Stereo Imaging

To understand stereo imaging, let's think about normal vision.  Most people experience stereo vision without being aware of it.  Close one eye and look across the room. Now switch eyes and the scene changes slightly. With both eyes open, your brain is converting the differences in the two scenes into depth information.  The result is that you see in 3D.

Stereo Photography

The same principle is used to produce stereo photographs. Two cameras, separated by some distance, are used to take images of the same scene.   Just as with your eyes, the two views produce images that differ slightly due to the different perspectives from the two cameras.  Using a stereo viewing device (or learn free vision, described below) the left image is presented to your left eye and the right image presented to your right eye.  Just as with normal vision, your brain does the rest and you see 3D.

Cameras have their limitations when compared to the human eye, but they also have advantages.  The difference in perspective visible to your eyes is limited by the inter-ocular distance.  With cameras, we can increase the distance between the "eyes".  This "hyper-stereo" view increases the differences between the views and enhances the 3D effect.  USA Aloft uses two cameras, separated by about 15 feet under the wings of a Cessna 172 to make its aerial stereo shots.  Read more about the technology supporting USA Aloft's stereo photography system.

If you don't have two cameras, you can get the same effect by taking a picture, moving to the side and then taking the second picture.  As long as nothing in the scene has moved appreciably in the time between the two pictures, you can use the two images to make a stereo pair. 

Try this with your own camera; it works!  Aim your camera at some subject.  Take a picture.  Take a step to the side and take another picture.  Make sure you aim at the same point and keep the camera level for both shots.  Put the shots side by side as shown below and you have your first stereo pair.  Of course, you can get much more technical; choosing separation to match the subjects, using depth of field and aligning the images are a few of the issues important to good stereo photography.

Stereo Viewing

Once you have a stereo pair you are faced with choosing a device to view it.  Here are a few of the ways it has been done.

Our Software

So what are we going to use?  The answer is that we haven't decided yet.  Here is what we know.  We do have a stereo viewer that allows the user to pan and zoom images.  This display will be used to present image pairs in free vision and cross-eyed formats.  We may offer some low cost stereopticon either with the software or as an option to be used with this viewer.  We may also offer a range of these devices from our web site.  We are investigating the use of anaglyphs as an additional display method.  Our viewer will be configurable for use with some of the other hardware solutions, including the polarized solutions, but we do not currently plan to offer that "out of the box."  We attended the National Stereo Association convention in Portland, OR in July looking at the latest hardware.  We saw a laptop from one vendor that offers direct, stereo viewing with no special glasses.  We do not think the technology is mature yet, but we will want our solution to be compatible. We will shortly be making final decisions about this aspect of our software.  Stay tuned.

Free Vision

It is possible to view stereo images without a viewer. Focus on an object in the far distance to get your eyes lined up on parallel paths. Bring the two pictures up into your field of vision and try not to focus on either picture, but rather just let your eyes kind of stare. What should happen is that the left eye looks at the left picture and the right eye at the right. Staring like this, the picture will pop into 3D for many people.


Other Stereo Information

David Saxe's first experience with stereo imaging occurred while creating representations of factor analysis solutions using graphics in the Speakeasy language in the early 1970's.  To read the NASA description that he used to learn about free vision, read the caption to Figure 8 in "On the Moon with Apollo 17, A Guidebook to Taurus-Littrow" by Gene Simmons. (NASA, Dec. 1972, USGPO Stock Number 3300-00470.) The description, attributed to Earl E. Krause, is somewhat more detailed than that given above.

For more information about stereo photography, visit the National Stereo Association.  USA Aloft attended their annual convention held July 7 - 12, 2004 in Portland Oregon.