the viewer’s left eye only sees the left image while the right eye only sees the right image, the brain will instantly fuse the images into a 3-D scene.
This is exactly the way we see our actual environment, so the effect isn’t too surprising. Many nineteenth-century families owned stereoscopes based on Wheatstone’s principle, and the devices became the first medium for mass-market photojournalism, exposing millions of middle-class people to 3-D pictures of exotic places they’d never get to see in person. I’ve made a hobby of collecting the old stereograph cards produced for the devices—see my December 2008 column “The 3-D Graphics Revolution of 1859.”
Stereoscopes went out of fashion by the 1930s, but the same principle popped up again in the 3-D films of the early 1950s. Just as before, the creators of 3-D monster features like House of Wax (1953) used special cameras to capture a stereo pair of images for each frame of the film. But whereas the old stereoscopes used a physical barrier, typically a slat of wood, to keep the left eye from seeing the right image, and vice versa, early 3-D films were based on “anaglyph” technology. Here, the two images were filtered through glasses with differently colored lenses, typically red and green. A similar system is still used today for films like James Cameron’s Avatar, except that modern 3-D glasses filter the left and right images using polarized lenses.
The first age of 3-D photography, then, had two defining characteristics. First, it was only possible to create 3-D images using specialized, expensive equipment. (The main exception was the Stereo Realist, a consumer-oriented stereo camera produced by the David White Company of Milwaukee, WI, from 1947 to 1972. It created color slides that could be viewed using a View-Master-style device. President Dwight D. Eisenhower was one famous Stereo Realist devotee.) Second, it was only possible to experience stereoscopic 3-D images using a variety of kludgy, uncomfortable systems designed to prevent interference between the left and right images.
In the new second age of 3-D photography, both of those requirements have gone out the window. With Lytro’s technology, you don’t need to capture a pair of images in order to recreate a scene in 3-D, and you don’t need a special stereoscope or glasses to explore the subject in 3-D. You do, of course, need a computing device that can render an image interactively.
I won’t try to explain light field photography in detail (I couldn’t anyway—we’re talking advanced optics and image processing here) but the general idea is this: in a traditional digital camera, a lot of data goes to waste. Light is coming at the sensor from everywhere, but at each point on the imaging plane, the sensor only records the aggregate intensity of this light in the red, green, and blue parts of the spectrum. All information about the direction the light rays came from is lost.
In Lytro’s camera, there’s a microlens array that divides the sensor into thousands of mini-cameras, each of which captures a scene from a slightly different angle. In this way, information about the directionality of the rays is preserved.
The result isn’t a conventional image at all, but rather a few megabytes of data representing a “4-D light field.” This field can be sliced and diced in a variety of ways using software. One way is to change the plane of focus in the image—in effect, isolating one 2-D slice of the 4-D light field. Another way is to pivot between different virtual points of view. That’s Perspective Shift.
Cheng admits that it’s a challenge to explain the physics of light field photography to lay people. But they don’t need to grok the details in order to grasp what’s going on with Perspective Shift. “When people see it, they immediately understand,” Cheng says. “It’s a little bit like magic—they don’t care how it’s done.”
Now, there’s still a big difference between exploring a subject in 3-D—that is, being able to rotate the perspective back and forth a bit—and actually seeing it in 3-D. Cheng says that as soon as Lytro released the Perspective Shift software upgrade, customers began
