[opendtv] Re: 1080p questions
- From: "Stessen, Jeroen" <jeroen.stessen@xxxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 7 Dec 2009 09:14:25 +0100
Hello all,
Mark Aitken wrote:
Ø You say "They stay lit only as long as the sustain pulses are applied to the
row drivers."
Ø Is there not a persistence factor wrt the phosphors? Not quite truly
binary...but almost.
Yes, you are right. The persistence is in the order of a few milliseconds, like
a
CRT. It might be a little longer than a CRT, because phosphors that are
energized
by UV light may be different from phosphors that are energized by electron
beams.
There was a time when we had a plasma panel that had a green phosphor that was
significantly slower than the red and blue phosphors. Every moving object had a
green trail behind it. Not a good idea...
John Shutt asked:
Ø What is the effect of wearing polarized glasses (LCD shutters on 3D glasses
Ø are by definition polarized lenses) when viewing an LCD display?
The effect, whatever it is, is intentional ! I was referring to 3D displays of
the
"Arisawa" or "X-pol" type. In front of the last polarizer ("analyzer") a
striped retarder
is applied. This changes the linear polarization of the light into alternately
left and
right circular polarized light. The glasses, which are exactly like the RealD
glasses in
the cinema, have left and right circular polarized filters. The result is that
one eye
sees only the odd lines, and the other eye sees only the even lines. Each eye
sees
only 540 lines. Other than this loss of resolution, and the loss of 50%
brightness, and
often some vertical aliasing due to insufficient anti-aliasing filtering, it is
a very
pleasant experience ! Without the glasses the same display can be used as a 2D
display with the full 1080p resolution. There may be some light loss because of
a
black matrix that is applied to increase the vertical viewing angle. This is
because
the striped retarder is currently applied on the wrong side of the glass, so
there is a
vertical parallax issue. An in-cell retarder would solve that, it is in the
pipeline.
In the RealD cinema it all works differently. RealD puts a "Z-plate" in front
of the
projector. This is an active retarder. The DLP projector is run at a higher
frame rate,
typically 144 Hz, and at alternately produces frames for the left or right eye.
The
retarder converts the light into alternately left or right circular polarized
light, and the
glasses block the wrong half of that, so that each eye receives 72 frames per
second.
If the light was not already polarized, and if a recycling polarizer is not
used, then the
light output is only 25% per eye. But you get full 1080p resolution per eye. The
projection screen must be polarization preserving, so it must be replaced with a
"silverscreen". The glasses are very cheap (< $1), usually disposable.
A minor variation on the theme is from Dolby, it does not work with
polarization but
with multi-band color filters. A rotating color filter plate creates two
different color
spectra for alternate frames, and the two lenses in the passive glasses each
pass
only one of the spectra. Each eye gets a different color gamut, and the content
must
be corrected for the two different color gamuts. The glasses are expensive (some
tens of $), so they must be recycled and cleaned.
The XpanD cinema works differently. Nothing is put in front of the projector,
and
everybody gets to wear shutter glasses. These are essentially 1-pixel LCDs.
Again
the projector is run at 144 Hz, and at alternately produces frames for the left
or right
eye. The shutter glasses block half of that, so that each eye receives 72
frames per
second. The phase of the shutters is controlled by an infra-red signal from an
emitter above the projector. The glasses contain a receiver, and a battery.
If the light was not already polarized, and if a recycling polarizer is not
used, then
the polarizers of the glasses block half of that, and the shutter action blocks
another
half of that, so the light output is only 25% per eye. But you get full 1080p
resolution per eye. The projection screen can be anything, but the glasses are
expensive (~ $100), so they must be recycled, cleaned, recharged, ...
A 3D DLP projector in the home is the same as the DLP projector in the cinema,
so
generally the XpanD method is applied. It's probably run at 120 Hz, so each eye
gets
60 frames per second at 1080p resolution. Plasma panels, e.g. from Panasonic, do
the same. There may be a minor issue with phosphor persistence.
Finally, a 3D LCD panel (or projector), may also be run with frame-sequential
XpanD
shutter glasses. The response time of the panel now becomes a major issue,
causing
some crosstalk between the left and right images. It may be improved by running
the
panel at 240 Hz, inserting black fields (60 times: left, black, right, black,
...), scanning
the backlight, and keeping the duty cycle of the 2 glasses well below 50% each.
The light output will drop a lot, even though the light was already linearly
polarized so
the LCD shutter glasses do not take away another 50%. There is the promise of
significantly faster LCD panels, based on OBC or Bluephase effect.
Also, your entire world will be viewed through shutters, this may cause issues
with
CCFL lamps, street lamps, fluorescent time-multiplexed displays on video
players,
other displays in the same room, etc.. That is the price to pay for 1080p per
eye.
Some 3D has been demonstrated at the IFA, and I'm sure more will be seen at the
CES. And, of course, there will be 3D at The Tech Retreat 2010 ! I'll be there
too,
with a paper about the Philips Cinema 21:9 TV. 2560x1080p.
http://www.hpaonline.com/mc/page.do?sitePageId=99255&orgId=hopa
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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