A presentation by Stephanie Zeil

Overview  The viewing of objects in (or as if in) 3D is referred to as stereoscopy.  Techniques involved include use of stereoscopes anaglyphic polarized light shutter glasses the Pulfrich effect autostereo systems (any system without glasses/headgear) Since anaglyphic, polarized light, and shutter glasses systems are the most common stereoscopic systems in use regarding film/TV, we’ll focus on those.

Overview  Stereoscopic techniques create the illusion of 3D by taking two images with a slight disparity and fusing them into one.  This simulates how our eyes perceive the world. While both eyes converge on an object to focus, the images we receive are at slightly different angles due to the space between our eyes.

To better demonstrate, here is a “jiggly gif” of the Crab Nebula. As the picture moves back and forth, it is actually switching between two pictures– one for each eye. Since the movement is slow and both eyes can see both images, the effect is harder to notice, but you may still perceive the image as having depth. This is similar to how the 3D effect is accomplished using shutter glasses.

Time Sequential Stereo Shutter Glasses The images displayed quickly switch between what the left and right eye are supposed to see. At the same time, the glasses alternate having one lens covered or darkened so that only the eye corresponding to the image receives it.

Time Sequential Stereo Shutter Glasses The glasses used can be mechanical or liquid crystal. Mechanical shutter glasses feature a rotating disk with opaque and transparent sections to alternately cover and expose the eye. Most shutter glasses today use liquid crystal, which darkens in response to electrical signals and then lightens in their absence.

Polarized Light Two images are projected onto the screen; each is polarized differently. The glasses worn have a different polarization filter in each lens– one lets in only the first type of polarized light (and the other lets in the second.) The viewer receives a different image in each eye but only sees one 3D image.

Polarized Light Linearly polarized light systems carry the disadvantage that if the viewer tilts their head the axis of transmission also moves and the images are not properly filtered. Any system utilizing polarized light requires the projection screen to preserve the projected light’s polarization. The “silver screen” we associate with the movies has won itself a comeback. Metalized/silvered screens are used for polarized 3D films. Circularly polarized light systems polarize light so it moves in clockwise or counterclockwise helixes so this is not a problem.

Anaglyphy Probably the most well-known 3D viewing method, the glasses’ lenses are near- complementary colors (colors opposite each other.) Each lens only accepts a certain spectrum of color. By using complementary colors, one lens accepts what the other does not, and vice versa. Like the other systems, this ultimately means the two eyes receive different images but the viewer sees one 3D image.

Anaglyphy Unfortunately, using color filtering means that the colors of the image may suffer. Different combinations of colored lenses may be used depending on what is deigned most important. For example, classic red and blue is best used to avoid “ghosting” of the image, but the colors appear washed out. Red and cyan, on the other hand, leaves some ghosting but better preserves colors.

Other 3D Methods  Pulfrich Effect When incoming light to one eye is reduced, that eye detects things more slowly. This creates a slight lag time behind the normal eye when watching an object move horizontally. Having to process these two different images, the object appears to move in and out of the plane as it moves horizontally back and forth.  Stereoscopes An old method of 3D viewing, the viewer looks through the lenses of a stereoscope (pictured below) at two side- by-side images, each representing what one eye sees. This is the same old story; the two images fuse to create one image which appears 3D.

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