Displaying Stereoscopic Photographs

Putting the images back into your brain

 
 

There are many methods and techniques for displaying stereoscopic images but basically they all involve methods of feeding the left image into the left eye and the right image into the right eye. Each method has advantages and disadvantages in terms of cost, practicality, portability and convenience. We will look at just a few of them here, but an exploration of the web will reveal may more.


Anaglyphs

The viewer wears glasses with coloured lenses and the two images are coloured to match the lenses, they are displayed superimposed on each other. The coloured lenses feed only one image into each eye. The right eye’s lenses is always red but the left eye can be green, blue or cyan. This is for a monochrome image, you can get some colour information into the photograph if you take the red channel of the left image and overlay it with the green and blue channels of the right image. The right cyan lens allows more colour information to reach the brain and gives the best results The disadvantage here is that the viewer has to ware glasses and the coloured lenses don’t block all the light from the wrong image. This means some objects with strong colours don’t look so good due to there being more contrast between that object than the rest of the image. Despite this some very good results can be obtained with some images. Preparation of the images can be done in a photographic package like the commercial Photoshop or the free Gimp, alternatively specialist software can be used, like that available on this site.


Stereo Pairs

The images can be displayed or printed side by side and a pair of lenses or set of mirrors can be used to allow them to come into focus and fuse in the brain. The advantage of this is that you can have a full colour display, but the downside is that you have print them or use a clumsy mechanical device to view them off the screen. The majority of these devices use side by side images which are suited to a portrait aspect ratio however, the one shown on the left as an anaglyph is a View Magic viewer which uses an over / under arrangement best suited for a landscape aspect ratio.










Crossed polarised projectors

The two images are projected onto the same screen using two projectors each having a differently orientated polarising filter. The viewer has glasses with polarising filters matching the projectors. This gives excellent colour and allows many people to see the pictures at the same time. This is more popular with slide film than computers, although you can get a computer set up to do this, however, it is expensive.


Shutters

By rapidly flashing the left and right images alternatively on the screen, while at the same time blocking the left and right eye as appropriate you can feed each image into the correct eye. The simplest way to do this is by using liquid crystal shutter glasses and synchronising them to the display on your computer. The once plentiful supply of these glasses fuelled by the virtual reality craze of a few years back has dried up and the hardware to synchronies the switching to your computer is none standard. However, if you can get the kit together the results can be very good. A point to note is that there is usually a little bleed through of light from the wrong image as the glasses are not totally opaque when switched to block. Also the images tend to flicker a little due to the refresh rate being half what it is on the computer display. Modern LED and LCD displays tend to not to be able to respond fast enough for this type of display so a CRT is often the only option that will work correctly. A professional system like this can cost many times the price of your computer.


Head Movement

All the viewing methods suffer from one physiological phenomena, that is apparent when ever the viewer moves their head. The problem is that the brain thinks it is viewing a three dimensional object and when the head is moved from side to side the parallax doesn't alter. Therefore the only thing that the brain can do is to make it appear if the scene is rotating to compensate for the lack of perspective movement. It looks odd but it is the brain trying to make sense of what it is seeing.