3-D Projection

Technically, stereoscopic film provides for an enormous challenge.
If just for the multiplicity of available systems for recording, playback and viewing. What's possible, what's not, and how to make just that happen anyway.
Think theatre projection, television and computer monitor display. It's all options, and all technical mayhem.
But when it works, you've got your ooh's and aah's.

These pages discuss stereoscopics from a filmmakers perspective. Summing up dates and cool 3D movies is not going to help a stereoscopic filmer get his 3D stuff done. And there's too little help from the big 3D companies anyway.
These include: Iwerks Entertainment, Kleiser-Walczak, Rhythm & Hues Studios, Mainframe Entertainment, Sony Pictures Classics - Large Format, and Nwave Pictures.
The information of these pages is gained through professional and personal research and experience with 3D filming and projection.
One emotion rules any research in 3D: total confusion. Because it is such an intense experience that people love to share (through stories and internetsites), a whole lot of enthousiastic screaming and shouting takes place, blurring and burying useable information on the subject.
Also, commercial sites trying to sell their 3D glasses and 3D projection systems provide a lot of discussable facts about stereoscopics, or pull up a smoke screen to dizzy the site's visitor.
So here's the step by step story, hopefully as clear and objective as possible.

The systems discussed are those commonly in use at Cinema theatres. Systems like hollow screens, passive 3D screens, Cinerama, Viewmaster-type, lenticular, cross-eyed viewing, Magic Eye and Pepper's Ghost (A.K.A. Holavision) techniques are not realistic options with accesible (home) Cinema audience display, and will not be discussed here.

Let's start with the most important question of all: what do you want.

Since the technical possibilities do dictate how you have to shoot, what it's going to look like and how you are going to present, one has to start asking these questions first:

- What are the Projectional possibilities and where is your audience going to see the film.
- Is there need for Color, or can limitations of a system become a stylistic plus.
- How Close do the objects in the film have to get to your face when they stick out of the screen.
- What's the Budget and what do I want to spend the money on.

Projection

First thing you need to know is how you are going to present the film. The are a couple of systems, and a couple of ways to use them.
Projecting options include StereoVision/VariVision Polarized film, Polarized beam of TV/RGB, ColorCode/Anaglyphic film/RGB, Pulfrich film/TV/RGB, ChromaColor film/TV/RGB, and Shutterglass high speed film/TV/RGB.
Here, Film is usually 35mm or 70mm (IMAX) - 16MM or 8MM is possible as well (although color issues arise when a color system like anaglyphic 3D is used with 8MM and sometimes with 16MM), TV is minimally DIGIBeta with Polarized and BetaSP with ChromaDepth/Pulfrich, RGB is Harddisk-through-VGA-beamer (where the speed of the harddisk dictates need for compression-which is highly inadviceable).

Your budget and the projectional possibilities of the theatre will dictate the system you'll have to use.

Beware that people and websites who claim that 3DTV is a real option are referring to shutterglass (VR goggles) viewing of the screen only. Anaglyphic broadcast has been performed partially succesful in the past, but only the broadcast station can perform such a trick (this has to do with the full availability of bandwith with broadcasted television). Taped television signal is never going to work with the anaglyphic system. This applies to MPEG 1 and 2 (DVD) as well.
More about the tribulations of 3DTV in the next chapter.

Note on film formats: There's at least a dozen formats that were invented and used when 3-D hit Hollywood for the first time. In the beginning this meant dual strip (two films, two projectors) - resulting in many errors with projection. Later, single strip systems were developed, like the StereoVision 3-D or SpaceVision 3-D system - an over-and-under 35MM system - that needed only one projector and decreased the possibility of mistakes and difficulties with projection. But these systems, also, came in a dozen.
Because of the multiplicity of available systems, this page will stick to the widest available system of StereoVision 3-D and IMAX 3-D. Even so, IMAX uses a polarized and a shutterglass (explained below) version for its 3-D films. If just to add more possibilities to the stack.

The big color issue.

Some systems use colored images, others don't (where they use the colors for left-right eye separating or image depth).
If you want to show your film like, say, 'Terminator 3-D' does, you obviously are going to be home free when it comes to preparing the images, for those are going to be 'normal' in color, but arranging for the polarized projection hardware is going to be nasty (and let's not talk about the mega-heavy dual 65MM camera part).

Besides the encoding techniques, recoring is another issue. Although all encoding techniques can be applied with post-processing, photographing an image with two camera's or two lenses in one camera, like the human eyes do, ensures for the best 3-dimensional result.
Two lenses can also mean a special lens on one camera, with a beam splitter that directs the separate images to be printed on film in any possible separating way on one or two films.

35mm film is a great start, for its color representation is no barrier (like a PAL/NTSC tape).
The most widespread form of 3D film is that of polarized filmprojection. 3D film companies usually shoot and project in the StereoVision system; left and right are above eachother on one frame, resulting in an 1:2.4 image. An appropriate projector is needed to make these two images overlap on the screen at exactly the right height and width. As with anything in film, a lot of different systems exist to store the two images on one frame of film.
Like side-by-side anamorphic (VariVision), side-by-side rotated, or just on top of eachother.

These days, a festival that wants to show filmed stereoscopic imagery will usually transfer this film to DIGIBeta (sometimes resulting in out-of-sync problems with the presentation: the drop/non-drop issue applies), beamed with two projectors that are equipped with the different polarized lenses. Direct-from-harddisk (Usually MPEG-2 compressed) is another option with this setup.
Note the necessity of a silver screen to have the polarized light still enter the polarized glasses at the right angle and to compensate for the loss of luminance by the polarizing filters on the projector (and on the glasses).
This option is theatre only (prjection, screen).

Polarized is a 'two-lens' technique.

StereoVision Split Lens
3-D Projection System

For actual specifics of polarized 3D film projection requirements,
like screen material, measures and angle, projection distance and angle, light reqiuirements and audience placement, check out:

the official manual on StereoVision 3D system at
http://www.film-tech.com/manuals/STEREOVISION3DPRINCIPLES.pdf

VR means putting an LCD screen in front of each eye. So this means full color, but (sort of) half image resolution; the even fields of the Video/RGB signal go to the LCD screen in front of the left eye, the odd fields go to the LCD screen in front of the right eye. True enough, television and interlaced computer screens display one field every 50th of a second (on PAL, 60th on NTSC, even more on computer screens) anyway, but images are recorded and transmitted at 25 frames per second (with PAL, 30 with NTSC). This is done to ensure correct display of rapid movement, so displaying seperate fields on the left and right eye can be strenuous on the brain.
Shutterglass refers to the other way of filtering the left eye and the right eye image through electronic means; the look-through glasses close after each other every field (50th of a second). For this to work, the left image has to be stored on the even field and right image on the odd field. An infrared emitter has to tell the glasses when to open and close, syncing the shuttering with the field display.
Because of its titanic cost (in relation to fitting out a theatre) it's no option for independent filmers, though. Only themeparks connected to studios and multinationals presenting a new product line can opt for this system.
Videocamera's for 3D recording and add-ons like NU-View work with the shutterglass system.
Shutterglass works with Theatre display, Television and interlaced Computer Monitor.

VR and Shutterglass are a 'two-lens' technique.

Field-sequential - or interlaced - example

Detail of scanlines

A combination of Shutterglass and 70mm (mostly IMAX or Space-Vision) film projection is also possible. This technically sophisticated way of immersing a special venue audience in a 3D film uses a 70MM film running at 48 frames per second. The audience then has to wear shutterglasses that are triggered by infrared equipment, and black out the left eye and right eye after eachother at a rate of 48 frames per second. So the IMAX film has the left eye image and the right eye image stored after each other per frame. A dual strip version of this system exists as well (two seperate IMAX films, one for every eye).
This system is the Rolls Royce of 3D film projection, and everything but the setup and cost is perfect about it.
This option is not only projection only, it's IMAX theatre only, since it requires an IMAX 3D projector, an IMAX screen and IMAX shutterglasses reacting to IMAX infrared transmitters linked to the IMAX projector. Good luck on trying to build that yourself!

IMAX is a 'two-lens' technique.

IMAX MKII reel units threaded in a 3D configuration

Anaglyphic steroscopics is a close second when it comes to separating left and right image, and being able to present depth.
Pitfall is the premise of the separating of the images through a red image for left and a blue image for right, overlapping on the screen (a purple or grey image with red and blue edges resulting). This means the film is going to be perceived as greenish gray by the viewer, so colored images are not possible.
This doesn't have to be a problem when your 3D film is black&white anyway - like a 50ties style movie, a movie focussing more on content, or an art film in some sort. Use the look as an addition to your film.

Added to this, the palette of both red and blue can only range from black to 50 percent red and blue (true red and blue). So whites are out of the question. This is, because the colored filters in the glasses can only filter out up until that 50 percent red or blue. When anaglyphic imagery includes whiter color values, ghosting (cross talk) will certainly happen.
This, again, sounds more dramatic than it looks, for image perception is always a relative experience; the brain always looks within an image in the context of its limits. So for the viewer, the 50 percent of the available palette will look like the full palette.

There is, still, a way of using a noramlly colored image, with an added 3D effect for viewers who wear anaglyphic glasses.
In this 'colored', or semi-anaglyphic coding, the green image part (of RGB) is not discarded, but added in the blue -right- image. Overlapping Red -left- and Blue/Green -right- now display a 'normally' colored image. This way of anaglyphic coding is sometimes used for presentations that must also be pleasant to the eye without 3D glasses. Magazines like to do this. The 3D effect is likely to be harmed, though, as figures.

A plus is that a regular film (no special format) and only one projector/beamer is neccesary to present the image.
TV won't work (tape-wise) since its colorspace is too limited. More about this in the 3DTV chapter.
The anaglyphic option works in a treatre and on a Computer monitor. (Hence 3D movies on the internet are mostly anaglyphical ones) This is all due to the ability of Film and RGB monitors to keep colors correct and separated.

Anaglyphic is a 'two-lens' technique.

ColorCode is a spinoff of anaglyphics, using yellow and blue to separate the left and right image - RGB channel wise, yellow is red plus green. The resulting image is in color (the same way semi-anaglyphics uses all of the RGB colors), the image is on one Film (like anaglyphics), but the glasses are patented and impossible to get by though anyone else but their patent holders. Contact Sirius Film for the technology or NWave Pictures for the features in this format.
This option works in a theatre and on a Computer Monitor.

ColorCode is a 'two-lens' technique.

The fact that Anaglyphics use Red and Blue and ColorCode uses Yellow and Blue to separate left from right does mean that full color pictures in 3D will have a different optimal palette to be used. As figures, anaglyphics suffer from images with red and blue in them and ColorCode suffers from images with yellow and blue in them.
Here's a comparison of all the primary colors in a single color 3D picture.