[vdr] Re: Deinterlacing

[Emil Naepflein <Emil.Naepflein@philosys.de>]

On Sat, 19 Jun 2004 12:57:37 +0200, "Reinhard Walter Buchner"
<rw.buchner@freenet.de> wrote:

> The problem is that ANY kind of "fiddeling" with the video signal
> will degrade its performance. This introduces background noise
> at least. At worst it starts smearing colors or causes pixel shift
> (a problem of the digital display units). The problem is that a
> digital PJ isn't good enough (sorry) to truely show the problems
> in the video chain. A digital PJ for example needs to rasterize the
> picture information to fit the LCD panel. 

A digital projector is reproducing the image exactly with the same
resolution it is on a DVD or is received with DVB. In contrast a CRT
projector is averaging out the pixels in a horizontal line depending of
it's bandwidth. Vertically there is absolutely no difference between
digital and CRT. On a CRT you will see horizontal lines depending on the
viewing distance and on a digital projector you see the same. 

> This rastering step is
> what leads to the effect known as screendoor. 

No, screendoor is depending on the fill factor of the pixels of the
digital display, the resolution of the display and the viewing distance.
LCD have a low fill factor and therefor the screendoor is visable from
large distance of about 2.5-3 times the image width even with XGA
resolution. XGA DLP projectors show the screendoor at about 2 times the
screen width, and DILA projectors at about 1.5 times the screen width.
Go to avsforum and educate yourself about digital technology. There are
long threads with a lot of analysis about screendoor of all kind of
digital projectors with image that show the effect. As long as the
viewing distance is large enough you see exactly the image that is on a
DVD without any screen door. My setup is even better because I use a
ISCO anamorphic lens.

> Exactly because of
> the reproduction quality and the minimal amount of "fiddeling"
> that is done to a video signal in a CRT is what makes them highly
> desireable for HT geeks. 

That's the same with analog recordings, analog tube amplifiers, and so
on. It's a matter of taste. ;-) In reality a CRT projector is never
reproducing the image in the same way as it is on the source because it
is just averaging out the horizontal pixels.

> CRTs are still in use by the NASA or
> Lufthansa training centers for exactly those reasons. 

That doesn't prove anything.

> My 8500
> Ultra costs in excess of 50 000 Euro if I had bought it new. I had
> a look at several digital models beforehand (price range up to 10K
> Euro) and none provided really satisifing pictures.

That's is just a matter of taste. What you are finding satisfying may
not be satisfying for others. There is just more than the technology
which finallys lead to a decision.

> I know you are a VDR geek (meant in the nicest of ways!), so I
> really wonder why you bought a digital display unit ;o))

Because it is the best unit in my environment. For a CRT projector you
need a dedicated room to optimize everything to the limit. My projector
is setup in a normal living room and is absolutely hidden by a projector
lift just like the screen which is a tab-tensioned DaLite High Contrast
Cinema Vision. Both move out and in to the ceiling on a press of a
button. The 1.500 Lumen and the anamorphic lens I use give a punch of
the picture even if it is not completely dark. And if it is completely
dark you see absolutley no screen door from our viewing distance of
about 1.8 screen width. The image is just as seemless like with a CRT
projector. Believe me, I have seen a great number of different setups at
dealers and other HT enthusiasts and I am still happy with my setup.
Each decision is finally a compromise.

> 
> > > RGB is the only way to go.
> 
> > Don't agree, especially not when you have cable runs of 10+ meters and
> > with the output of the DVB-S card. The image is just to noisy.
> 
> Emil, I was talking in general here (but including the DVB ;o)). 
> <snip>

Did you ever use the RGB signal of a DVB-S card?
I tested it and it was not better than S-Video because there is a lot of
noise from the computer.

You don't have to explain the basics video technology to me. ;-)
I am active on avsforum since 1998 (lost registration once because I
wasn't active for more than 6 month) and did a lot of work regarding
digital projectors, i.e. anamorphic lens, screen door effect, color
calibration with photographic filters, ... I did a lot of tweaking and
pioneering in my setup which now is general knowledge in the forum.  

> I WILL believe you that for you, S-Video is better. However, this
> depends on how your PJ processes the signal AND what is in the
> video signal path inside your PJ. I have seen a lot of DLPs with
> internal scalers that can be bypassed, but they use electronic
> switches (chips instead of relays) which reduce bandwidth and
> degrade video quality

It has absolutely nothing to do with the PJ because I tested everything
with standard TVs taking the native RGB signal (of course with proper
termination). The noise was to large for me an the S-video was clean.

> > That is exactly what I am saying. Anyway, the DVB-S card is extended
> > with a SDI interface all problems are gone. ;-)
> 
> No ;o)) because transponder bandwith is expensive. That's why a lot
> of films are shown in 352 x 288 and you can hardly call that quality ;o))

Most of the recordings I have are recorded with 704x576 anamorphic with
data rates of more than 3.5 Mbps. Only a few recordings have are
resolution of 480x576. I never saw a transmission with the low
resolution you mentioned. A lot of the recordings are better of a
average DVD. BTW, I currently have 421 recordings with 1.1 TB on my 2+
TB disk storage. :-) The average data rate is 3.6 Mbps.

> Secondly the MPEG-2 algo simply introduces artifacts, because it
> cuts down on the information in the stream. Adding a digital
> transmission path to the DVB output stage won't change this root
> problem. HDTV, once introduced, will change some of this, but our
> beloved FF cards (actually the AV711x chip) can't handle HDTV,
> causing it to crash. So we will need to rely on Convergence or
> some other company to write a firmware for newer, HDTV capable,
> DVB-S cards. I don't know if *that* will ever happen.

You can receive HDTV with a standard Nova card. But then you need
another way to decode the stream. A feature to decode onto the installed
graphic card is still missing in VDR. 

Cheers,
Emil