[vdr] Re: Deinterlacing

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

Hi,

> > The scaling won't help you get rid of artifacts in the stream, 
> > simply due to the MPEG algo.
 
> No, that's true, but I don't need big pixels with hard edges.

;o)) Are you planing on using a Linux or Windoz based
program? While all the Linux HTPC stuff is nice, it isn't
really usable yet in direct conjuntion with VDR. D-Scaler
is nice, but it somehow lacks further development and since
I have a myriad of sources, I'll never go the HTPC route. True
RGB input cards for a PC are either much too expensive or
lack quality. (I have two DVD players, VDR, PC and a S-VHS
running on my PJ) Plus I additionally need to be able to switch
outputs (inputs on my PJ)

> >>The idea is to do all scaling in software and use a normal graphics 
> >>board to supply RGB to the pj.

> > As noted in my other mail. A video card cannot drive a longer video
> > line correctly.
 
> Well, how long a video line do you expect a normal vga card to be able 
> to drive?

I would say your planned 4m are on the ragged edge. I'm running 
15+ meters of HQ RGBHV cable (Extron) and there is no way
my video card(s) (Nvidia and ATi) will drive this without losing
P/Q. A normal VGA card is designed to drive about 2m w/o loss.
The manufacturers do include some reserve power in the driver
cicuits, however.

> I've seen 30m cables used to drive a lcd pj at 800x600 as well as 
> 1024x768 with very little visible problems, but I'm not going to run 

Yeah, but those are pixelboxes, so it doesn't make a difference
anyway ;o)).

> > No digital PJ can RESOLVE that high a resolution.
 
> I never said I had a digital PJ,

True, but I always love those digital guys, when they talk about
a great picture. Esp those grey shades which are supposed to
resemble blacks or the screendoor effect ;o)) The high contrast
ratios and true color reproduction of a CRT are what makes a
picture become vivid and have 3D depth to it. As far as I'm
concerned digital have two advantages over CRT: one being
lighweight, the other being fast and easy to set up. That's not
enough for me to justify a move to digital, tho ;o))

> I have a Electrohome ECP3500 CRT:

;o)) Nice, so you're a CRTer! I have the big brother. It's a fully
loaded Electrohome Marquee 8500 Ultra Non-LC. I have two
RGBHV inputs (one with image shifter, one w/o), the ACON
system and for quick connects the Multistandard Decoder
board. My second CRT to play with is a modded 7500 unit.
Maybe you should check out AVSForum. A lot of CRT
geeks (including me ;o)) hang around there. One thing is for
sure: Electrohome PJ's have one of the best and cleanest video
signal paths out there. Electrohome mods for increased 
performance & PQ are numerous.

> In any case the point is that I want to deinterlace the video
> and scale  it in software and output it via a normal vga card
> at 100Hz.

There is no real need for the 100Hz. If you are watching DVD's,
(not via the DVB ;o)) too, you should aim for a straight multiple
of the frame rate, but you don't need to go that high. The problem
with high scan rates is that the picture becomes dimmer as you
are forcing the tubes and the electronics to work harder. Don't
go too high on the PJ resolution, either. I'm not quite sure what
the ECP series can actually resolve, but you should aim for a
resolution that allows you to see scan lines from 2 ft up, but
none at your viewing position. If the scan lines start to overlap,
you'll start losing resolution and the picture will become soft.
What screen size are you running? I'm planning on a 250 x 190
cm motorized (probably tab tensioned) screen. I've done some
tests with a similar sized screen and there is plenty of reserve
in the contrast & brightness controls ;o))

> I don't want to output an interlaced signal and have it mangled later...

Some of the newer external scalers like the Iscan-HD and
the Cinemateq PO Plus do a pretty good job. With the infinite
amount of adjustments it takes a while to get the best settings
(and a lot depends on the tweaking of the PJ, too). But, hey,
that's part of the fun of owning a CRT ;o))

Greets,
Reinhard


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