How to View Parallel Stereo Imagery

Truth be told, I create anaglyphs because so many people find viewing pictures in parallel, freeview format impossible to deal with. Perhaps so. But if you have fairly equal vision in both eyes, can read this (which is close to your eyes), and look up outside and see the Moon (which is 250,000 miles away), or the Sun (which is 93 million miles away, and as an aside, there you have an answer to the age-old question, "How far can you see on a clear day?"), you should also be able to freeview parallel pictures.

Why? because the principles are the same. However, you need to be able to simultaneously bring things close to you into focus while aligning your eyes to converge at (practically) infinity. That is, your eyes need to drift apart (diverge) until they are viewing along (nearly) parallel lines. Here's what's going on...

In real life, your two eyes are seeing slightly different information when looking at a nearby object. Take a look at these two pictures of a box and a cylinder on a table. They are what your two eyes might see in real life. The picture on the left shows the centerline of the cylinder lining up with the far, right edge of the box, and is how your left eye would see it. The picture on the right shows what your right eye sees: the cylinder's centerline appears just right of the same edge of the box, and the table is less foreshortened - you see the side a bit more face-on. Your eyes see slightly different information. Here's a bird's-eye view of (a stylized) you, the table, and the objects. The dark blue line shows your left eye's line of sight, and the cyan shows your right's. Your left eye sees the side of the table at a very shallow angle, and your right eye sees it a bit more face-on. In real life, you see this scene in 3D. The view has depth. The third dimension is synthesized by your brain from two images - one from each eye. To create a stereo pair of any sort, you have to start out with two images. Hence, I suppose, the term stereo pair. One image is composed for and destined to be viewed by the left eye, and the other for and by the right. In the real world, I take a picture of a subject as seen by the left eye, then physically move the camera an appropriate distance to the right and take a second shot of the same subject, maintaining all sorts of orientations and alignments (if I do it correctly). To view the pair, I place both frames side by side into one image file. Then I freeview that image. Freeviewing can be difficult because you have to be able to allow your eyes to diverge as if looking at a distant object, yet maintain sharpness at the distance of the picture pair you're studying. I imagine looking at distant mountains, keeping a check on when to stop allowing the frames to drift around. When the frames are merged into one, I try to focus, which then comes fairly easily. This is sort of what it looks like:
At first, it appears the two image split into four, because as your eyes drift apart, each eye sees the two. You'll see the two inner images merge into one, with two leftovers at the sides. Ignore the two images on the sides, and concentrate on the middle image. Your eyes will focus almost automatically, and the middle image will appear 3D!
Things that make images "better" for you
One thing that is very difficult (if not impossible) for virtually everyone, is moving your eyes to spread wider than parallel: to diverge. That means if a pair is wider apart than your eyes, you're not likely going to be able to get your eyes to spread apart to reach their proper positions. There are several alternatives: If the image is on the computer, you can increase your resolution, effectiviely "shrinking" the image. Actually, the pixel density increases and the image takes up less room. Whatever, the image gets smaller, and the pairs closer together. This is a good way to do it, because you lose no information on the picture - it just gets smaller. If your picture-viewing software allows, you could zoom out. However, you'd lose image information when doing that, and it's also unlikely that information would be missing in corresponding areas from both frames. So the effect would look worse in a stereo pair than on a standard image. Use a smaller monitor. (not likely, eh? I wouldn't, either) Use image-editing software to resize the images to your own personal best. If you can get your eyes to go divergent at all, then backing away from the screen/image would work. Cross pairs are an alternative to parallel pairs. In this format, the left and right panes are swapped, and you cross your eyes. Many people who can't parallel view, can cross view. My personal preference is for parallel though, and that's how I create and post my images. The anaglyphs are "extras". You can click here to view samples of different sizes of parallel pairs. Try viewing the smallest (easiest?) one first, and work your way down to the largest one - the size I post here normally.