2009/1/6 Scott scott@waye.co.uk:
I'd say it's not a waste of time.
In general, it is a good idea to avoid any (unnecessary) processing. If you do not setup your video card to your display 1:1 to your panel's native resolution, you're most likely going to get an extra scaling of the video image (which is totally unnecessary and degrades the image).
For example, if your panel is 1024 x 720, and your video card is setup for 1280 x 768, then you'd end up first scanling a PAL/NTSC/whatever video to the 1280 x 768 and then your panel is going to scale it to 1024 x 720. You'd get better results if you'll scale straight to the native resolution of the panel via the video card, or set the video card to the native resolution of the source material and let the panel do all the scaling.
I don't know how to do the latter, and even if it is possible in all cases. In my setup, I have set up my video card to 1:1 to the panel I have (fullHD), since I have material in several different resolutions, and also use a desktop on my VDR box.It's more hassle free this way, if I would have chosen the latter case, then I would be constantly chancing resolution. It should be quite easy to setup 1:1 pixel mapping with any reasonably new display, video card and X.org, since the X.org uses EDID information quite well these days. Though, in practice, the DVB broadcasts are so much degraded by the mpeg compressing process at least here where I live, so it doesn't actually matter that much how you do the scaling ;=).
YMMV. In any case, a (single) scaling process gives better results than 2 x a scaling process.
This is the theory. But you need to remember that you are using TV set as a monitor, and typical TV sets, even FullHD ones implement overscan on HDMI input. Some TVs disable overscan via special switch.
But having overscan it means that having the 1:1 mapping is a bit harder. You need to find out how much is the real visible resolution and define X- screen to that resolution.
Naturally way to determine this is to have test patterns drawn to a screen and look closely (mag. glass) to see if you have 1:1 mapping. You need to remember that HDMI/DVI is not a digital bus, it is 'analogue'-type signal transferred in digital fashion. Why else you need porches et al at signal timing?
With this I mean that HDMI-signal does not say: -frame coming at resolution 1920x1080p50 -pixel at 0,0 use color 0,0,0 -pixel at 1,0 use color 255,255,255 -pixel at 2,0 use color 0,0,0 ...
HDMI says: - vert. sync - hor. sync - front porch time - (0,0,0),(255,255,255),(0,0,0),.....
And it is up to TV electronics where to place those pixels on LCD panel. And this is done with overscan settings etc.
- Jori
2009/1/6 jori.hamalainen@teliasonera.com:
Yes, you are right. On my Sony it is called "Täyskuiva" (in finnish), when I had not enabled it, thie TV did overscan IIRC.
I'm not sure what you mean by the above, surely you need to setup X to use the native resolution of the panel? Perhas you meant something different, as I did notice when I did my setup; that fgrlx (yuch, I'm an user of the dreadful fglrx) does a terrible underscan by default, becase it reports a larger screen area trough the HDMI that is actually used (?). I'd assume that nvidia, intel & perhaps some others do this better by default.
It is beyond me why an ouput that is used for a digital display uses any kind of over/underscan, but that really was the case. Then I stumbled on this:
http://www.phoronix.com/forums/showthread.php?p=36734#post36734
And got 1:1 mapping at all refresh rates ever since. Thoguh, I still get terrible tearing - I've heard that the radeon driver should be better in video use, but I couldn't get it to work on my card, and I also need DRI... I should've bought nvidia, damn.
I used a small program called lcdtest to test the 1:1 mapping. Believe when I say you do notice the difference =). Also I use a desktop and it is drawn exactly to the edges as it should be.
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@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
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From: vdr-bounces@linuxtv.org [mailto:vdr-bounces@linuxtv.org] On Behalf Of Scott Sent: 6. tammikuuta 2009 6:30 To: vdr@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
On Tue, 6 Jan 2009 01:17:52 +0200 "Jukka Vaisanen" Jukka.Vaisanen@exomi.com wrote:
How is "24p" (ie 24fps) managed?
24p is just a framerate, in HD it's actually 1080p but with 24 frames per second instead of 60. There are also NTSC DVDs with 24p video but that's a whole different story that we won't get into..
- Vaizki
P.S. Sorry for the awful Outlook quote style.. Will work on fixing it.
-----Original Message----- From: vdr-bounces@linuxtv.org [mailto:vdr-bounces@linuxtv.org] On Behalf Of Tony Houghton Sent: 6. tammikuuta 2009 2:08 To: vdr@linuxtv.org Subject: Re: [vdr] 1:1 pixel mapping - a waste of time?
On Tue, 6 Jan 2009 01:17:52 +0200 "Jukka Vaisanen" Jukka.Vaisanen@exomi.com wrote:
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
How is "24p" (ie 24fps) managed?
On Tue, 6 Jan 2009 02:23:51 +0200 "Jukka Vaisanen" Jukka.Vaisanen@exomi.com wrote:
Yes, I know, but what's the difference between a TV and DVD/Blu Ray player that claims to support it and one that doesn't? I'm guessing there's an extra screen mode available at 24/48/72Hz.
On Tue, Jan 06, 2009 at 01:17:52AM +0200, Jukka Vaisanen wrote:
Hello.
Please check this thread: http://www.linuxtv.org/pipermail/vdr/2008-July/017347.html
Original patches: http://lowbyte.de/vga-sync-fields/
New version: http://www.vdr-portal.de/board/thread.php?threadid=80567
Those might help.. they're about getting pure 1:1 interlaced (576i) RGB output from a VGA card.. and the new version also has some HDTV stuff, I guess. I don't read german so i'm not familiar with that..
There are also patches to maintain perfect field sync to DVB stream to avoid tearing/stutter/jerkiness.
-- Pasi
Jukka Vaisanen wrote:
HDMI interface does not limit the resolutions (TMDS link max. speed of course does but is another matter). It's mostly the "HD Ready" and "Full HD" television implementations that support only CEA-861-D modes for HDTV. Nothing would prevent HDTVs to introduce other modes in EDID and EDID extension blocks similarly as DVI computer monitors do. Though the timings would need be defined in such way that there is space for audio.
Fortunately full HD televisions typically support 1:1 pixels over HDMI so the limited amount of modes is not that bad. GFX cards will scale other resolutions such as 800x600 and 1024x768 VESA modes into the native panel resolution.
My 2c: I'm watching also a HD ready television from 2005 and despite of 2x scaling the difference with DVB PAL content is minimal to my other full HD television with only one scaling operation. The quality of the SDTV DVB-T/S content is IMHO the bottleneck instead of video scalers. Also non 1:1 pixels Gnome desktop is usable. Of course 1 pixel wide too small fonts must be avoided.
BR, Seppo
On Tue, 6 Jan 2009 04:29:55 +0000 Scott scott@waye.co.uk wrote:
With my TV I've tried running vdr-sxfe at 1360x768@60 (which the TV does accept over HDMI, but not VGA), 1280x720@50 and 720x576@50. Surprisingly 720x576 seems to look a bit rougher to me than the other two resolutions. I find 1280x720 is slightly better than 1360x768 for VDR because of the matching refresh rate.
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jori.hamalainen＠teliasonera.com -
Jukka Vaisanen -
Pasi Kärkkäinen -
Scott -
Seppo Ingalsuo -
Tony Houghton -
Ville Aakko -
Ville Skyttä