[opendtv] Re: Overscanning on LCD TVs
- From: "Stessen, Jeroen" <jeroen.stessen@xxxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 11 Nov 2009 10:11:12 +0100
Hello,
Kilroy Hughes wrote:
> Most displays today are schizophrenic.
We prefer to say that they have different profiles for different use cases. :-)
> If you use "computer likely" inputs (DVI, VGA, etc.) they'll leave the
> picture alone if it matches a native display matrix.
It's not as if the scaler is the only problem.... There is also the issue of
signal
levels: video is supposed to be Y' = 16..235, and computers use R'G'B' = 0..255.
I'm thinking that I may have found a problem in a Digital Cinema application,
specifically the projection of Mark's Live Cinema transmissions from the Met
Opera. The HDMI output of a satellite receiver is connected to the DVI input
of a cinema projector, and the EDID channel is deliberately interrupted. The
satellite receiver must therefore convert from Y'CbCr to R'G'B', but I suspect
that it does not convert from 16..235 to 0..255. The cinema projector presumes
an sRGB signal on its DVI input, therefore it expects 0..255. The result is that
the black level is too high, and the white level is too low. What a waste...
Such problem is hard to debug if you don't have an HDMI analyzer at hand.
It would help if Mark sends some well-chosen test pictures prior to the opera.
I've had a lot of communication with Mark about this, and he's doing his best.
I'm just saying, some problems can't be solved without test data and equipment.
The scaler is actually the least of our problems, unless you must display sharp
computer desktop graphics. Reasonably anti-aliased images on a display that
is reasonably far away do _not_ suffer from a reasonably well-programmed
scaler. I should know, because my Cinema 21:9 TV (hear all about it at
***The Tech Retreat*** !) scales 2.37:1 BluRays from 1920x810p to 2560x
1080p, and the picture remains very sharp. The scaler is a non-problem, really.
We can disable the scaler via an "unscaled" option, but then the image may be
boxed in. Our most "leave-it-alone" mode may be the "game" mode, where we
want to minimize the video latency. If you're driving a car simulator, or if
you're
getting shot at, then 100 ms extra latency can be deadly to your virtual you.
Groeten,
-- Jeroen
Jeroen H. Stessen
Specialist Picture Quality
Philips Consumer Lifestyle
Advanced Technology (Eindhoven)
High Tech Campus 37 - room 8.042
5656 AE Eindhoven - Nederland
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