Multi-rigging for Live Stereoscopic 3D Shoots:

Producing an animated stereoscopic 3d movie is acknowledged to be a lot easier than shooting a live 3D movie. The primary reason being that a stereoscopic 3d “camera rig” can be completely controlled in any way imaginable, from setting inter-axial (horizontal distance between the left and right cameras lens midpoint), to animating the interaxial, and flight path of the camera. When seeing any of the newer Stereoscopic 3D animated movies from the likes of Dreamworks, Disney and others, we can’t help but notice the “roundness” of the 3D both for nearby objects and even mountain-scapes in the distance.

How is this done? For example, we all know that if we adjust the interaxial of a parallel (side-by-side stacked) 3D camera rig, or if we adjust the convergence or “toe-in” of the cameras to converge on the subject of interest in the fore to mid-ground of a scene, then distant buildings and scenery will look completely flat, or worse… will exhibit severe horizontal disparity, making the eyes diverge (go wall-eyed) and thus making it impossible to fuse the imagery. This may also lead to headaches.

One solution is to re-frame the entire shot, or to try and use really shallow depth of field so that the background is very…very de-focussed and would not tempt a viewer to try to resolve the background imagery. This of course is what any Director would want, and indeed is what movie story-telling is all about.

However, by it’s very nature, Stereoscopic 3d invites the user to look around a panoramic vista when presented.

Green screen Multirigging for live stereoscopic 3D (image (c) LA Times)

Multi-rigging for a Stereoscopic 3D CGI movie:

In a stereoscopic 3D CGI movie, to get proper roundness and to control excessive parallax (horizontal disparity), there is a trick. The CGI stereoscopic camera is first setup to render the background of the scene, with an appropriate interaxial setting. The foreground objects and characters are hidden from the render. Next the Stereo CGI rig is set-up to do the opposite. This way there is assured “roundness” of the entire scene, when composited together. One of the reasons that producing Stereoscopic CGI 3D movies is so easy.

2D to 3D as an easy fix?:

2D to 3D conversionists would quickly jump in and recommend the entire scene be shot 2D and then converted in post. We all know the bad rap that 2D to 3D conversions are getting recently. While there may be a few scenes that could benefit from such conversions, the “depth” of the scene is usually compromised in conversions.

Filling bigger “holes” after rotoscoping different layers in a 2D scene, is not easy and is one of the reasons 2D to 3D conversions are usually a bit flat looking, yet may be disguised as the “new and safe” 3D look that movies should have.

There is an argument and recommendation to shoot blank 2D plates of the scene (with the actors etc removed), so as to provide the missing “data” for the artists to fill in but even this is not without problems, as in live shoots dynamics change between what was shot during the “take” and what was shot for the blank plate. Examples are foliage, clouds moving etc.

Green Screens, Masking and Interaxial setting for Stereoscopic 3D Multi-rigging a Scene:

Take a look at the first image in this article (click for bigger image). There is virtually no depth visible on the buildings in the background, and they just appear offset deep into the screen.

Doing this exercise for Live Stereoscopic 3D needs careful planning with a stereographer, the director, DP and also a creative re-look at the screenplay and storyboard. In the first image above in this article, if there were a fight scene on the rooftops and we also wanted to see nice deep 3D in the background, a bit of careful planning and re-framing of the shot would make for a compelling and immersive stereoscopic 3D experience.

How would we go about getting a nice rounded look for the entire scene?

•First we would evaluate whether the scene actually calls for a deep 3D vista look. If this is an establishing scene in a movie, it would make sense to do so.

•If an action scene is being shot *and* the director wants the audience to also take in the entire panorama, it would also make sense to multi-rig for the shot.

After these factors are determined, a few methods can be employed:

•If the scene is just a panoramic shot as shown in the image above, Two versions of the scene can be shot, one with an interaxial separation of a few meters (of-course, not possible with a mirror rig) for the background. This would give excellent “rounded” 3D on the background. The foreground is then masked out in post, if it is a still shot, or a tracking shot would then have an animated mask again done in post.

•A new interaxial would be set to create comfortable 3D on the fore to mid-ground and a reverse mask used to clear out the background

•Both these “layers” would then be composited to give the final 3D scene.

By doing it this way, if we introduce live talent, say a fight scene on the rooftop, we could selectively blur the entire background in post, to guide the viewers eyes to the action in the foreground, *after* the full vista like 3D shot of the location is introduced to the viewers.

Lastly, we could use green screen either rigged at the actual location to shoot the fight scene (in the image above it would be just behind the second rooftop and block the rest of the background), or can be shot in a studio with matching inter-axial, focus and distances as setup when shooting the foreground 3D “layer”.

Establishing the 3D Geography of a scene:

This is an important consideration that most Directors and Cinematographers seem to miss out on – This is a 3D movie, so one needs to establish the “3D geography” of the scene for a more immersive experience, before directing the viewers attention to the on-screen talent or subjects. This will satisfy the audiences quest for 3D eye-candy and not make them want to look at the background during the ensuing action. This practice may reduce headaches from audiences trying to fuse semi-focussed surroundings and may help devote their full attention to the on-screen acting.

How this is achieved is a creative choice the Director has to make by planning the screen play and storyboard, and may not be suitable for every scene… but is a suggestion.