The Renaissance of 3D:
How the New 3D Technologies Work
LCD shutter glasses are the first high-quality 3D implementation suitable for home use. In systems that use these glasses, the video display shows alternating left-right images very rapidly--up to 120 frames per second. The viewer wears a pair of active LCD shutter glasses which alternately block the left or right eye. Much like the effect of a DLP color wheel, this happens so quickly that your brain melds the two images together and creates the impression of a single image with 3D depth.
Advantages of Shutter Glasses
Color. While glasses vary, most have lenses without significant tint, which puts them on par with the polarization method for color accuracy. The glasses we have been using have a greenish tint to them but other brands we have seen do not.
Cross-talk. LCD glasses are perhaps the best of the bunch when it comes to cross-talk because the eye not being used is actively blocked by the shutter mechanism. Earlier versions had problems with ghosting, where part of the previous image would be retained on the screen after a new image had appeared. Newer, faster displays have all but eliminated this artifact.
Relatively inexpensive. The prices of 3D projectors and televisions are already very low. Even today, a projector capable of 3D at 720p is available for less than $800. While there are ancillary costs involved, such as a computer with a powerful graphics card and a set of glasses for each viewer, for home use with small audiences it is certainly affordable.
Disadvantages of Shutter Glasses
Active glasses. This is the main difference between LCD shutter glasses and other systems: the mechanism that controls which eye sees what is embedded in the glasses, not the content or the projector. LCD shutter glasses are great for small audiences of responsible adults, but they have several downsides. They are expensive compared to the cost of glasses for all other technologies ($100 to $150 per pair at the time of this article's publication). They are complex, with batteries and electronics and fragile LCD lenses. If they are dropped, stepped on, or run out of batteries, it can disrupt the 3D experience. And if you have a lot of friends who want to come see the Super Bowl in 3D, it can be costly to supply everyone with their own pair.
Synchronization. An active shutter system needs to have a way to synchronize the shuttering of the glasses with the content on the screen. Some systems use an infrared emitter. Texas Instruments' system for projectors and televisions, called DLP Link, uses synchronization pulses built into the projected image itself. While the two implementations use different sources for the pulse information, the pulses themselves are the same.
There is a difference between a left-eye pulse and a right-eye pulse, which is why all glasses synchronized with a given TV will be in synch with each other as well. But the projector has no way of knowing which frame is intended for which eye, leading to an interesting problem. These pulses can become reversed, leading to one eye seeing what is intended for the other. In other words the left-eye pulse will be associated with the right-eye image. This is known as the "pseudoscopic effect" and it is quite disconcerting the first few times you experience it. The effect is a strange sense of the image being inside-out, as if you are looking at a hollow 3D image from the wrong side. It is a common occurrence, so manufacturers have planned for it - it can be remedied by toggling an option in the display, or a computer's video card driver, or sometimes in the software itself. Still, it is not as foolproof as other systems.
Flicker. Some people have reported seeing flicker when using shutter glasses. Flicker is what happens when the refresh rate is not high enough, leading to a sort of stop-motion effect. It is true that, since each eye only receives half of the refresh rate, projectors used with shutter glasses must be very fast. To this end, modern implementations use at least a 120Hz refresh rate to deliver 60 frames per second per eye. We did not encounter any flicker during our testing so we cannot comment on the phenomenon's prevalence or seriousness.
Light loss. Shutter glasses systems use a single projector which switches rapidly to display different images, so there is a minimum 50% reduction in light output compared to 2D just as in other single-projector systems. The glasses reduce perceived brightness as well. While not all glasses are the same, the models we have tested decrease perceived brightness by roughly 60% regardless of the display or the content. The upside is that they also reduce black levels and contrast is increased significantly.
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