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3D without glasses is here – is it really? Yes, of course it is, just look around you! You need no glasses, you just need two eyes to see your world in 3D. This is not what you want to hear? You want so watch movies in 3D without glasses? Well, that’s a little more complicated.

In order to see something in 3D, each of your eyes must receive a slightly different image. This is possible, if the image you look at is made up of columns and each second column is taken from another image than each first column, let’s say the odd columns are taken from the left and the even columns are taken from the right image. The next step necessary is to hide the odd columns from your right eye and the even columns from your left one. The principals known are called “parallax barrier” and “lenticular lenses”. They are applied already for a long time, currently for instance to LCD screens.

But they are far from perfect. The first drawback is obvious: you lose resolution, the resolution in horizontal direction will drop by 50 percent. The second drawback is not so obvious: there are only a few positions in front of the screen where you can view a proper 3D image. The best viewing position is in general in the center opposite of the screen. If you move to one side, let’s say to the right, you will get into a zone where your left eye will not receive any longer the left image, but will get into the light cone of the right image, and vice versa. This will make you see an “inverted” stereo image, a very queer experience.

By moving further away from the center you will get into a zone again where your eyes get the correct images, and everything is fine again. This may repeat a couple of time but in any case, the number of viewing positions with correct stereo image perception is limited. This is the reason why this kind of 3D without glasses is not suited for an audience of more than a few persons.

The “inverted stereo image” problem can be overcome by eye-tracking the viewer. But this requires a camera watching the audience, a computer that evaluates the camera images, and a parallax barrier or lenticular lens array that can be positioned dynamically. This has been shown to work, but only for one or maybe a few viewers.

Another way of displaying 3D without glasses is the so-called light field approach. All you have to do is to reproduce the distribution of light beams around the object that shall be seen in 3D. What sounds so simple in theory is extremely complicated in practice. But it is possible! You need a lot of projectors fed with specially prepared image data, and a large lens array. Nevertheless, the spatial resolution is poor. And the expenses to generate the image data are enormous. If you want to produce a real motion picture you need a whole lot of cameras. A little bit easier is the production of computer animated movies, but the computers will have to generate not only two views of each scene, but tens or even hundreds. In addition, you need a whole lot of image processing computers that generate the data fed to the projectors during replay of the movie – regardless if it is a motion picture or an animated one. The light field approach will work for an unlimited number of viewers – as long as they are satisfied with a resolution a lot lower that that of an LCD screen. So, is glasses-free 3D really here? Yes, it is but the 3D experience is not so impressive yet, especially for more than one viewer at a time and nobody can tell us currently when this situation will substantially improve