To display 60hz stereo images, you need a 120hz image and synchronized shutter glasses. Each frame is shown twice, once to the left eye and once to the right. These are interleaved in time and synchronized with the shutters on the glasses that alternately close the left and right eye. To display stereo images, you not only need a 120hz display device, you also need a way to synchronize the glasses with the image. There are some methods that patch into the video stream and use the vsync there, there are some that plug into the television itself and are triggered by actual frame changes. Note that progressive scan LCDs tend to be terrible for stereo, because not all of the image updates at once, and thus each eye sees some of the image meant for the other eye (and you get blurring and the stereo illusion breaks).

I watched a 3d movie on a lcd screen that's not 120 hz (it's less but i'm not sure what hz it was). I saw the 3d image, but it was horrible. It was not pleasing to watch at all. I'm guessing this was due to the "each eye sees some of the image meant for the other eye" idea you pointed out. So this is what 3d tv's are meant to do...improve 3d viewing capabilities, not necessarily create it?

Watching 30fps stereo on a DLP projector running at 60hz is a pleasure. It's not so much the framerate as the fact that an LCD screen does not update the entire image at once, but scans through it one line at a time. This way you don't have a single time point where the entire image is just left or just right. Updating the entire screen at once, at 120fps, is what 3d televisions (and DLP projectors) do, in addition to providing an external sync trigger signal for shutter glasses to latch onto. That is what makes a display device 3d compatible, not the frame rate in itself.

That said, if you have a high enough framerate on an LCD you can simulate the global screen change effect by just showing each frame longer, for example running a 120hz screen at 30fps stereo (60 fps total), and showing each frame twice, giving the screen time to update.

Not exactly.

For a computer monitor to be compatible with Nvidia's 3D shutter glasses, all it needs is for it to be 120Hz. The connected computer has a USB dongle which the 3D glasses sync with. For a TV to really 3D capable, it has to have the dongle built in, and be able to interpret a 3D signal (HDMI 1.4a[1]). What confuses the issue is that most TV's and computer monitors these days have both HDMI and DVI ports on them.

[1] http://www.hdmi.org/press/press_release.aspx?prid=120

Do you mind if I side-track a little and ask people's opinion of 3D in general?

I've seen two movies in 3D in the past year - Avatar and Toy Story 3. While Avatar was fun, and Toy Story 3 exception, I didn't feel that the 3D really added much to the experience. In particular, the colour for Toy Story 3 seemed dimmer than normal. I also where glasses, so I sometimes had reflections obscuring the picture.

I understand that 3D is being hyped as the next big thing to get after a big flatscreen TV, so I'd be interested to hear what people here think of it.

I've seen 3 movies in 3D. With Avatar and How To Train Your Dragon, I felt the 3D added something worthwhile to the experience. With Alice In Wonderland, it didn't.

I don't think I'd want a 3D TV though, not while you need special glasses to see the picture properly. It's one thing wearing them when you've made the effort to go to the cinema, quite another when you're just casually watching at home; they become something else to lose, like the remote only not as useful.

Also I think 3D glasses would mean no proper TV to people who have spectacles.

I don't generally like it. It's technically neat, and it's fun to see in effect for the "wow" factor, but I don't like it over traditional 2D.

I wonder how much of that is me just having watched normal TV for twenty-some-odd years and how much of it is due the fact that the art of film making has been developed entirely in the context of 2D storytelling.

120 Hz is ambiguous. Are you referring to the display refresh speed? Was the discussion in the context of a specific physical display technology?

Is my 600 hz Plasma 3d Ready?