Viewing in 3D

When you view a three dimensional object in the real world your left and right eyes see slightly different images and your brain interprets the difference to give a sense of the real shape of the object.

Therefore to allow your eyes and brain to see a Blender model in real 3D your eyes must be presented with two different images seen from slightly different positions (your eyes are between 6 and 7 cm apart).

Once these two images have been obtained there are various ways of ensuring that each eye sees the correct image:

Stereo viewer

When such a device is held up to your face, lenses, mirrors and/or prisms ensure that each eye only sees the image that is intended for it.

The cross-eyed method

Like the above method, this uses pairs of full-colour images that are placed side-by-side. However in this case the image for the left eye is on the right and the image for the right eye is on the left. This means that the person viewing the images must cross his eyes to get the desired 3D effect. This is a technique that must be learnt and which some people find a bit difficult. Here is an image-pair designed for the cross-eyed technique:

For more information, including advice on how to succeed the eye-crossing technique, see

spdbv.vital-it.ch/TheMolecularLevel/0Help/StereoView.html

A similar method can also work with images that are not reversed so that in fact you do not need to cross your eyes. Instead, your eyes need to diverge which never happens in everyday life and which therefore may be even more difficult to learn than the cross-eye technique. Viewing with diverging eyes is called ... divergent viewing (a opposed to the cross-eye technique which is also called convergent viewing). Actually the divergent viewing technique will work just fine even if the separation of the image centres is about 5cm in which case your eyes will not actually have to diverge. Here is an example of a divergent image. The trick for seeing the divergent image is to let your eyes relax and look well beyond the image. Once the images seen by each eye overlap so the brain can begin to 'lock on' to them then you can try to focus your eyes for the final 3d effect. If you are short-sighted then it's probably helpful to remove your glasses or contacts when looking at divergent images such as these.

You may find it more comfortable to look at the middle two images of the sequence below. The outer images are identical to the inner images. The presence of additional images either side makes you less aware of the disturbing 'one-eye' images that you otherwise get on either side. Don't forget these are 'divergent'images - you should be trying to 'look beyond' these images rather than trying to cross your eyes.

Your eye has colour-sensitive cells capable of detecting red, green and blue (the primary colours). We see other colours when these cells are stimulated together - for example we see yellow when the green-sensitive and red-sensitive cells are stimulated together. The image to be seen by the left eye has its blue and green components removed so that only red is left. It is then viewed through a red filter which transmits only this colour and blocks the cyan (blue-green) image destined for the right eye. The image to be seen by the right eye has its red component removed so that only blue and green are left. It is then viewed through a cyan (blue-green) filter which transmits only blue and green and blocks the red image destined for the other eye. Here is an example of an image designed to be viewed through red-cyan glasses.

Such an image is often called a 'stereoscopic image' or an 'anaglyph image'. To see more, do a Google image search for 'anaglyph'.

3D coloured glasses can be ordered on the internet for about 1 Euro per pair and are sometimes included in magazines.

Polarised lenses

This method is similar to the coloured filter method described above but in this case the viewer wears glasses containing polarising filters. The left eye looks through a vertically-polarised filter that lets through only vertically polarised light and the right eye looks through a horizontally-polarised filter that lets through only horizontally polarised light. The advantage of this method is that each eye sees a full-colour image. The disadvantages include the fact the technique only works when projected only a metallised screen (it won't work with an image on paper or on a normal TV or computer screen) and it also require that the viewer does not tip his head at all.

Electronically-controlled LCD shutters

This is the most sophisticated method and is the method that has been used by several recent movies such as Avatar, the most successful movie of all time (to 2010). The images to be seen by the left eye and the right eye are shown alternately, one after the other, in quick succession, and a synchronisation signal is beamed from the screen to the special glasses instructing the glasses to block the left lens when the image for the right eye is being shown and vice versa. This requires specially prepared video, fat screens, a synchronisation technology and special glasses. It is now possible to buy TVs and computers using this technology, but will it ever become really popular given that it require the wearing of special glasses?

Magic Eye

I'm sure you've already seen 'magic eye' pictures like this one:

I certainly hope so, for I don't have time to explain to you how to see the hidden image, or how these images work. There are plenty of websites that try to just that, however, such as www.magiceye.com/faq_example.htm

A clue as to how magic eye works is the following image, which is like a hybrid between 'divergent viewing' and traditional magic eye in which the image is seen by neither eye - it is only detectable in the difference between what the two eyes see:

I find the above image much more comfortable to look at than the convergent or divergent image pairs described earlier, don't you? By the way, if you are short-sighted then remove your glasses or contact lenses for easier viewing of the convergent, divergent and magic eye images. Also note that in many cases it may be easier to successfully view these images printed on paper rather than displayed on a computer screen. You can easily find more magic eye images by doing a Google image search if you're interested.

Here's one more magic eye image - it's rather unusual in that it's made with text. Can you read the hidden message? I'll give you a clue: it's seven words long...

Youtube 3D

It is now possible to publish videos to Youtube in such a way that the viewer can choose between several of the above methods including cross-eye, red-cyan, red-green etc. The two source videos must be combined into a single video with the left and right hand signals side by side For more details visit the Youtube site. See also

http://googlesystem.blogspot.com/2009/07/youtube-3d.html

http://www.pocket-lint.com/news/27278/10-youtube-3d-videos-watch