# An In-Depth Look at 3-D

## Article excerpt

Three-dimensional images--once limited to special movies and View-Masters--are now commonplace. Many movies at the theater are shown in 3-D, and video games, DVDs, and televisions all offer 3-D, as well. Providing a perception of depth adds a sense of realism for the viewer. How, exactly, do we perceive three dimensions in real life, and how is that different from "seeing" three dimensions when looking at a flat screen?

There are several important visual clues that help us to perceive depth. One example is our experience with the relationship between size and distance. A second has to do with the fact that foreground objects may block some part of objects in the background, which is known as obscuration--a tree growing in front of a house blocks part of the house. Nonetheless, humans perceive three dimensions primarily because of binocular vision (Howard and Rogers 1996). Binocular vision means that each of two separate eyes sees a somewhat different image that is fused into one by the brain. (Martin 2009). Binocular vision may lead to stereopsis, where the different images (each one shifted slightly to the right or left) seen by each eye are interpreted by the brain as depth. You can easily see how this works by placing a dot on a piece of paper and placing it within reach. Then, with one eye closed, try to quickly bring your finger from eye level straight down on top of the dot. You likely will miss the first time you try this. Why? Hold your finger at arm's length and view with one eye. Now view with the other eye and note that, with respect to the background, the finger seems to move right or left. This is because of your binocular vision--each eye sees your finger from a slightly different horizontal position. Your brain interprets these two images and is able to perceive the third dimension, depth.

The engineering challenge for creating 3-D images is to devise systems in two dimensions (movie screens, televisions, etc.) that produce images that seem to be three dimensional. To do this, a slightly different image must be shown to each eye, mimicking what occurs in stereopsis when we view the three-dimensional world. In this activity, students will investigate several different designs that enable the viewer to perceive 3-D images. The International Technology Education Association states that middle-level students should learn that "innovation is the process of modifying an existing product or system to improve it" (2007, p. 110). In a similar way, the Framework for K-12 Science Education notes that "engineering design is both iterative and systematic. It is iterative in that each new version of the design is tested and then modified, based on what has been learned up to that point" (NRC 2012, p. 46). Methods for producing 3-D images have evolved using several techniques since their beginning in the 1840s. The science content of this lesson avails itself to inclusion in a unit on information processing (LS1.D from A Framework for K-12 Science Education): "Each sense receptor responds to different inputs (electromagnetic, mechanical, chemical), transmitting them as signals that travel along nerve cells to the brain" (NRC 2012, p.149).

Historical information

Three-dimensional images have been around longer than you may think. The world's first photograph, actually known as a heliograph (literally, sun writing) was taken in 1826 by Joseph Nicephore Niepce in France using an hours-long exposure time (National Geographic). By 1838, Charles Wheatstone had developed the idea for stereo photography. He constructed the first device that allowed each eye to see a slightly different view of the same image. His idea, which used mirrors and prisms, was later simplified, and by the turn of the century, most homes had a stereoscope and a collection of cards for viewing (see Figure 1).

Motion pictures were developed in the later part of the 19th century. Thomas Edison perfected a viewer called a kinetoscope, which was a machine used to view a moving strip of still photographs that gave the illusion of motion (National Park Service 2012). …

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