My son Ronan and I were looking through an old ViewMaster (it was my dad’s when he was a kid) yesterday, and we decided to shoot our own stereographic image.
The idea behind shooting 3D images is to take two identical photographs offset horizontally by approximately 2.5″. This is the average interaxial distance between human eyeballs. If this website were visited primarily by hammerhead sharks I’d have to widen that separation distance.
Fancy stereoscopic camera rigs have two lenses on a single camera body, or two bodies and set of mirrors and lenses to achieve that distance. Or, you can simply take a photo, slide your camera sideways and take another. This works for still subjects only.
I build this simple rig out of chemistry lab equipment. (Yes, it’s the same bar stand and clamp set I used to build my Florence Siphon vacuum coffee brewer apparatus.) I pulled my focus and other settings, took a photo, slid it all about 2.5″ to the left and shot a second photo.
Next comes the image processing. What we need to do is paste the left eye image on top of the right one, then line the photos up so that they line up exactly at the point of zero stereo effect. I chose the button protruding from the far side of my typewriter. This is the plane on which the viewer sees the image, and there should be no difference between the left and right images.
Next, I cropped the image to remove the offset edge difference. If you don’t do this one image seems to float in front of the other at best, and at worst, the person viewing will get a mild headache and bleed out of their eyes.
To fool the brain we need to show only the right image to the right eye and the left to the left. There are many ways to do this. The ViewMaster displays two images through two lenses, one for each eye. The method I chose here is called an anaglyphic image. To make this I used Photoshop levels command to remove all the blue and green from the left image and all the red from the right image.
I used the screen compositing mode on the left image, and the result is an image where the common pixels are seen by both eyes, while the differences are only seen in the appropriate eye when you wear red/cyan 3D glasses. This site has a good step-by-step of the Photoshop side of things.