Easy Aerial Stereo 3D shooting

2D for 3D – or – The Pulfrich effect.

Shooting 2D for 3D will probably become industry terminology soon enough, just as ‘shooting dry for wet’ or shooting day for night are already established practices in modern film making.

Thanks to a certain scientist, Carl Pulfrich, who demonstrated the phenomenon also know as time multiplex in stereoscopic 3D circles, this trick of the trade has been used to some degree in the past by stereographers who know how to work within the limitations of this technique.

In very basic terms, if a subject is shot with a camera in steady orbit around it, at any given point in time there will always be a unique view-point of the subject recorded by the camera. This is also true if the camera is stationary and the subject itself is rotating. Using the time-multiplex (pulfrich) principle, two unique views can be extracted from such a scene, that will offer the two needed viewpoints as seen or recorded by typical stereoscopic 3D cameras.

The method to extract the second viewpoint is to use two copies of the same video and delay one of these by a certain number of frames for the desired depth effect.

click to view in 3D on Youtube, here. the original 2D video is from Youtube Channel ConradSh451

Helicopter aerial photography in 3D made easy:

In a feature film being made in 3D, the above method can be very effectively used with just a little preparation and not needing as much pre-planning as would be necessary if a real Stereoscopic 3D rig was to be employed.

With a real 3D rig there would be a large interaxial distance sometimes as much as 2 meters or more needed between cameras, and associated cabling to control both rigs, depending on the height of the aircraft or helicopter, and distance to the subject being shot. Other issues such as miniaturizing (hyper stereo) , lens flares affecting only one camera etc, would need to be worked out as well.

Shooting 2D for 3D however, is not without faults, and the astute Stereographer would know all the caveats in this short cut method of doing 3D. It is the intention of this article to make new stereographers aware of the pros and cons of this approach, as along with the easiness comes a few rules that should not be broken. Ignoring these rules can lead to eye-strain, nausea and headaches in audiences.

Shooting 2D for 3D; The Approach:

• The Pilot of the aircraft must as far as possible be able to maintain a perfect elliptical orbit at consistent vertical height
• Weather conditions should be optimal so that wind drag is taken into consideration, as with vibration etc. These are similar when shooting with 3D cameras as well
• Consistent speed should be maintained when orbiting the subject.
• Long shots using this method should be avoided, so as to prevent audience dizziness or dis-orientation by watching such scenes for longer durations.
• Framing should be done so that there is no distinct objects or Subjects in the scene that show vertical movement. For example no Person standing on a mountain cliff jumping up and down waving at the sky. This will create irreparable harm due to temporal errors (one “eye’s” view will have the hand at a certain position the other eye’s view will be different when extracting the footage)

Of all the considerations, the most important is the last one mentioned above. There has to be absolutely no Vertical movement in the scene of either the camera or the subject(s).

Shooting 2D for 3D: PostProduction:

After the regular 2D video has been captured, back at the post production desk, one of the first things to do is lay out two identical copies of the video in compositing and VFX software such as After-Effects or Nuke.

Next comes a vertical stabilization pass done to remove any vertical movement or jitter that may have occured with the camera. Once this is done, the tracking data is simply applied to the other copy of the video. More elaborate stabilization on both the X and Y axis can be applied for consistency, when working with an experienced VFX artist.

Then comes the desired offset to be applied to one of the copies of the video. This is done by either advancing the copied video layer by a few frames depending on the scene (This is where a Stereographer’s input and experience is in-valuable) or by applying the frame advance to the other video layer depending on the direction the aircraft was moving (clock wise or counter clock wise orbit).

At this point the 3D effect will be visible when both videos are played back either in anaglyph or full color 3D modes depending on the preview system available at the post production facility.

Establishing Shots in Feature Films:

In a Feature Film a 10 second establishing shot of the Castle on the mountain-side such as shown in the example above would save quite a bit of money, logistics and sweat equity if using the Shoot 2D for 3D approach. Using 10 to 15 seconds is perfect for a feature film, before cutting to another scene. Longer stereoscopic 3D aerial shots are best done the proper way – With a Stereoscopic 3D camera.

The example done above was completed in less than 5 minutes (it does show some side to side jitter that needs correction). If viewed with Angalyph 3D settings in Youtube and without the glasses, the moving black frame on top and below shows the stabilizing that was done in After Effects. The first frame shows how the frame shift was applied (when watching in anaglyph it shows one eye only…red)

This is a great way to use already existing Aerial Photography most notably, extracting 3D from 2D Stock footage.

For instance how much planning and cost would be saved by converting these Aerial Stock Footage shots?

Food For Thought:

Are there many such scenes in the movie Titanic? If  yes, would it make for easier conversion?

Read a related article : Easy 2D to 3D Conversions…Here.