Guide to 3D Photography

How To Free View Stereo (3D) Images

Viewing Stereo Pairs Without Special Equipment


When we look at something with our two eyes, we see in three dimensions (width, height and depth) because our brain interprets depth by comparing the two images from the left and right eyes. To simulate this photographically we need two photos of the same scene, taken from slightly different positions. This can be done using two cameras mounted together, or a multi-lens camera designed for stereo photography, but can also be done with just one camera - even the most basic type. Its simply a matter of taking one photo, moving the camera to one side, then taking another photo. Same scene, slightly different viewpoint.

This page describes a simple method of viewing 3D photos that any common person can see.
No special equipment, viewing devices or funny glasses are needed. All you need is your own two personal eyeballs.
The images below are displayed in 3D (three dimensions) using this method. The stereo pairs are to be "free-viewed" on the monitor - without using a 3D viewer - just the naked eye.

What you will be doing is staring intently at the pair of images and fusing them into a single 3D image. Each eye will be focused on only one of the images which the brain will perceive as a single 3D image. There are two types of free-viewing: "parallel" and "cross-eye".

When parallel free-viewing, images are presented with the left image on the left side and the right image on the right side. The left eye is looking at the left designated image, and the right eye is looking at the right designated image.

When cross-eye free-viewing, images are presented in the opposite order, with the left image on the right side and the right image on the left side. You are crossing your eyes and looking at the left designated image with the right eye and the right designated image with the left eye.

To see the 3d picture, what you want to do is to have each eye focused upon its corresponding left or right image. The brain will fuse the two images and you will see the image in 3D. When this occurs, you will actually see three images in a row. A flat image on the left side, a 3D image in the center and another flat image on the right side. Once you have the center image fused, you'll be able to move your eyes around to examine details of the 3D image and ignore the left and right peripheral flat images.

With both viewing styles, you want to relax your eyes and stare beyond the surface of the screen until you begin to see a double image. For the parallel method, you want to gaze straight ahead. For the cross-eyed method, you want to cross your eyes. For those new to free-viewing, using the cross-eyed method often produces the double image more quickly.

Cross-eyed 3D viewing will feel unnatural at first. This technique uses your eye muscles in ways you aren't yet used to. If you start to suffer eye strain or begin to get a headache, take a break and try again later. According to some eye doctors, it actually makes the muscles in your eye stronger, thus improving not hurting.

Have a rest if you feel any discomfort, as eyestrain can cause headaches and nauseas when experiencing this technique, especially the first times. It can take months to develop a comfortable and flexible control of your viewing mechanism though it worth it. A small percentage of people can't see the 3D images at all.

Tip: Move the mouse cursor out the image during 3D viewing.

"Parallel" method

The parallel method of viewing, like the cross-eye technique, is a rudimentary method of viewing in stereo without the use of technical aids. The parallel format has been used in the past almost exclusively, and it is still a standard for 3D image presentation in printed publications. It is more natural as you see more depth than with the cross-eye format.

This method also called "U view": Images are seen the same way as in a 3D viewer, using U or parallel vision. The eyes are relaxed to look into the distance until the images fuse, then refocused by the brain.

viewing the above image in three dimensions method will display four images while
the two images in the center are three dimensional yet different one from each other

To see the 3D picture "defocus" your eyes as you'd be looking at a very distant object, like seeing through. After some time you will begin to see three images. The images will fuse but are blurred because relaxed eyes focus into the distance. Keep the images fused until your brain works out how to adjust the focus. You will see three pictures. Now tilt your head until the three pictures are exactly aligned horizontally. The one in the center will be three-dimensional. Concentrate on the central picture and ignore the others - only the central picture is in 3D.

Note: If eyestrain or other discomfort is experienced, stop and take a break. Most people have trouble with the parallel viewing method because there is a tendency for our eyes to move outward in an unnatural way.

It is relatively easy to see small photo pairs, smaller than the distance between your eyes. For viewing larger photos in parallel method just move further away from the computer screen or try getting a stereo viewer, which can be purchased from several vendors. These devices have wedge prisms or lenses that can help to focus on the right and left images. Images on this site can be displayed easily via the parallel method without any additional accessories.

If you managed to see in 3D - congratulations! If you didn't, I encourage you to be patient and keep trying. Once mastered, it becomes easy and comfortable, and literally opens up another dimension in photography.

"Cross Eye" method

The easiest and most flexible method of viewing the two photos is the "cross-eye" method, where the photos are placed side by side with the "left" photo on the right, and "right" photo on the left. By slightly crossing the eyes, each eye looks at the photo meant for it. When the images match up and focus, the scene appears in life-like 3D, or a good approximation of it. This method can be hard to learn for the first time, but once mastered it is really quite easy. One advantage of this method, apart from requiring no equipment for viewing, is that the photos can be at any size.

The cross-eye is the preferred by most of people format in this computer age because it is easier to learn and allows seeing large photos. Big enlargements on a lounge room wall can be enjoyed in 3D from across the room.

This method also called "X view": Images are fused by going cross-eyed until the two pictures superimpose. Converging the eyes makes them focus close, and it is necessary to wait until the brain adjusts the focus for distant viewing again. You can also look around the 3D picture with the eyes locked into the correct format.

viewing the above image in three dimensions method will display four images while
the two images in the center are three dimensional yet different one from each other

To see the 3D picture ensure both images are level with each other. Its important to keep your eyes and the photos horizontal so that the images line up properly. If they don't, try tilting your head slightly each way and see if that helps. If you normally wear glasses, wear them to view 3D photos as correct focus is necessary. The distance from your eyes to the photos is not critical - whatever distance you normally sit from your computer screen should be fine. If you hold a finger in front of your face as close as you can while still being able to focus on it comfortably, then double this distance will be your minimum distance for viewing 3D photos.

Begin to converge your eyes, ie. go cross-eyed, but do it slowly. At first you should see four photos in front of you - two images for each eye - but as you converge your eyes the middle two should line up. This is what we're after: three images, with the middle one consisting of the left and right images merged together.

While keeping the two images merged, gradually bring them into focus. This is the tricky part! Normally when we look at something our eyes focus on whatever distance our lines of sight converge, but to view 3D with the cross-eye method we need to focus on photos that are twice as distant as the point our eyeballs are aimed at. This is not a natural skill, so it needs to be learned.

This is not an easy technique. Some people can master it in less than a few minutes, and others in more than one hour, but once you succeeded you will be able to see the 3D in less than a second later on. And it's really worth it!

There is a simple aid that will get rid of the distraction from the two side images, and maybe make it easier to see 3D stereo: cut a 1-1/2" square hole in the middle of a 5" x 7" index card (white or dark). For a quick test use scissors and 2 index cards and cut a 1-1/2" slot on both cards and staple the two cards together to get a square hole (it doesn't really have to be precise). To view the cross-eye stereo images hold the card slightly in front of your eyes as you look at the computer screen normally. Move it closer or further away from you to the spot where the right eye sees the left image only, and the left eye sees the right image only (close one eye at a time to check). Move your eyes to focus on the square hole on the card that you are holding. About midway between the card and the computer screen is the focus for the stereo image. At that point the two images automatically become one and in 3D. Relax your eyes, it is the same as looking at objects at different distances from you.

Taking the photos

The retina of our eye is a surface of photosensitive cells (receptors) distributed more or less like photoactive elements in a camera, so it gathers only a 2d-image. We see the depth only because we use two eyes and both eyes see objects from a different angle. These different points of view are transformed in our brain into a three-dimensional image. So, it is possible to see a 3d image on a flat monitor screen when two images, made form 2 different points (left and right camera) are presented.

There are several devices that make this task easy, but if you are new to this, it is likely that you don't have any of this equipment and must rely on free viewing. Fortunately, free viewing of 3d images is possible, but unfortunately it is not natural and requires some practice.

To simulate a 3D photograph we need two photos of the same scene, taken from slightly different positions. Its simply a matter of taking one photo, moving the camera to one side, then taking another photo.

Using any type of camera, take a photo in the normal way. Take extra care to keep the camera level, and remember what object is in the centre of the viewfinder. Move the camera to one side, position the same object in the centre of the viewfinder, and take the second photo.

How far do you move the camera between photos? For close objects, about the distance between your eyes. For more distant objects, a greater separation is needed to give sufficient depth to the photos. A rough rule of thumb is to move the camera at least one thirtieth (1/30) of the distance to the nearest significant object in the photo. If in doubt, experiment!

The best results are given by scenes containing both near and distant objects, and preferably something in between - this gives a greater sense of depth. Things receding into the distance - such as roads, railway tracks, fences - can work well. Far-off scenery without a prominent foreground can look flat, even with wide camera separation.

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