Watching 3D TV: Are glasses required?

Bringing out another dimension from a television has recently become a popular topic.  The question is, how good is the 3D, and how much of a hassle is it to watch? At this point a lot of people have seen 3D in theaters (where they use passive glasses). But will the home experience be the same? Looking at the form of 3D TV, here are a few different technologies that are used for 3D TV effects with varying benefits and drawbacks.

This Christmas season there will be over 2 dozen 3D movie titles available, and some carriers are even starting to provide dedicated 3D channels (DirectTv claims to have 3).So what else is required to view a 3d image.
Stereo picture: This technology shows two images side by side, each from a slightly different angle that is nearly imperceptible at first glance. Glasses with lenses are used to allow a watcher to focus the images into one three dimensional image by tricking the brain. Although a lens is required these glasses can be very inexpensive. Without the glasses both images look fine, but of course having duplicates on a TV means only 50% of the pixel can be used per image. Still, it’s possible to broadcast or view on any television since there is nothing special about the image itself.  Creating content for stereo picture simple involves taking a second image. A crude stereo picture can be created using a single camera but there are also tutorials for creating a dual camera system. The basic principle is simple, mount two cameras about eye distant apart and hook up some device to take a picture (or video) with both at the same time, then display them side by side. Precision control of this style setup is what James Cameron helped invent to film the movie Avatar, although it is not shown in stereo the dual perspective is used in all proper 3d. Stereo Image Sample.

Passive glasses anaglyph: Anaglyph images have been common in the past but are mostly a gimmick. The colored lenses required to properly view anaglyph work as filters. Each eye will only see one of the color layers, and the brain naturally fuses the two. Images like this are fairly easy to create, however to do make it properly two images are still required (one for the perspective of each eye). Instructions on how to alter the images and add the color layers can be found around the web, the same principles can be applied to an entire movie or show. Because the glasses work as a color filter it’s nearly impossible to represent some hues of colors and transitions between two colors are have a vastly different look than those of normal images. Also, color blind people are usually unable to view the 3D as the filter effect is lost.  Anaglyph image sample.

Passive glasses polarized (Currently available for TVs, computers, popular at movie theaters): Polarization is sometimes compared to window blinds where horizontal light waves can fit through horizontal slits and vertical through vertical. This analogy is not accurate for a number of reasons. Not only do light waves not work like that the glasses are circularly polarized, which means the glasses still work even if a viewers head is tilted. With directly horizontal or vertical polarization this would be a problem. With circular polarization the right and left eye will view different images, one polarized counter clockwise, the other clockwise. Projectors or TV’s put out two unique images and the glasses filter them for each eye. This is the technology that is used in many movie theaters because the glasses are relatively inexpensive.

Shake Stereoscopy: The common theme among all 3d technologies is that when two slightly different images are viewed the brain can interpret them as unique perspectives, giving a 3d effect. Shake stereoscopy takes this to a very basic level. Shake stereo will not work in print, only animation, because it flashes each perspective one after the other. In a 24 frame/second video 12 images will correspond to the right eye perspective and 12 will be left eye. By showing every other frame from a different perspective (1Left, 2Right, 3Left, 4Right, etc) shake stereo again tries to trick the brain into thinking it is seeing one image. However because the location of objects and visibility of items can clearly be seen by both eyes, the result is a very shaky image. The 3D does show through somewhat but this option is easily the least effective of the group (except to color blind watchers, where anaglyph may take the title). An example of this is below

Active Shutter Glasses (Currently available in TVs and for computers): The current cutting edge technology, active shutter glasses combine imagery on screen with external devices to deliver a unique image to each eye, again tricking the brain. Active shutter combine the alternating image theory of shake stereoscopy, with the filtering theory of polarization. The video source puts out a signal that refreshes the screen faster than the human eye can detect, only TV’s with high refresh capabilities are candidates but many current market TV’s already refresh at this rate. The glasses then use liquid crystal to block each lens at the same rate, turning one lens black while the other is clear and then switching. A radio signal then synchronizes the lens flickering with the TV refresh so that each eye only views the image from that perspective. Because of all the technology in the glasses and TV this method can become costly with glasses running upwards of $250/pair.

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