Seeing is Believing: What is Stereoscopic Technology?

It's common knowledge that we live in a three dimensional world. We can discern objects in terms of height, width, and depth. However, how is this possible? A single eye can only provide a two dimensional image, much like a camera does. Take a simple picture of some fried chicken, for example. With only two dimensional information, it's difficult to see the fried chicken "popping out" as real chicken sitting in front of us would. But when we provide our brains with a few extra points of view (as shown using an animated picture), it suddenly appears to take on tangibility in three dimensions. How does this work?

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Fig 1: Simple 2D image (above) and 3D image using "wiggle" stereoscopy (below).

It turns out that the key to getting the full, 3D snapshot of that delicious looking chicken is having two, separate eyes. Each eye provides its own height and width information, and the brain combines and processes the two images, recognizing and matching shapes and patterns together to provide the third dimension of vision, depth. This process is called stereopsis, stemming from the Greek words for "solid" and "sight."

Mathematically speaking, this is a problem of degrees of freedom. While we desire three degrees of freedom worth of spatial information (height, width, and depth), each image provides only two degrees of freedom (height and width). However, by matching the same spatial point on the two slightly different images, we can close the degree of freedom gap and calculate depth, using the trigonometric relationship between the cameras and that point. But what are the applications of this knowledge?

Fig 2: Example video with accompanying depth map.

With knowledge of how stereopsis works, we can use technology to give ourselves the illusion of a 3D object by projecting a different image to each of our eyes. This is called stereoscopy, from the Greek for "solid" (again) and "to see." Most stereoscopic illusions are constructed for entertainment purposes. The earliest example of stereoscopic technology was the 1849 Brewster stereoscope, as pictured.

Fig 3: Brewster stereoscope.

Sir David Brewster was a Scottish physicist, mathematician, and inventor, among other things. He not only invented the stereoscope pictured, but also the kaleidoscope, which is a common toy even today. The Brewster stereoscope used lenses as shown to help the user perceive a photograph on the left and another on the right as a single, 3D image. Much later, during the 1960's, the first random dot stereogram was made. The random dot stereogram is a single, 2D image that accomplishes the same illusion as the stereoscope when focused on in a certain way (I personally have never found any success with these, but they definitely do work for some people!). Moving further on in time, the early 2000's enjoyed a fad of anaglyph 3D movies (Spy Kids 3D, anyone?). These revolved around the usage of red-cyan tinted glasses in the movie theatre to see two different images from the same video on screen.

Fig 4: An anaglyph stereoscopic image.

Fig 5: How an anaglyph 3D movie works.

However, despite these cool applications, the most revolutionary stereoscope technology has come very recently. In 2009, the science fiction film Avatar premiered the widespread use of RealD 3D. Instead of using red and cyan tinted cellophane, RealD 3D movies utilize circularly polarized image projections, clockwise for one eye and counter-clockwise for the other. This technology was received very well, and since then, many blockbuster major film releases have had an accompanying "3D release." The year after Avatar in 2010, Nintendo's portable gaming system called the 3DS was announced. Unlike any of the devices already described, the 3DS requires no apparatus or special technique whatsoever for proper viewing of the 3D effect. Instead of using lenses to project two different images to each eye, it instead uses what is called a "parallax barrier" to separate the images. The apparatus is shown. It operates by using tiny, periodic gaps in a barrier in front of the actual LCD screen to isolate each eye's image.

Fig 6: How a parallax barrier works.

And the last piece of stereoscope technology I'll mention today is the future of virtual reality. Virtual reality (VR) is an upcoming field that has many applications, even past pure entertainment. It operates essentially in the same way as the original Brewster stereoscope, using a viewing apparatus with two wholly separate images for each eye. However, now not only can we project a video instead of just an image, but we can also update the video in accordance with inertial measurements. This results in the illusion of not just seeing something in 3D, but being inside a different world entirely! This has obvious implications for the gaming industry (jumping into a game, on a whole new level), but its potential powers stretch past that.

Fig 7: Oculus Rift gaming headset advertisement.

While the most development this technology has seen is once again in entertainment, further applications of virtual reality are already being discussed. For one, healthcare is a crucial field where VR could really take off. As reported by TechCrunch, with the recent advent of affordable head-mounted VR devices (like the Oculus Rift, or HTC Vive), VR for surgical training is becoming an increasingly attractive option for professional healthcare trainees. Just as pilots-in-training use aircraft simulators for hundreds of hours before actually stepping into a cockpit, surgeons too could practice their procedures many times before they perform on a real patient. Outside of medical training, VR could have uses in the actual healing process. VR immersion has already been used as a method for pain and stress distraction for patients with issues like PTSD or painful treatments, and applications in correcting vision disorders like lazy eye or cross eyes are also being explored. While this medical side to VR technology is still in its infancy, it could prove to be incredibly useful in the near future.

As for how stereoscope technology pertains to our bee research lab, we’re using the technique in a slightly different way than usual. Instead of using stereoscopic technology to just display 3D videos, we’re using it to capture and analyze 3D videos of bees visiting flowers. The core difference is that we are no longer projecting the images to ourselves and leaving the image processing to our brains. Now, we’re sending the images to a computer, programming that computer to mimic how our brain processes vision information, and using the camera-computer system repeatedly to capture as much 3D bee path data as we want, whenever we want. This way, we can overcome human limits of observation and measurement (it’s difficult to produce accurate three dimensional path data for hours at a time…), and open up frontiers for biological observation. Potentially, with enough passive observation, the data could reveal pollinator interactions and behaviors that would be otherwise difficult to find!

And that's the state of stereoscopic technology up to today, as well as a brief overview of our goal this summer! Feel free to share a comment or ask a question below, and I’ll be sure to reply.

Further Reading:
Virtual Reality for All, Finally (Scientific American)
Virtual Reality Gets Real (Popular Science)
Virtual Reality Treadmill a High-Tech Help for Patients (Cleveland Clinic)

Media Credits:

[1]: Public domain image. http://cdn.deccanchronicle.com/sites/default/files/Wigglegram%20(13).gif

[2]: Video by Stereolabs. https://www.youtube.com/watch?v=_tRDuAZpKMc

[3]: Public domain image. https://en.wikipedia.org/wiki/File:PSM_V21_D055_The_brewster_stereoscope_1849.jpg

[4]: Public domain image. https://commons.wikimedia.org/wiki/File:Persepolis_(By_Abdolazim_Hasseli).jpg

[5]: Photo by HowStuffWorks. http://science.howstuffworks.com/3-d-glasses2.htm

[6]: Public domain image. https://commons.wikimedia.org/wiki/File:Parallax_barrier_vs_lenticular_screen.svg

[7]: Photo by Oculus. https://www.oculus.com/en-us/rift/