Head Tilt and 3D TV Glasses

Insight Media’s friend, contributor and colleague Pete Putman, said "Sony 3D TV: Unwatchable!" in his blog published after the recent CEA Line show in New York. Similar problems were remarked upon by Gary Merson in his HDTVGuru.com blog posts less bombastically titled "Sony KDL-55HX800 3D HDTV-First Impressions" and "Compatible 3D Glasses? No Such Thing".

Insight Media’s Chris Chinnock was also at the CEA Line show. Here is what he and other analysts have observed about the Sony 3DTVs and their active shutter glasses:

• With you head perfectly straight, there is very little ghosting - better than the Samsung LCD 3DTVs.
  
  
• Tilt your head to the left and ghosting appears very quickly and the color takes on a definite bluish cast.
  
  
• Tilt your head to the right and ghosting again appears quickly but a reddish tint is observed.

For the Samsung LCD 3DTV, Chris and other observers have said:

• With your head perfect straight up and down, there is some minor ghosting in some content.
  
  
• Tilt your head to the left or right and the ghosting remains similar, but the image gets darker the more your head tilts. At a 90 degree tilt, the image disappears.

While we could see the effects and the differences between Sony and Samsung, we wouldn’t go so far as to call the Sony TV unwatchable. Since Sony doesn’t have the reputation for selling "Unwatchable" televisions and we were interested in getting the story straight from the source, we arranged a conference call with Greg Belloni in Sony PR, Arturo Jordan (Product Planning Manager), and Mike Patton (Sr. Product Manager Bravia).

They explained the basic difference between the Sony and the Samsung active glasses was due to the fact that the Sony glasses have only one polarizer after the LC cell in the shutter. The Samsung glasses have two polarizers, one before and one after the LC cell. In order to get extinction, the Sony glasses rely on the fact that the light coming from the LCD-TV is already polarized.

Sony omits the polarizer before the LC cell for two reasons:
1) To reduce flicker-related problems
2) To increase the total throughput.

The second reason is easy to understand. Even in light with the correct polarization, an absorptive polarizer only transmits about 80% - 85% of the incident light, depending on the exact polarizer specification. Thus the Sony one-polarizer system gains 15% - 20% in throughput and TV brightness compared to the Samsung two-polarizer system.

The first reason is somewhat more difficult to understand. Sony glasses flash at 48Hz per eye when the TV has movie input and 60Hz per eye with normal TV input. Ambient light, especially florescent light but including incandescent light as well, has a strong 120 Hz component in 60Hz countries such as the US or most of Japan and a strong 100Hz component in 50Hz countries. This can set up a beat frequency between the ambient light and the shutter glasses. The 2Hz difference between 48Hz and 50Hz is apparently particularly offensive but the 12Hz beat between 48Hz and 60Hz is also visible. Sony says there is little or no problem with 50Hz TV in Europe or 60Hz TV in the US. No frequency difference means no beat frequency and no flicker.

By eliminating the first polarizer Sony says the unpolarized light that comes through from background sources comes through with the same brightness regardless of whether the glasses are on or off. Since the glasses don’t affect the transmitted light, there is no beat frequency and therefore no problem.

For the Sony one-polarizer system to work, the glasses must remain aligned with the polarization of the screen. This means the viewers must sit up and not lean on a pillow or, heaven forbid, lie down while watching TV. This doesn’t match the viewing habits of many 2D TV watchers, will it match the habits of 3D TV viewers?

Sony says you shouldn’t lie down while watching 3D TV. 3D is based on horizontal parallax. If you lie down, your eyes are now aligned vertically and the eye/brain combination must strain to see the correct 3D image.

In April, the 3D Consortium issued a report on 3D TV viewing issues and ergonomics—in Japanese. Both Insight Media and Sony America are awaiting the official translation of this into English. According to Sony, page 13 of this report recommends that you should not watch 3D TV lying down because it is "easier for the eyes to become fatigued."

But will TV viewers be willing to watch 3D TV only while sitting upright? If you are a viewer where the answer is yes, the Sony system may be for you, especially if you live in a 50Hz country. If you only want a little bit of head tilt, perhaps the Samsung approach would be better for you. The screen will get dimmer but the color and crosstalk will remain unchanged.

If you want to lie down and watch TV, there are two options. First, you could watch your Sony or Samsung LCD-TVs in 2D. Alternatively, you could buy a plasma 3D TV from Panasonic. Since it doesn’t produce polarized light the Panasonic active glasses must use two polarizers. There will be no changes in image quality with head tilt so you can lie down to your heart’s content. Then you only need to worry about eye fatigue but since many TV viewers who lie down fall asleep immediately, this may not be a problem either.

By Matt Brennesholtz, Display Daily