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3D viewing methods

After such a long time waiting for it, according to my web page statistics, I finally get into realizing this part about all methods allowing the observation of the third dimension. As it is, nearly every time, a question of tool, it seems convenient to me to sort by that criterion.

Standard eyes | Trained eyes | Viewer | Passive glasses

Use of a standard pair of eyes.

Standard pair of eyes
The first tool available is the absence of tool!
This is to say the use of our stereoscopic viewing base equipment: Our two eyes and our brain to traduce the viewing of two images in volume. I stop for a kind of small philosophy asset. Mother Nature gave to all animals at least a pair of eyes with two king of disposition:
- Side by side with parallel axis. This is the way human eyes are set and more generally predators. This is to say living beings able to locate precisely in space a moving object and able to catch it. In the Nature, that is evidently eating that same object, witch make this character a must for predators. Human beings found a lot more applications to that ability such as ball games...
-The more unlucky, but also more tasty, animals, such as herbivores have generally two eyes offering a vision more panoramic than stereoscopic. For them, it’s better to be vigilant than to see the third dimension.

Usual space viewing

Statue
Maybe it seems strange, but the more simple way to reproduce an object or a person in 3 dimensions is to realise a copy in form of sculpture, moulding, or scale model. It as old as the world, but still works well! Even the Nature try it copying its own creation as fossils. That method is not very exiting but provides a genuine 3D effect. It is possible to paint the artwork of whatever manner to reproduce the model colours. Several people, blind included can enjoy the volume from any point of view at the same time.

Holograms

Hologram
This is a very technique and quite modern to do the same thing as sculpture. The main difference is that, in spite of having a real, you get a virtual volume to be seen inside a paper sheet or through a transparent film. The 3D effect is incredible, you can change the point of view. Nevertheless, colour reproduction is not possible.

Lenticular lens

Lenticular lens
The printing of alternate slices of both views is seen through a network of thin hemi-cylindrical lenses. Each eyes just sees what it should see. The 3D effect is quite excellent (if the shooting is good, of course !), reproduction of colours is as good as any paper print. The effect is to be seen from a determined point and only by one person at a time. A better version use more than two images, not being stereoscopic, and provide better viewing comfort. Some computer screens, parallax-barrier based and seem quite interesting (and also kind of expensive!).

Standard eyes | Trained eyes | Viewer | Passive glasses

Use of a trained pair of eyes.

Trained pair of eyes
Here begins the area of stereoscopic images, resulting from two shootings (see “Anaglyph, what a hell is that?” et “Stereoscopic shooting”). Both images of a stereo-pair can be viewed as presented. Following are the two “free vision” methods requiring no tool.

Parallel viewing

Parallel viewing
The two images stand side-by-side. The image corresponding to the left eye is on the left side, and the right image at the right side. Although it seems natural, it is not possible to use a pair of big images because our eyes are not able to diverge such a way.

Crossed viewing

Crossed viewing
In that case, images the right image stands at the left whereas the left image stands at the right side. It is not easy to “cross the view” but that methods allows the observation of pairs of big images.

L-R-L or R-L-R

L-R-L R-L-R
One of the two images is repeated once though it is possible to view both parallel and crossed ways selecting 2 out of the 3 images.

Between the parallel and the crossed viewing, there are perpetual fights among pros and cons of either one or other method. Some just considers the “crossed” one and others only the parallel. Others, like me, are not able to cross the view, so unable to cross-view. Some others, too familiar with cross-viewing can’t anymore see parallel pairs. In order to all those people to agree, there is a lot of devices to facilitate the viewing of both kind of pairs. Those apparatus, called viewer, will be seen in the next chapter. But before switching to those helpful apparatuses, one more method is remaining for top-trained eyes.

Stereograms et autostereograms

SIRDS
They consists of 2 dimensions images of drawings witch can be seen as 3D when looked a certain way. Maybe you remember some years ago, that world-famous “magic eye”. These are Single Image Random Dot Stereogram (SIRDS) and you can see a nice example following that link or a nice collection in the Webpage of Dominique Notteghem.
As with stereo pairs, there are crossed-viewing and parallel-viewing versions.
This method does not allow to record the three dimensions but to build it and stuck it to a pattern. It is not possible to reproduce colour but the 3D effect can be very intense.

Standard eyes | Trained eyes | Viewer | Passive glasses

Use of a viewer.

Viewer
Viewers are optic devices guiding each of both images of a stereo pair through the corresponding eyes. Three kind of optic elements (mirrors, lenses and prisms) could be used or combined.

Mirror (Wheastone stereoscope)

Wheastone Stereoscope
?  
The first ever stereoscope was patented by Charles Wheatstone in 1838, nearly at the same time a fantastic technique and form of expression was created ; nothing else than photography itself.
Bad thing: In the original version, the two images are left-right mirrored. A more modern design adding a second pair of mirrors put the image the correct way.

Lenses (Brewster Stereoscope)

Brewster type Stereoscope
?  
In 1849, David Brewster (also inventor of the Kaleidoscope) invented the principle of the two lens stereoscope.
Defect: Apparatuses generally quite bulky witch can be used just by one person at a time.
Advantages: Good vision of 3D and ease of manufacturing. It provided a lot of mythical stereoscopes such as Vérascope, Bruguière and Lestrade Stereoscope, the ViewMaster and more recently 3D postcards (simple stereo-pair with two lenses in a folding cardboard box).

Prisms (Holmes Stereoscope)

Holmes Stereoscope
?  
Starting from Brewster’s work, Oliver Wendell Holmes set-up the stereoscope using prismatic lenses. It gave a device easy to carry, that was presented in a publication in 1859. He decided not to patent its creation, so he is a precursor of the authors of free softwares used by the majority of stereoscopists to mount images <;o).

Two small screens visor (Head Mounted Displays)

Head Mounted Display
?  
This is the modern version of the viewers described before. In that case, it carry two small screens connected to a computer in front of each eyes. That system is very similar to the Head Mounted Displays included in the helmets of the fighter pilots.
Advantage: It is possible to see moving pictures and also movies with that system.
Defect: the spectator’s head is set into a kind of box quite impressive.

This type of viewing the third dimension using viewers has the great defect to be individual. Of course, it could be considered that the kind of initiation, such as peace pipe, is an advantage: The viewer goes from hand to hand sharing slowly the three dimensions. But, when the group is more than half-dozen persons, the session is majority of waiting times. The remedy is to use projection-based methods.

Standard eyes | Trained eyes | Viewer | Passive glasses

Use of a pair of passive glasses.

Passive glasses
The methods allowing the three dimensions to be seen by a big number of people are quite similar. There are always a pair of projectors , one for each of the two images, more a pair of glasses performing the separation and viewing of each image by its corresponding eye.

Anaglyphs and company

Anaglyph and amber-blue glasses
The principle and the making are simple. It consists in making the separation of both images of the stereo-pair using two coloured filters. This process was discovered by Wilhelm Rollman in 1853 using red and blue line on a black background. In 1858, Joseph D’Almeida realised the first 3d projection with a magic-lantern and viewing with red-green glasses. Finally, Louis Ducas du Hauron in 1891, invented and patented the successive printing of the two images of a stereo-pair on the same paper. the first one in red and the second one in green (or bleu).
Defect: The use of blue or green opposed to the red forbids the correct viewing of colours, whereas choosing the cyan instead, leads to a quite correct reproduction of colours if neither of the two filters colours are present. There is a kind of “norm” consisting in putting the red filter in front of the left eye and the cyan filter in front of the right eye. Some smart people, are still patenting optimised process by changing the colours of the filters used. There is no special advantage and the defects are also the same. It can be noticed that the amber-blue combination sold in quantity as “Color Code” works quite well for tomatoes with blue sky as a background. Nevertheless, it causes great visual discomfort due for the great contrast between the two filters.
Anaglyphs are now developing its number of fans because it is easy to set and view on a computer screen or with video-projector. To shows that you may have a look at the very active Yahoo group “Anaglyphs” (11676 messages in 2005 with a great proportion of anaglyphs in the posts). If you want you can have a look at the group’s archives and see the artworks of the world greatest anaglyphs creators. Of course, you can sign-in for this Yahoo group and post your anaglyphs on it in order to take profit of advices of members to progress with the help of the very best specialists.

Polarised

Polarised glasses
The separation of two projected images by means of a pure optic process should seams magical. There is another solution using polarised filters. Each of the two projectors is equipped with polarised filters with the polarisation plans set at 90° difference between both. Glasses are composed by a pair of filters with the polarisation set the same way as the corresponding projector. That’s it! Well, nearly, because you need a projection surface conserving the polarisation of the light. This is the first problem, a silver screen, so expensive, if compulsory. There are two more disadvantages. Due to a certain lose of light by the polarisers, it is necessary to use potent projectors. The setting is more complex than the setting of conventional slides.
Advantages: The reproduction of colours is very realistic. The polarised glasses are, as anaglyph glasses, quite easy to buy and cheap. Thus, that method results, the favourite of stereoscopists for group presentation.

Use of an active separator.

Active separator
In spite of projecting the two images at the same time and subsequent trying to separate, it is possible to project only one image at a time. In that case, the ghosts due to the partial mixing of the two images are completely removed. The 2 images are projected alternatively, and it is called field-sequential system.

Shutter glasses

Shutter glasses
Although, IMAX 3D movie theatres are now using it for quite a long time, this system is one of the more modern. A device synchronised with the movie shows alternatively one image a t a time to each eye. The frequency of alternation is, in the case of IMAX, of 96 frames per second. So no flashing is seen. In the case of home videos the best rate is 60Hz (in the case of NTSC), witch is equivalent to see the scene at the rate of 30 half images per second so a resulting sensation of 15Hz, frequency slow enough to guaranty headache. Let’s not speak of the PAL and SECAM offering to the eyes a show at 12,5 images per second.
In order to permit to each eye to only see its corresponding image, the device (active glasses) hide alternatively one eye synchronically with the screen.
Advantages: Easy to set-up, even on a big screen,, if you have the hiding device.
Disadvantages: Price of the device included actives, so expensive, glasses for each spectator.

Passive glasses with Byatt modulator (Liquid Crystal Color Shutter)

Byatt modulator
In spite of separating the two images with active glasses, a very amazing device can be used: Byatt modulator. It consists of a plate containing liquid crystals with the ability of fast polarisation change upon the action of an electric field. A pair of normal polarised glasses is then required to view the 3D. In 1993, I had the great opportunity to use the CAChe (Computer Assisted CHEmistry) chemical modelling system. The system was composed of a configuration calculator (program running on a IBM RISC 6000 station, no relevant in our case) and a computer, it was a highly powerful Macintosh (probably a 33MHz Quadra 800!) and especially a special graphic board with a “3D Tektornix” screen (as Tektronix was tear apart, the software is now sold by Fujitsu-Siemens and the screen must be the MacNaughton Inc. NuVision according to my Google search).
At that time, I was not a stereo-photo addict but I imagine that same screen in the cellars of my laboratory of that period ; poor fellow how it must be boring! Maybe it is just the memory that makes that system one of the best I ever test to view 3D? Of course I was looking at “MY” molecule. That image is reconstructed with RasMac 2.7.2.1 from the 1993 “.pbd” file resulting of the optimisation with the Tektronix system. the only thing remaining except what I remember.
Advantage to the previous system: Use passive, thus cheap glasses.

   

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