Stereo Photography Basics

In order to provide the required depth in a stereo image, one must first begin with a left and right pair. Each image must present a slightly different perspective of the subject, just as our eyes do for us to perceive depth. This can be achieved by many means, but the ultimate goal is to try to capture and present what the human eyes see. There are several rules of thumb in stereo photography, but probably the most important one concerns how much to move the camera between the left image and the right image; this is often referred to as the stereo "base". (It should be noted here that, for most practical purposes, the camera should move along a straight path, with lenses always facing straight ahead, throughout the left-right shift. "Toeing in" does not usually provide acceptable results without employing a very complicated mathematical process.)

As a starting point, you will typically want a base somewhere close to the distance between the human eyes, which is around 2½" (65mm). But there are many cases where you'll want to use a shorter or longer base, depending on your distance to the subject. Because of this, the rule of thumb to consider is the "1 in 30" rule. Put simply, the stereo base should measure approximately 1/30 the distance to the nearest subject. Of course, this is not always a practical way to go, especially when working with a camera with fixed lenses, such as a dedicated stereo camera. And as with all rules in photography, there are cases where you'll want to break the 1 in 30 rule for the sake of artistic creativity, such as going wider than normal to exaggerate the 3-D effect.

Once the stereo pair is created, a considerable amount of thought should be put into how the resulting image will be presented. One of the key elements that can make or break a good stereo image is how it is registered within the "window". In the world of stereo photography, you'll often hear the term "through the window" or "window violation". These are not necessarily one in the same, although a window violation will most likely be coming through the window. Imagine you are actually looking through a window in your house, only

there is no glass in it. You look through the window to see what is outside. If someone reaches through the window toward you, their arm now protrudes "through the window". Note the illustration to the right. The man's arm extends beyond the "frame", toward the viewer, but the rest of his body remains behind it. This type of protrusion can appear very natural, and can provide for a very captivating image, often referred to as the "comin' at ya" approach. But if only a portion of the man's arm/hand were visible in the photo and you used the same registration, you'd have a portion of it coming through, but the rest would be missing. You'd be better off adjusting the registration so that all of the man stays behind the window and then his hand logically falls outside the field of view. Likewise, if you were to allow a tree from outside to partially protrude into the window, say, along the bottom of the frame, the result would be a very confusing anomaly; half of a tree would be floating in space in your house! How you choose to register your stereo pair will determine what, if any, elements of the image protrude through the window. It is only through experience and practice that you will gain a good working knowledge of how to use the stereo window effectively.

In the anaglyph samples above, note how the clown's foot protrudes through the frame in the right version, but stays behind it in the left version. This is completely controlled by the registration of the left and right images.

Once the basics are understood, you'll want to start creating stereo images! There are many ways to go about editing your images; your choice may be dependent on your own preference in software, or your budget. Full-blown image editors such as Adobe Photoshop and Paint Shop Pro work great for creating stereo images. There are also a good number of dedicated programs available for stereo imaging, both commercial and freeware. Here are a few:

Commercial and Shareware

ProMagic

Pokescope

3D Stereo Image Factory

Freeware

Stereoscope Java Applet