Because my brain assumes its size hasn’t changed and I know roughly how big it is, that’s one cue about its distance. For example, a close-up object occupies more of your field of view and gets smaller moving away.
It’s not a daily issue because there are many depth cues. Some people are stereoblind - they can’t triangulate between their eyes.
This, combined with the glasses, sends images in rapid alternation to the eyes. A device in front of one project flips rapidly between the two forms of circular polarization. Circular polarization avoids this problem. Your brain merges the images to see depth.īut tilting your head puts the filter at the wrong angle - each eye may start seeing a weak version of the other’s image. The 3-D glasses have polarizing filters matching to the projectors’ filters. Light from one projector is polarized in one direction and light from the other is polarized along the perpendicular direction. One projector displays images intended for the left eye, and the other for the right, with a polarizing filter in front of each projector. They align two projectors so images line up on the screen. Digital IMAX theaters use linear polarization. Theaters use two forms of polarization for 3-D movies - linear and circular. Humans aren’t sensitive to light polarization, so image quality isn’t disrupted. That plane - the wave’s orientation - is what we refer to as polarization. Light is an electromagnetic wave traveling along a particular plane. Nowadays, we avoid this problem by using glasses that work with polarization. However, this system depends on color filtering that distorts the movie’s color quality. Shifting in the opposite direction pushes the image back. Increasing the offset a little, so the left eye’s image goes to the right and the right eye’s image goes to the left, pulls the image out in front of the screen. By drawing the images on top of each other, viewers will see a flat image on screen (the offset between the eyes is zero). Geological Survey - Geology Discipline / Public domain.įilmmakers consider how the degree of offset between these images translates to depth inside our brains. The lenses control what each eye sees by filtering the light going to each eye, only letting certain wavelengths pass. With the glasses back on, your brain merges those images to create the perception of depth.
Look at a movie character without the glasses - two outlines extend from the character, identical except one’s blue, the other red, and they’re slightly offset. They approximate the offsets, depending on how far things are, that your eyes expect in life. The glasses recreate that triangulation by feeding distinct images to the eyes.
Scientists think that computation occurs in the visual cortex, where individual brain cells seem sensitive to specific distances between the eyes and use those distances to compute depth. Your brain uses the offset in those views to determine an object’s distance, triangulating between both eyes. Hold a finger in front of your face while covering one eye at a time - the position of your finger jumps. We see the world from two, shifted views, one provided by each eye. How do the “classic” 3-D glasses with the red-blue lenses work?
Jenny Read, a vision scientist at Newcastle University explains how filmmakers use the brain’s natural functioning to create the 3-D experience. Most of the technology making 3-D movies work exists inside our skulls. With 3-D glasses, explosions, gore, or magical creatures jump off the screen.