Re: VGA Scan Conversion and Plasma Panels

["Keith Doxey" <keith.doxey@xxxxxxx>]

Hi Paul,

The whole are of VGA Scan conversion is a messy one.
Here in the UK we are lucky that a PAL TV picture has 625 lines (although
not all of those are visible) and at a push can get a reasonable SVGA
800x600 image on the screen. In the US they use NTSC which only has 525
lines and so they are restricted to VGA 640x480 maximum.

The quality of the displayed picture depends on a number of factors.

1. the quality of the converter. Broadcast quality ones are in the region
of
1000UKP and are obviously not in the same league as a 30 quid VGA gamer
card.

2. the quality of the tube in the TV. Just as PC monitors have different
dot
pitch so do TV tubes. Look closely at the phosphor dots or stripes on your
TV and compare them in size to your PC monitor.

If you are trying to display an image of higher resolution that the display
device can handle there will be loss of detail. This also happens with LCD
displays as well. Many of them compress a 1024x768 image to fit a 800x600
LCD and the only way to display 1000 pixels of information in 800 physical
locations is to throw 200 of them away ie drop every fifth pixel. The
results of this can be awful. Tacky ACSII graphics follow....be sure to use
a fixed font like courier for this. This is an enlarged version of the
letters A and E with a space between them

How it should look

XXX  XXXXX
X   X X
X   X X
XXXXX XXXX
X   X X
X   X X
X   X XXXXX

A well compressed image would look like this

XX  XXXX
X  X X
XXXX XXX
X  X X
X  X XXXX
squashed a bit but still legible

but many displays and converters do things like this

XXX XXXX
X    X
X    X
XXXX XXXX
X    X
X    XXXX

or

XXX XXXXX
XX
XX
XXXXXXXX
XX
XXXXXX

doesnt look pretty does it :-((

I havent tried using a Video card with TV output yet like the ATI All in
Wonder but I would imagine the results would be much better than any of the
converter cards or boxes out there due to the fact that the image was being
generated for display on a TV rather than converted from a higher
resolution.

It is possible to get good looking computer images on a TV. The Amiga
produces a quite legible image at a fairly high resolution and even the
humble BBC Micro from 1982 can display 80 character text on a TV which is
double the resolution of teletext. The only shortcoming of the BBC was a
poor PAL encoder but the RGB output is great.

When looking at Projectors and Plasma Panels in the sub 4 grand bracket,
read the specification VERY carefully. Although they say they have a VGA
input for a PC people immeadiately think "great, I'll hook the Pc up
to it".
With many of these lower cost units IT REALLY IS A VGA INPUT  640x480 MAX
!!!

We have just got 2 new 21" Mitsubishi Plasma screens at work and they
are
Video, S-Video and VGA. NOT SVGA.

Many of the 4:3 models will only do VGA
the newer and more expensive 42" widescreen 16:9 panels are great for
movies
but for PC the resolution is 852x480 which gives SVGA width but VGA height.
As I said in a previous post, the toolbars take up much of the height at
low
resolutions so you still have a problem with not much display area. Also
for
the widescreen plasma panels you need to find special video drivers to
generate the correct aspect ration from your PC. Or suffer the effects of
stretching or compressing the image.

The latest Pioneer 50" Widescreen panel is sold as XGA but is actually
1280x768 so a true XGA 1024x768 signal has black bars at the side or you
stretch it horizontally. If you run your PC at 1280 x 1024 then you fill
the
width but the image is compressed vertically. It does look good on video
though ;-))

Hopefully as TV and PC becomes more integrated the quality of tubes in TV's
will improve and so will the scan rates. Basic Multisync monitors now cost
that same or less than a 14" TV. Not long ago they were double the
price.
There are now loads of graphics cards with TV outputs and converters from
30
quid. Not long ago there were no cards with a TV output and the cheapest
converters were 100 pounds.
LCD panels are plummeting in price. The highest resolution ones are now
slightly cheaper than VGA panels were a couple of years ago.

Prices are falling and products are becoming available, the trouble is we
are too far ahead of Joe Public in our persuit of technology and so have to
wait for it to appear, or pay the high prices currently demanded.

Keith

Keith Doxey
http://www.btinternet.com/~krazy.keith
Krazy Keith's World of DIY HomeAutomation


> -----Original Message-----
> From: paul gordon [mailto:paul_gordon@xxxxxxx]
>
>
> I can add a little more to the displaying of VGA on a TV dilemma...
>
> I currently do this with my old laptop (an IBM Stinkpad), which
> has a custom
> connector for a video-out port (a tiny little 3pin plug), into which
> connects a "dongle" with a breakout box on it which has both
a phono
> (composite) and a mini-din (S-VHS) video out connectors. I have
> used both of
> these ports, and to be honest have been disappointed with the results.
I
> expected to see an improvement when I changed it from the
> composite to the
> S-video connection, but in truth, I can't really tell any difference.
>
> However, I was recently at Microsoft Tech-Ed in Amsterdam,
> I noticed that the display quality on these was
> considerably higher than I achieve at home, so I took a look
> round the back
> of one to see how it was connected, and sure enough, despite a
> plethora of
> connectors on the back, the ONLY signal wire going in to them was a
co-ax
> UHF lead... These were perfectly standard Philips domestic TV's (not
> specialised monitors.) My assumption is that, being Philips TV's,
> they are
> most likely 100Hz scan models, (which my current TV isn't). I'm
guessing
> that this may be the reason for the better image quality...
>
> Can anyone else comment on this? - has anyone tried comparing the
> same PC's
> TV out signal between a 50Hz and a 100Hz scan TV? (I'd prefer to know
if
> it's worth it before I rush out & buy one!)
>
> but then in this month's T3 I spotted an ad for a 60"
> (Yes, you read that right - 5 feet!) DLP screen, which among
> other things,
> has a direct VGA connection, so it could plug straight in to a PC
> & function
> as a monitor, as well as all the usual things. It also has a touch
screen
> option, and a PIP option. This was advertised at £4995 (inc vat),
which I
> reckon I could _JUST_ (with a little bribery) get Wife to
> accept!! I don't
> know how much the touch screen option would add to that cost, but
> wouldn't
> that be a COOL thing!! - a 5 foot wide touchscreen!!


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