3DTV without glasses?

The question of glasses required to watch 3DTV has been a recurring one for quite some time and it still seem to bother some people.

One thing that is fundamental in understanding the issue is that the current generation of 3D (on television but also in theatre) is not the same 3D as you perceive it in real life.

In real life the objects are actually there, existing in 3D in front of you. Therefore, to perceive it, your eyes and brain use different mechanism. Stereoscopic perception (based on the different angle that your two eye perceived) is one important one but there are a number of monocular cues that we use as well: motion, perspective, focus, shadows and occlusion  to name a few (for more detail see the article on Wikipedia).

However, when we look at a 3D picture on TV or in theater, we see two 2D picture with containing some difference intended for your right and left eye in order to trick your brain in thinking the objects do exist in space and are at different depths. So stereoscopic 3D as we call it is an effect basically. Only part of our of our depth perception mechanism are utilized to perceive it. As a result, it is fairly complex to produce good stereoscopic content because different condition of production, different distance, different lens can create a 3D effect that can look believe but also can look not believable at all. Most people will actually not be able to point out what is wrong with a bad stereo 3D picture but they’ll see that something is wrong and that it doesn’t look natural or gives them headaches.

So back to the glasses… because stereo 3D is an effect done with two 2D pictures, there needs to be a mechanism to send those two pictures to your eye independently. At this point, there are three main ways to do that:

  • Active glasses: That is still the most common type of 3DTV sold today. The principle is to present to you the pictures on the TV at an higher refresh rate. For instance, the TV can present 120 images per second for content at 60 images per second. For 1/120th the left eye picture is shown followed by the right eye one in the next 1/120 of a second. The active glasses that you wear are in fact LCD screen that can let the picture past though (when it is the correct picture for that eye) or block the picture when it is destined to the other eye. Some theatre system use active glasses but it’s a small amount.
  • Passive glasses: Those type of TV were fairly expensive at the beginning but the manufacturing process did evolved and it is now as cheap and sometimes cheaper than the active type. Those TV are rapidly gaining market share and it use the same principle as the most commons type of 3D in theaters (such as RealD). The principle is based on polarization with some pixels sent with a light polarity to the left eye and some with a different polarity to the right eye (for more detail see Wikipedia).
  • Autostereoscopic: This is the kind of TV without glasses. Now it still need to send a left eye and right eye picture to your eyes. In order to do that without glasses, it uses small lenses in front of the screen that focus the light of each pixel in specific direction. This is tricky because it requires that the viewer find a “sweet spot” by moving right and left to places where his eye will receive different pictures. If the device is a single user device like Nintendo DS or a phone, this is not a big issue since the two picture and destined to a single viewer and it is easy to adjust the device to your vision. However, if it is a large screen and many people can watch it, then we need to create more angle so that those people can all enjoy the 3D. For that reason (for large screen) he more angle the better. Some good auto stereoscopic displays used in exposition or stores have as much as 19 different views. The problem is that for each view, you need to dedicate pixels and so for 19 views, the screen resolution will be divided by 19. That’s good to create a show stopper effect but not so much to experience high-quality content in your living room (not to mention that any text becomes unreadable).

Now that we have looked at the three main types of displays, we can put things a bit in perspective. Because of the fact that you need to divide the resolution by the number of view, autostereoscopic display will remain not practical for a good 3D experience at home for many years. The resolution of screen will need to become significantly higher to make it a good alternative. Glasses have bothered some people but I think that is is especially true of the active type of glasses which are bulky, create a perceivable flicker and requires to be charged. The passive glasses are light (in fact with LG screens you can use the RealD glasses from theater and it looks better!), have no flicker, do not need to be charged ever and are cheap.

One thing to note is that most passive glasses TV do cut the resolution in half vertically. I don’t think that this is an issue at all in fact. All content that you can watch in HD today is compressed by a large factor and loose more resolution than that. While it will be even better at full resolution, I don’t think that anyone will notice a resolution difference on actual content.

On the other hand, the autostereoscopic displays, not only have years to go on the scene resolution side to achieve a good image quality, it also will create artifacts from the multi views perspectives. In my example of the 19 views screen, not only do I need to have content that have been created in 3D, I need to have a different angle created for each of the 19 angles! Since no movies are created that way, I need to take the stereo pictures and extrapolate the 19 angles. There are some techniques to do that (including creating or using a depth map) but it will create unintended artifacts. So, autostereoscopic displays for game consoles, phones and tablets, yes; For TV in your living room not before 5-10 years at least!

I think that anyone (anyone with stereoscopic vision that is) that gives a real shot at a good passive glasses system (like the LG Cinema series) with good 3D content will not be bother by the glasses and will benefit from a great experience.

Let me know what you think!

2 Comments Add yours

  1. laurent.daudelin@gmail.com says:

    Well, I have just got my first HDTV last year and having worn eyeglasses since 3rd grade, I’m not interested in having to wear glasses to watch the television. So, I will pass the glasses-based ones and will wait for the latter model to gain traction.

    Thanks for the great explanation!

  2. Hi Stephane, I found your article very interesting and you are right for most undeveloped 3D Auto-stereoscopic technologies being trialled. We have been developing this technology for around 25yrs and we are now ready for it to enter the Home End User Market.
    The most interesting thing is most people are unaware of how far this technology has actually come. I look forward to the market-place reaction when we launch this year to end users.
    We are launching our renovated website on Feb 1, I would like to invite you to join our VIP section as we will be running forums and seeking out different 3D content from around the World. We also have a Webstore with different departments for you to browse. I look forward to seeing you at our forums in February

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