[vdr] 1:1 pixel mapping - a waste of time?

Jukka Vaisanen Jukka.Vaisanen at exomi.com
Tue Jan 6 00:17:52 CET 2009


Yes, it's a good idea to get 1:1 pixel mapping on your display. Double
scaling (first pc, then display) is not a good idea, ever. 

But, some problems arise:

HDMI uses DVI signalling for the video (and audio is hidden in a
vertical blanking time slot believe it or not) so it may seem like just
another connector.. however in their finite wisdom the HDMI
standardization people decided that HDMI will not support arbitrary
resolutions, but instead only the existing (and back then, planned)
broadcast resolutions:

- 576i/p (pal) and 480i/p (ntsc)

- 720p (1280x720)

- 1080i and 1080p (1920x1080)

The world is full of TVs with 1366x768 and other weird resolutions.
There are also plasmas with 1024x768 etc "standard computer
resolutions". The big surprise to many people is that even though DVI
signalling could carry these native resolutions, the displays themselves
won't accept / sync to them. And they don't advertise them in the EDID
data so you have to force your computer to that resolution / refresh to
even try it (and fail).

The only true 720p displays I have seen are rear-projection TVs and
data/av projectors. They will accept their native resolution of 1280x720
over HDMI, however getting rid of overscan to get 1:1 is another
matter..

Then a solution:

I used to have a Panasonic plasma with a similar non-standard resolution
and I used the VGA port with it to automatically get a 1:1 pixel display
as it's intended for PC display use. Yes VGA is not optimal but at that
resolution and a 1 meter cable, who cares... Today I have a full HD
1920x1080 panel with an option for "exact scan" which gives me 1:1
pixels (without overscan) out of the box over HDMI, I just run normal
1920x1080 at 60Hz out of my computers.

And finally a question:

If someone can tell me how to get 576i over HDMI out from VDR, please
do. That way I could use my external HQV Reon video scaler to upscale
it.. Of course it would need to allow me to switch modes for 720p and
1080i also based on broadcast resolution ;)

- Vaizki


________________________________

From: vdr-bounces at linuxtv.org [mailto:vdr-bounces at linuxtv.org] On Behalf
Of Scott
Sent: 6. tammikuuta 2009 6:30
To: vdr at linuxtv.org
Subject: [vdr] 1:1 pixel mapping - a waste of time?


As Im just starting to get vdr working, I was wondering if 1:1 pixel
mapping between the video card (nvidia onboard HDMI output) and my flat
panel (Samsung plasma) is a waste of time.  When looking at a "computer"
generated image like the desktop, its going to make a difference, but
with broadcast material (SD mostly), I imagine that the material is
scaled anyway to fit the resolution of the panel (which in my case I
think is 1024x720, but that has a bit of overscan).  So it wont be 1:1
anyway, or am I wrong here?    I know this is a bit off topic, but there
seems to be a fair bit of experience here.

--
Scott 



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