3D photography
You don’t need to buy a special expensive camera to take three-dimensional photographs, as Mike Bedford reveals.
You don’t need to buy a special expensive camera to take three-dimensional photography as Mike Bedford reveals how to do anaglyph in Gimp.
We might live in a three-dimensional world but, by and large, our cameras are firmly rooted in two dimensions. Occasionally, a manufacturer will release a 3D model, which can be identified by its two or more lenses, but these are by no means cheap and, as a result, they rarely catch on.
The fact is, though, that you can enter into the world of 3D photography with nothing more specialised or expensive than an ordinary camera, as we’re about to see. First, we’ll look at what we mean by 3D photography and describe, in general terms, how it works. Next we’ll provide practical instructions on how to take a photo that can be viewed in 3D. And finally we’ll delve into the various ways of processing your photos so they can be viewed in all their three dimensional glory.
We’ll look at off-the-shelf software and we’ll also see how to manipulate your images with ordinary photoediting software. Then, for those who fancy churning out some code, having learned the principles you’ll be in a good position to write your own software.
Into the third dimension!
As a prelude to delving into the practicalities, it’s important to explain what we mean by 3D photography. The human visual system uses several ways of perceiving depth and many of these are present in runof-the-mill photography. So, for example, ordinary photos display perspective, which is an important way of differentiating near objects from more distant ones. Similarly, all photos capture the way that nearby objects partially obscure distant ones and that colour becomes less saturated at distance.
However, one visual clue is missing: stereoscopy. This relies on the fact that we have two eyes and we can, therefore, view the world from two slightly different viewpoints. Although it happens subconsciously, this enables our brain to estimate the distance to objects in the scene through triangulation and the result is a sense of depth. Normally, when we refer to 3D photography we’re talking of a method of capturing and viewing a scene that makes it possible to experience stereoscopy.
In principle, this is simple enough. In capturing the scene it’s necessary to take a pair of photos, which constitutes a stereo pair, and to view them a method is required that cause the left eye to see only the left-hand image and the right eye to see only the right-hand image. There are several ways of taking a stereo pair and even more ways of viewing them, as we’re about to see.
It’s fairly obvious how a dedicated 3D camera works. In the simplest of cases it has two lenses, separated by the same sort of distance as our eyes, so it’s able to capture that all-important stereo pair. It’s also possible to buy adapters for ordinary cameras. These are optical devices that use mirrors or prisms that enable the image from two slightly different viewpoints to be routed through the camera’s single lens. Both methods are expensive so we’ll look at a few alternatives, two of which will cost you nothing, and the other just a few pounds at a DIY store.
All these methods make it possible for two images to be captured from two different viewpoints, using a single camera. Often it’s suggested that the two viewpoints should separated horizontally by 70cm, the distance between our eyes, but feel free to experiment. Some 3D photographers, for example, suggest a 30th or a 50th of the distance between the camera and the subject for distant objects, and a quarter of the distance for close-ups. The further the separation, the more exaggerated the effect.
The first method works only with optical viewfinder cameras – as opposed to those with just an LCD viewfinder – and doesn’t cost a penny. Compose the photo while looking through the viewfinder with your left
eye and press the shutter release. Move the camera and look through the viewfinder with your right eye and take another photo. The result might not be perfect, and it probably means that you’ll have to correct any changes in the vertical distance between shots, but it’s worth a try because it’s free and easy.
A variant on this technique, which will work if your camera only has an LCD viewfinder, is to brace your camera in front of you and compose and take a shot with your weight on your left leg. Then transfer your weight to your right leg and take another. You’ll probably have to experiment to get a repeatable distance between the two shots. The proviso for both these methods, and the one we’re about to see next, is that the scene mustn’t contain moving objects, and if you have a human subject ensure they remain perfectly still!
Two legs good, three legs better
A better method is to use a tripod and a device that enables you to move your camera a set distance between shots while also making sure there are no unintentional movements. Such devices are available commercially, and are called slide rails, but it’s easy to make something that’s almost as good – let’s call it a slide box. It comprises a flat horizontal base along which you slide your camera, a back to ensure that the camera stays at the same distance from the subject and always points forward, and sides to provide end stops at the necessary separation to ensure your chosen distance between the two shots.
The exact dimensions vary with your camera and whether or not you need to be able to see the LCD display, but the photo ( belowleft) gives you a good impression of what it should look like. This can easily be constructed using chipboard with the joints glued and pinned. You also need to attach a threaded screw into the bottom of the base so that the screw on your tripod can attach to the slide box. You might also want to line the inside of the back with fabric, to prevent the LCD panel from being scratched when you slide the camera. Using it is simple enough. Level the slide box on your tripod and place you camera in it so it sits against the back and left. Frame your shot using the tripod’s adjustments and press the shutter release. Slide your camera along the back until it stops at the right edge and take another photo.
A bit of practical advice might help. First, try to take the two shots with as little times as possible between them to avoid the problems of any slowly moving objects or changes to the lighting. Second, it’ll be much easier if you always take the two shots in the same order so you can identify the left and right images afterwards – our instructions assume left then right. And finally, you’ll find that stereoscopy is a subtle effect at long distances so choose scenes that have objects at a range of distances, some quite close to the camera.
Next up we’re going to look at methods for processing and viewing stereo pairs so, before you get too embroiled in that, it would be a good idea to try your hand at stereo photography using one or more of the methods discussed. Then, with your stereo pairs at the ready, you can learn in a practical way about the second stage of the 3D photography process.
The simplest method of viewing a stereo pair is to display the two images side-by-side, either on a screen or printed page. So long as they are reproduced quite small – about 65mm wide with very little gap between them – these can be viewed without any special equipment. This free viewing technique takes a bit of practice and requires the same sort of skill that’s required to see Magic Eye images. It’s not easy to put it into words – and you’ll undoubtedly have to experiments – but here’s the gist of the visual gymnastics that’s required.
View the pair of images from a comfortable viewing distance of about 300mm. Now try to defocus your eyes so that you end up seeing three images: the left image, the left and right images overlapping, and the right image. Finally, and this is the tricky part, concentrate on the centre combined image and try to bring it into focus while still maintaining that combined image. If you succeed, you’ll see it in 3D.
Side-by-side images can be viewed more easily using an optical device called a stereoscope and, depending on the model, these can also be used for larger images. Low-cost stereoscopes are available from Loreo ( www.loreo.com). The company is based in Hong Kong, so delivery might not be as quick or cheap as you might hope, but its products are available from a few