[opendtv] Re: 1080p questions

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 7 Dec 2009 09:06:14 -0500

Jeroen,

Thank you for the richly detailed course on the state of 3D cinema!  I now have 
a lot of Googling to do.

However, my original question was a bit simpler.  I wondered what would happen 
if you tried to use LCD shutter glasses with existing displays, as you 
originally proposed.

I have two LCD displays in my home.  When I wear polarized sunglasses and view 
my LCD television, the image is blocked out if I tilt my head 45 degrees to the 
right (from my perspective), and fully bright if I tilt my head 45 degrees to 
the left.  My other LCD display behaves in the opposite manner.  when I tilt my 
head 45 degrees to the left, the image is blocked out.

Obviously both LCD manufacturers made their displays with the final polarizer 
on a 45 degree bias to horizontal in order to minimize the blocking effect of 
someone viewing while wearing polarized sunglasses (which are vertically 
polarized.)  I've also noticed this same effect on gas pumps with LCD displays, 
and with in-car navigation screen displays.

So my question was what effect wearing LCD shutter glasses would have on the 
viewing experience.  If the glasses had their final polarization lenses on the 
same bias as the LCD television, then when the glasses were in the "clear" mode 
all of the light would get through.  However, this same bias on another 
television might block all light!

So the only way to make glasses compatible with all LCD televisions is to have 
the final polarization either vertical or horizontal, guaranteeing that 
everybody will see the image, but also that everybody will experience reduced 
brightness and contrast, unless they cock their head like a Collie hearing her 
master speak.

John
  ----- Original Message ----- 
  From: Stessen, Jeroen 
  To: opendtv@xxxxxxxxxxxxx 
  Sent: Monday, December 07, 2009 3:14 AM
  Subject: [opendtv] Re: 1080p questions


  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. 



  ...snip...



  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. 

   

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