[opendtv] Re: 1080p questions
- From: "Stessen, Jeroen" <jeroen.stessen@xxxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 8 Dec 2009 17:01:20 +0100
Yo,
John Shutt:
Ø However, my original question was a bit simpler. I wondered what would
happen if you
Ø tried to use LCD shutter glasses with existing displays, as you originally
proposed.
I'm with you.
Ø I have two LCD displays in my home. When I wear polarized sunglasses and
view my
Ø LCD television, the image is blocked out if I tilt my head 45 degrees to the
right (from
Ø my perspective), and fully bright if I tilt my head 45 degrees to the left.
My other LCD
Ø display behaves in the opposite manner. when I tilt my head 45 degrees to
the left,
Ø the image is blocked out.
It is typical of TN (twisted nematic) panels to have the polarizers at a 45
degree angle,
because this maximizes the contrast ratio for the most used viewing angles
(left, right
and top). For a display in a car the contrast may be optimized for the driver's
head
position, which may be at a 45 degree viewing angle. Then the polarizers are
not 45*
rotated, which is a good thing, because the driver may be wearing Polaroid
glasses.
Ø Obviously both LCD manufacturers made their displays with the final
polarizer on a
Ø 45 degree bias to horizontal in order to minimize the blocking effect of
someone viewing
Ø while wearing polarized sunglasses (which are vertically polarized.)
Not ! The optimum transmission is on 45 degrees in the other direction. That
the two
manufacturers chose opposite 45 degree angles is probably just a coincidence.
Ø I've also noticed this same effect on gas pumps with LCD displays, and with
in-car navigation screen displays.
Same story, except here they have to consider that the user is wearing
Polaroids.
So if you do the test, I expect that you get black with the glasses vertical.
Ø So my question was what effect wearing LCD shutter glasses would have on the
Ø viewing experience. If the glasses had their final polarization lenses on
the same
Ø bias as the LCD television, then when the glasses were in the "clear" mode
all
Ø of the light would get through. However, this same bias on another
television might
Ø block all light!
Note that it is a different story for the better quality LCD panels, that use
the IPS or
VA mode. Then the contrast ratio is more or less independent of the viewing
angle
(azimuth !), so the angle of the polarizers can be chosen at random. It may be
the
same for all panels, so I would expect that all higher-priced TVs perform the
same
with shutter glasses, and there is no such problem as you describe.
I'm not sure about the 3D computer screens that are now being delivered. For the
required short response time I would expect them to use TN technology, so maybe
they come with special shutter glasses with polarizers under 45 degrees ?
Ø So the only way to make glasses compatible with all LCD televisions is to
have
Ø the final polarization either vertical or horizontal, guaranteeing that
everybody will
Ø see the image, but also that everybody will experience reduced brightness and
Ø contrast, unless they cock their head like a Collie hearing her master speak.
I see multiple solutions:
- standardize the polarization direction (at least for the IPS and VA
panels)
- apply a retarder to create circular polarization, and the same at
the glasses
- make two different types of glasses (horizontal and vertical first
polarizer)
- make shutter glasses that are not based on polarization, which would
be a very
good thing for displays that do not emit already polarized light (plasma, DLP)
- move the shutter to the front of the display and use passive
(circular polarizer)
glasses, this is what RealD does with its Z-plate (active retarder)
If you have to buy $100 active glasses for each family member, it soon becomes
more
efficient to make the display a bit more expensive instead. Our local Pathé
cinema is
now moving from XpanD to RealD, just in time for the holiday season and Avatar,
and is expecting to give away (!) 1000 RealD glasses per day during the peak
days.
Imagine the logistics nightmare of having to collect, clean, check, recharge,
1000
active shutter glasses per day. Minus the ones that get stolen, of course.
Groeten,
-- Jeroen (no fan of shutters)
Jeroen H. Stessen
Specialist Picture Quality
Philips Consumer Lifestyle
Advanced Technology (Eindhoven)
High Tech Campus 37 - room 8.042
5656 AE Eindhoven - Nederland
Office mobex: (27) 99650
VoipBuster: +31.85.785.3611 (VoIP-in to PC)
Mobile 1: +31.6.1389.2492 (office gsm)
Mobile 2: +31.6.4468.0021 (personal gsm)
E-mail 1:
Jeroen.Stessen@xxxxxxxxxxx<mailto:Jeroen.Stessen@xxxxxxxxxxx>
E-mail 2:
Jeroen.Stessen@xxxxxxxxxx<mailto:Jeroen.Stessen@xxxxxxxxxx>
Website: www.consumer.philips.com<http://www.consumer.philips.com>
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