[mythtv-users] *huge* difference in picture quality..

[Maarten]

On Wednesday 26 May 2004 17:04, Henk Poley wrote:
> Op woensdag 26 mei 2004 16:38, schreef Craig Tinson:
> > Out of curiosity I moved the backend server to the bedroom.. and
> > exchanged the coax to a 1 meter composite cable I had laying around..
> > this plugged into the cable box via a scart connector (with passthrough
> > back to the portable tv in the bedroom)
> >
> > *wow*
> >
> > it's now absolutely perfect.. I seriously cannot distinguish from the
> > original source and the resulting picture I have on my frontend back in
> > the front room...
> >
> > if you are like me and are using the coax output from a cable or sky box
> > in the uk.. *go and get a compositive cable and scart converter from
> > maplins or such*
>
> Are you sure? Maybe you should try S-Video and don't believe your eyes?
> Composite is rather crappy since it jams all the video info over one wire.
> S-Video has split channels for each of the colors (RGB?) and hue, if I'm
> not mistaken. Composite looks 'fuzzy'.

Not true. Composite is by no means 'crappy'. I'll give you that SVideo and RGB 
are better, but the difference is often minimal. By contrast, the difference 
between Coax and composite is indeed HUGE.  More on that below...

SVideo is not split channels for color. That is called RGB (funny).  The fact 
is, you can split up the full information in three ways:  One is where you 
send the luminance information of all three primary colors over separate 
channels (RGB). Another is where you have all color information on one 
channel (let's say HUE) and the luminance info on another (SVideo). The third 
is the combined luminance and chrominance(color) info on one wire (composite)

Now you lose a bit when extracting the different information stream again, 
therefore RGB is best, second is SVideo, third is composite. Thus far, you're 
right.

> I personaly have had bad luck with SCART converters, bleeding colors, no
> colors, etc.

Yeah, SCART can be its own nightmare since it tries to accomodate ALL three 
standards above. But if something goes wrong between two appliances, chances 
are that A sends RGB but B expects Svideo. Or other scenarios.  In those case 
you can end up with a plethora of errors, from bleeding colors through B/W up 
to interference, blockiness, etc.   I've been there... :( 

> > I was blown away.. and the wifes mouth dropped open when she came home
> > and saw the difference...
> >
> > just thought I'd share.. I wasn't aware of the fact that composite is
> > *so* much better than coax...
>
> It shouldn't... Coax is shielded and has thicker wires, composite cables
> are regularly not shielded. Though it's probably that the cable box just
> has really bad coax output, possibly even with something like macrovision
> applied.

We're not talking about the medium Coax here but with the information that is 
sent.  As it happens, that is not a _VIDEO_ signal, but an _AIR_ signal, as 
you would get out of a roof antenna.  That makes a HUGE difference, for many 
reasons: It is on a very high frequency, in the hundreds of Megahertz as 
opposed to video which ranges in the low Megahertz range, or even below that.  
So shielding and cable properties matter much more.  The second and even more 
important reason is that the videosignal has to be modulated onto that HF 
signal (which is called the carrier).  And most all domestic modulators and 
de-modulators are of bad to mediocre quality.  So you you lose three times:
First you modulate a video signal, then you send it over coax, and you 
demodulate it again to get that "same" video signal you started out with.

That is why using any of {composite, svideo, RGB} will make a huge difference 
to using the coax antenna signal.

I can't believe this is not [in] a FAQ somewhere.  It should be.  
Oh yeah, if people feel that what I just wrote is indeed correct (cause I 
don't want to be arrogant ;-) please feel free to put it in the Wiki...!

Maarten 


> 	Henk Poley <><
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