Will S-video give Ok image quality?

Hi,

Haven't bought a beagleboard yet, but I'm planning to. Problem is I
don't have a DVI monitor. My idea is instead to use a small (about 7"
640x480) TFT LCD monitor with S-video or composite in. Have anyone
tried something similar? What kind of quality can I expect compared to
VGA?

Reagards,
Kristian

xkrja wrote:

Hi,

Haven't bought a beagleboard yet, but I'm planning to. Problem is I
don't have a DVI monitor. My idea is instead to use a small (about 7"
640x480) TFT LCD monitor with S-video or composite in. Have anyone
tried something similar? What kind of quality can I expect compared to
VGA?

S-video, and composite more so, always gives rubbish quality. It was
designed that way.

Hmm... I thought so. Well, thanks for the reply.

xkrja wrote:

xkrja wrote:

> Hi,

> Haven't bought a beagleboard yet, but I'm planning to. Problem is I
> don't have a DVI monitor. My idea is instead to use a small (about 7"
> 640x480) TFT LCD monitor with S-video or composite in. Have anyone
> tried something similar? What kind of quality can I expect compared to
> VGA?

S-video, and composite more so, always gives rubbish quality. It was
designed that way.

Hmm... I thought so. Well, thanks for the reply.

Let me clarify that, as far as I know, the s-video on the beagle board is
no worse than other s-video. The trouble is that the s-video signal simply
doesn't have enough bandwidth to provide a sharp picture.

Måns Rullgård wrote:

xkrja wrote:

xkrja wrote:

Hi,
Haven't bought a beagleboard yet, but I'm planning to. Problem is I
don't have a DVI monitor. My idea is instead to use a small (about 7"
640x480) TFT LCD monitor with S-video or composite in. Have anyone
tried something similar? What kind of quality can I expect compared to
VGA?

S-video, and composite more so, always gives rubbish quality. It was
designed that way.

Hmm... I thought so. Well, thanks for the reply.

Let me clarify that, as far as I know, the s-video on the beagle board is
no worse than other s-video. The trouble is that the s-video signal simply
doesn't have enough bandwidth to provide a sharp picture.

But on a 7" VGA TFT, can you really tell the difference?

With decent cables and attention to avoiding interference, I've found S-video
and composite to be just fine with such a small display. The fact that the
display is so small gives you some room for less-than-HDTV signal quality.

b.g.

Bill Gatliff wrote:

Måns Rullgård wrote:

xkrja wrote:

xkrja wrote:

Hi,
Haven't bought a beagleboard yet, but I'm planning to. Problem is I
don't have a DVI monitor. My idea is instead to use a small (about 7"
640x480) TFT LCD monitor with S-video or composite in. Have anyone
tried something similar? What kind of quality can I expect compared to
VGA?

S-video, and composite more so, always gives rubbish quality. It was
designed that way.

Hmm... I thought so. Well, thanks for the reply.

Let me clarify that, as far as I know, the s-video on the beagle board is
no worse than other s-video. The trouble is that the s-video signal simply
doesn't have enough bandwidth to provide a sharp picture.

But on a 7" VGA TFT, can you really tell the difference?

On a TFT display, probably. The final result depends a lot on the
deinterlacing and other processing done by the display.

Måns Rullgård wrote:

On a TFT display, probably. The final result depends a lot on the
deinterlacing and other processing done by the display.

Ok. You sound like you know more about this than I do. :slight_smile:

Assuming you had to go this route, can you recommend any hardware that would
give you hope for the best possible results? Or any hardware to avoid?

b.g.

Bill Gatliff wrote:

Måns Rullgård wrote:

On a TFT display, probably. The final result depends a lot on the
deinterlacing and other processing done by the display.

Ok. You sound like you know more about this than I do. :slight_smile:

Assuming you had to go this route, can you recommend any hardware that would
give you hope for the best possible results? Or any hardware to avoid?

A CRT is likely to look better, since it handles the interlaced signal
directly. Keep in mind that s-video is only intended for TV images. A
typical computer "desktop" will almost certainly look dreadful regardless
of the display type. The s-video signal doesn't have enough analogue
bandwidth for the sharp edges present in a normal GUI. A black to white
transition takes two or three pixels, and red to blue even more. This
is not much of a problem for typical TV images (from a camera), but becomes
very noticeable when used for a computer display. Add to this the flicker
introduced by the interlacing.

Ok, it seems like s-video isn't the way to go if I would use the
beagleboard (and monitor) for writing and reading (among other
things). I also have a 6.5" TFT LCD with 18-bit interface (32 pin).
It's TTL interface I assume. Can any of you guys recommend a way to
interface this display with the Beagleboard?

Thanks!

D/K sales a DVI-D to LVDS/TTL, ALR-1400, and another company Aaeon makes something similar.

http://www.voxtechnologies.com/embedded-solutions/compact-pci/tf-per-v01b-a10-01
http://search.digikey.com/scripts/dksearch/dksus.dll?Detail?name=586-1016-ND

Gerald

I'll check these converter boards out.

How hard would it be to get to the LCD signals before they are
converted in the TFP410 chip? Would it be possible to drive the 18-bit
display directly from these signals then? I just want to do a as cheap
as possible solution, thats why I'm asking.

Kristian

Kristian,

I will be trying just this at the weekend if all goes to plan; the
idea has been discussed a couple of times on the list before.
Currently it would require (something like) desoldering the TFP410 and
using its pads to access the signals, buffering them from 1.8V to 3.3V.

Hopefully, if a revision D Beagleboard is ever designed, there will be
a discussion about making this easier (e.g. adding a header for the
LCD data) -- it's a subject that keeps coming up! :slight_smile:

Regards,

Matt

There is a version coming that will make accessing the LCD signals easier. But, it is still a ways out.

Gerald

Matt, if you are successfull, can you describe more in detail how you
did it? It would be much appreciated. Just one thought, would it be
possible to solder the new connections ontop of the TFP410 connector
legs instead of removing the whole thing?

And Gerald, do you know approximately when this new version will be
out?

Thanks for your replies,

Kristian

FYI, it seems like it's not possible to use the Aaeon DVI to TTL
converter PER-V01B for the BeagleBoard. A reply from Aaeon read:

"Please kindly be informed that it's NOT possible to use with other
mainboards or graphics cards since PER-V01B is designed to work under
our mainboard Gene-8310 only."

Kristian

It will be early next year at this point. That could slip if several things don’t go right.

Gerald