Wide Angle 3D Screens

Glasses-free 3D screens normally have to be viewed from a specific angle. Now a team from HP Labs have overcome this problem for mobiles...
21 March 2013

Interview with 

David Fattal, HP Labs


3D screens in TVs and portable game consoles like Nintendo 3DSs have been around for quite a while, but they are limited because you have to watch them from a fixed position.  But, if you don't want to sit around with 3D glasses on, your options are really quite limited.  Now, a team from HP's research labs think that they might have solved the problem. Chris Smith and Dave Ansell were joined by one of the team, David Fattal, to find out more

Dave - So David, how do current 3D displays work?

David - There's a whole set of solutions for 3D display out there, already in the commercial markets and the most common type is the so-called lenticular array.  So, imagine you have just a normal TV and you put a sheet of optical lenses in front of it. So, optical lens is pretty much the same thing that you put in your contact lens that work to refocus light. And what these lenses are able to do is that they're actually sending light from different pixels on your normal TV into different directions of space. So, they create a bunch of direction of light rays and when a viewer actually looks at the 3D display, a different image is going to come to his or her right and left eye, and therefore, they're going to perceive these so-called 3D stereoscopic effects. So the brain sees slightly different images and re-constructs the depth information about the image.

Chris - Because the key thing is that you've got to send a different picture to each of the two eyes for the brain to then recombine those and create the 3-dimensional effect, haven't you?

David - Yes, so this is exactly correct. People have been traditionally trying to 3D gogglesdo that using glasses. So glasses artificially block one image or another, in front of your right or left eye. But the trick here is to try to do this without glasses so that your display might be able to send different images in different region of space to reach each one of your eyes.

Chris - Now of course, the problem with doing this is that the computer or the display doesn't know where your head is and therefore, doesn't know which bit to send to which eye. So, how have you got around that problem?

David - Yeah, this is a great question. So eventually, you're right. The display doesn't know where you're located and so we take the brute force approach where the display actually sends all possible perspectives, all possible images of the 3D objects simultaneously in parallel in space. So that any viewer, not only one, but you can have 10 viewers at different position around the display and each one of the viewers would have a different imagery to right or left eye, so they would all be able to see simultaneously in 3D.  so again, a brute force approach just send all the images at once.

Dave - I guess that has the advantage also that if you move your head, you'll see around the object in the TV as well.

David - Exactly. So, this is one of the really important points about our technology is that, you can actually move around objects and very much like you could move around the hologram of Princess Leia in Star Wars that people like to reference.

Chris - David, can you talk us through then, how you've achieved this clever trick? So, just take us from the bottom up of a normal screen with its pixels and things. How do you get the effect you're achieving?

David - So our technology is very similar to liquid crystal display technology that is mainstream today in cell phones and in your laptop screen, and the way these displays work is they have two parts. The first part is called the backlight and the role of the backlight is so you basically illuminate from the sides with a bunch of lamps, they're called LEDs. And so, the light propagates from the side of your backlight which is a big piece of glass or plastic, and as it propagates from the edge to the centre, it encounters a bunch of so called scatterers so imagine a bunch of little bumps on the surface of the backlight. And when light encounters such a bump, it actually scattered from inside the backlight into the viewing zone of the display outside. So, this scenario is a constant flow of light and in order to form an image, you need a so-called modulator and this is usually done using a liquid crystal front display which is imaging a bunch of little cells that can be controlled from completely transparent to completely opaque by just applying a certain voltage.

Chris - So, how do you then get the light so that it's only going in a certain direction. So in other words, if you were looking at it straight at the screen, one eye is going to get information from one pixel area and another eye is going to get a different one. How do you control the direction of the light?

David - Yeah and this is where our invention comes from. We replace the little bumps I talked about that are present in traditional displays, we'll replace them by nano structure which are called diffraction gratings which are objects with features that are smaller than the wavelength and when light hits each of these objects, or these diffraction grating, it is scattered in a very directional manner. So, it forms a light ray and in one particular direction. And then by changing the exact parameters of this nano structure, we are able to control the direction at will. So, we can create any light ray, we can send an image in any direction we want and in parallel.

Chris - So, can you change the direction that that grid is sending light in or is it fixed?

David - The directions are fixed, so they're set once and for all, and then the external modulator, your liquid crystal modulator is able to change the intensity of these light rays.

Chris - So basically, the computer is working out when to turn the light on or off and it's directing light out of that particular pixel in a certain direction to effectively, an eye or the other eye. And in that way, you can get the two eyes seeing different amounts of light at the same time and that enables the brain to be fooled into thinking it's seeing 3D.

David - Yeah, absolutely and it can do so regardless of the position. And you could even be traveling around the display and you would see a continuous update of the perspective so you would seem like you actually are perceiving a continuous motion of the object in 3D.

Chris - So, how long until I can buy a fancy smartphone and see pictures of my children in 3 dimensions on the screen?

David - You know, as a researcher, I'm not really able to comment on this kind of commercial prediction, but certainly, as a 3D display lover, I would want to see it as soon as possible. So we're just going to work hard so that within a couple of years, we can see the first application one way or another.


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