal 
> then... some post processing to recover some information to 
> deinterlace/interpolate.  I guess I recall the 4.2 MHz knee in the luminance. 
> My main question was whether or not most consumer gear takes advantage of the 
> possibility of more luminance bandwidth in S-Vid.  If your source had plenty 
> (DVD, CG, etc), you could even get more out of composite since the audio 
> subcarrier isn't necessary anymore either, right?


But most consumer equipment, even S-VHS, has a hard time making it
anywhere close to the 3.4 MHz you can get with composite.

Regular VHS is only good for about 240 lines of resolution in the first

> >>   It's almost exactly the same as the old "sync-on-green" three-coax
> >> workstation monitors. Oversimplified, Y=R+B+G, Pb=B-Y, Pr=R-Y and
> >> H/V sync is also added to Y. Realistically, they're weighted by
> >> their perceptual luminance, but for illustration it's not important.
> >
> > Well... yeah.  And you're right; I and Q are *modulated* chroma, where
> > Pr and Pb are luminance signals, so there's more difference than I let
> > on.
>  	Luminance signals... of a specific color, I guess.  True enough.... at 
> least they're baseband video information, not modulated.

Correct: they're not (sub-)carriers; they're actual video you could
hook up to a monitor.  In fact, rotating your Y-Pr-Pb cables on the
connectors can be pretty cool.  :-)

> > Yeah; this is an issue I've always wondered about; those component
> > cables can carry signals that are *not* RS-170A timed, then, right?
>  	Sure... most of the transcoder boxes (A960, etc) wouldn't inherently 
> have that limitation.  Garbage in = garbage out.  If TV's were "multisync" like 
> computer monitors, they'd even work on it.  I suspect that some of them 
> would... some would also probably blow up and die, though too.


> >>   Interesting. What do you mean exactly? Did the U-matic remix a
> >> "baseband" chrominance (demoded from the 3.58 subcarrier) onto 729kHz.
> >> Then send a differential I and Q down 2 pairs?
> >
> > No, it was like S-video: the chrominance was quadrature modulated, but
> > at 729kHz, instead of 3.58MHz; they shipped it out as Y/C; you can get
> > frequency heterodyne boxes to convert U-Matic Dub Out to "proper"
> > S-video.
> >
> > Remember, even on VHS, the NTSC color subcarrier is *not* recorded at
> > 3.58MHz.

>  	Gotcha... it's just that you said "4-wire" so I thought maybe they ran 
> them separately.  What's the color subcarrier on VHS?

Sorry, Y- Y+ C- C+.  Not 4 cables: 4 *wires*.  My fault.

I think it's down in the 600kHz area.

That's as close as anyone seems to want to go, on a short search; one
reference is here:


Here's a pretty decently written reference:


And here's a *really* nice list of tape formats:


> > I understand that the problem is specifically the Bt878 chip, which
> > wants to bus-master its PCI transfers; the video4linux at redhat list
> > archives for the last month might be informative on this.
> >
>  	?  I was basically referring to the quantity of data that had to be 
> passed.  If it were true RGB (which it's not... probably a factor of 1/2 for 
> 4:2:2), 720x480 * 30fps * 3 colors * 8bits/color = 31MBps... that's a lot of 
> data for a PCI bus.  Even with a 1/2 reduction for YUV and 1/2 D1 of 352x480, 
> that's 7.5 MBps... still plenty.  Trying to do HDTV would require 
> proportionately more.  That pretty much means it would have to encode to MPEG2 
> (or MPEG4) on the fly to stream over the PCI bus.  Lots of embedded CPU power 
> necessary for that... 4x-8x hauppauge I suppose.

Yeah.  The PcHDTV card is probably doing that.

> >>> Ok, I think it's time for someone to snipe at me now for trying to
> >>> be informative. ;-)
> >>   Me too... :)
>  	"Techo-goobers hijack mythtv thread... full story at 11!"  ;)

Time for mythtv-tech@?

For me, time for the hurricane.  Maybe Bruce will be rid of me after

-- jra
Jay R. Ashworth                                                jra at baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

	"You know: I'm a fan of photosynthesis as much as the next guy,
	but if God merely wanted us to smell the flowers, he wouldn't 
	have invented a 3GHz microprocessor and a 3D graphics board."
					-- Luke Girardi

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