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3D productions and stereoscopy
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3D productions and stereoscopy

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Preproduction. A 3D storyboard is a traditional storyboard with an extra column of drawings showing top or side
views of the set. The screen plane is drawn and the objects are plotted in. The result shows what will be in
front of, on, or beyond the screen, as well as how close to and how far away it will be from the audience. This is not only a big help at the set, keeping the depth continuity, but it is also a tool for making the overall depth script. Things “popping out” and ”rest areas” must be planned to support the storytelling.

Shoot. Good collaboration between the director, the cinematographer and the stereographer is essential.
The stereographer has a creative task, in addition to being a problem solver. ”Making it work” and ”avoiding eye strain” is only the beginning. The stereographer is responsible for calculating axial distances and convergence, working with the depth budget, making suggestions about framing / avoiding edge violations, minding the parallaxes, and so on. This is done with mathematical or intuitive knowledge of the 3D process. He/she should also be able to operate the 3D rig, but the time is better spent advising the director and DoP, leaving the adjustments to a rig operator.
The stereographer will also help out with polishing the final creation by recommending the use of floating windows, adjusting depth jump cuts, applying depth grading, and so on.

A 3D producer, or perhaps “3D production adviser” is a better name, is a person with extensive knowledge of both regular 2D production
and 3D production combined with a large helping of stereographic know-how. His/her main function is to translate 2D production in to 3D.
He/she should be able to tell what 3D related assets should be used throughout the process as well as the effect various 3D objectives will have
on the production budget. A 3D producer must have a holistic view of the whole production chain and be able to say how a change of plan during the shoot will affect the work in post. This is particulary important if CGI and compositing is involved. 
Get it right from the start. The most costly expression in the industry: ”We´ll fix it in post” has been taken to a new level when working in 3D.

The cameras must be a matching pair and must be able to genlock perfectly. The lenses must be matching pairs. The chip should be centered on the optical axis of the lens. The better the match between cameras and optics, the better the result. Remember that you are going to create the illusion of human perception. The chances are that you will do a better job with the proper gear.

A very rough and simplified approach to stereo 3D is that you need a pair of identical frames with an interaxial horizontal distance between them in order to obtain depth perception. To achieve this, you need a rig to set up the cameras. The calibration has to be done prior to each shot or scene. The two frames must be aligned both horizontally and vertically. The interaxial distance between the cameras has to be adjusted for each scene or shot in order to obtain the expected depth.
As a rule of thumb it would be true to say that the interaxial distance varies in direct proportion to the distance of the subject from the camera.
The closer the subject, the smaller the interaxial distance. The further the the subject the larger the distance.

When shooting at long distances, a parallel mount rig can be used. When shooting at short distances, you might need to get the optical axes so close together that the physical body of the camera or lens makes this impossible in a side-by-side mount.

This is why you need a beam splitter / mirror rig. Essentially, one camera is mounted at 90 degrees to the other. One camera shoots through the mirror and the other shoots the reflection. This enable us to adjust the optical axes so that they are so close together that zero parallax can be obtained. When moving in to macro shots, you need millimetres of axial distance.

Post. Technically, if the pair of frames contains different information, other than the interaxial, there is a potential problem. The brain attempts to make sense of the two different impressions of what it “knows” is the same image. Trying to fuse the two different images together will not succeed entirely and there is a risk of developing eye strain or worse. All miss matches must be evened out. For example, miss-alignment, flares, focus, exposure, zoom, grading, and so on. must all be identical in the two frames.

There is also the matter of matching two scenes in a cut. Convergence jumps can be very painful and you have to consider manipulating the parallax or perhaps using a fade to even out the cut. These creative decisions might require discussions with the rest of the creative staff, especially if roto or paint is applied to the scene. All this takes time.

Perception in 3D is about 300% higher than the same footage in 2D. This is one of the fundamentals in making the 3D experience attractive to the audience. However it also means that the level of technical perfection must be much higher. You can not get away with all the "cheating" you are used to in 2D. An effect you apply might require up to ten times more work to be accurate.