Making a 3D movie has many challenges of its own. No producer or videographer sets out to produce 3D that is hard to see, but with the complexities of managing a two-camera 3D crew combined with the pressures of filming, problems arise. A platform that was installed at a certain point in time can easily go uncalibrated and problems will only become apparent in the post-production environment. Even if these accidents are avoided, there are inherent image issues generated by the geometry of the camera that must be addressed before post-production can begin in a creative sense.

Avoiding headaches

Professional 3D camera crews use high-quality lenses whose size and weight often require the use of mechanically complex mirror equipment. These provide the ultimate in shooting flexibility, allowing the interaxial centers, the distance between the centers of the lens, to be adjusted from zero to well above the measured distance between human eyes. They also allow cameras to converge, as our eyes do when looking at objects up close.

In these teams, the smaller cameras and lenses can be used effectively in a side-by-side mode with the minimum interaxial distance governed by the camera body and lens size. With these two filming formats, there is the possibility that artifacts will appear that will need to be addressed; however, planning your shot and setting up your cameras carefully can avoid a lot of headaches during publishing.

3D Postproduction

Early in the publishing process will be all the work required to set up the left and right eye sequences to minimize viewer discomfort. The list of necessary checks and corrections includes the following:

• Basic Orientation: The left and right frames may need to be flipped or tilted to be usable.
• Color Imbalance: Since we use separate imaging systems, we cannot guarantee that color balance, gains, and gammas will match.
• Basic Geometry: Correction of errors in the size and rotation of the camera axis. No two lenses are the same; this is especially true for zoom lenses that add additional complexity to basic geometry.

Correcting these problems will reveal the finer geometric problems of the keystone distortion created by the convergence of the cameras.

Your eyes can tolerate some pretty serious mistakes for a short period of time, but we are planning to produce a full show or nighttime viewing and leaving these issues uncorrected will cause headaches for your viewers and often they won’t know why.

The most common problems that cause discomfort are:

• Excessive depth budget, the depth range from the front to the back of the scene, causing the eyes to converge or diverge.
• The vertical disparities between the left and right eyes cause the eyes to twist as they try to make visual sense of the scene.
• Having the depth of the subject point changes rapidly in cuts, causing viewers to change their point of convergence continuously.

If you get any of these setting factors wrong, the movie might give the audience a headache, but having addressed them, we can move on to the creative task, which was much easier to achieve in 2D post-production.

3D post production is challenging, even with the best equipment available. Double the volume of data in two high-resolution streams must be handled synchronously and in real time. You want random access to any frame or clip at any time, with 100% reliability and a set of tools that will run smoothly from ingest to export.

You also need a team that allows you to move your edit between suites, but keeps everything in sync and on the stage you reached with your work.

Depth budget management

Before Stereo 3D, you never had to worry about the depth budget. What is the depth budget? They are the limits between negative parallax (in front of the screen plane) and positive parallax (behind the screen plane).

These limits are usually surprisingly small and can be expressed as a percentage of the screen width for television production (the big screen is a different matter), such as the depth budget of 2% positive parallax and 1% of negative parallax recommended by experienced stereographer Vince Pace and used by Sky TV in the UK. If you stay within budget for depth, with occasional short-term effects not exceeding 4% positive parallax and 2.5% negative parallax, eyestrain will be kept to a minimum and production will be comfortable to watch for two or three hours.

Be aware of the target screen

There are different issues to consider when publishing Stereo 3D, depending on the size of the screen, whether the finished piece is viewed on a television at home or on a big screen in the cinema. 2% of a television screen has a physical dimension much smaller than 2% of a movie screen. In the latter case, the 3D effect will be exaggerated and may cause the viewer’s eyes to converge or diverge unnaturally, causing tension.

Plan well and choose your publishing tools carefully and you’ll end up with a high-quality final product that is comfortable and enjoyable for your audience to see from start to finish.