Stereo Renders

Basic setup for stereo rendering

Rendering a choreography in stereo is difficult because it is an exercise in transposing a virtual world into reality. To do it right, it is necessary to take into account the difference in scale between the models and the reality, some parameters from the reality, how the resulting image will be viewed and the effect expected.

Scaling the reality

All measurements and calculation described below are based on the assumption the the models are modeled at the same scale as the real thing they represent. If the scale is different than the reality, then the measurements needs to be scaled appropriately.

For instance, lets suppose that a model of a superhero designed to be 6 foot high is modeled as a 60 foot high. Then the PD as well as all the viewing pyramid measurements described below needs to be scales by 10 also.

Some parameters from reality

The first parameter taken from reality is the distance between the eyes. This is called "pupillary distance" or PD for short by the optometrists. This distance range between 5.5cm to 7.5 cm for an (north-American) adult with an average PD of 6.5cm (about 2.5 inches).

Another parameter taken from reality is how the resulting image will be viewed. Lets suppose that the resulting image is designed to be viewed on a XGA computer screen as a wallpaper. At this resolution, we can expect the screen diagonal size to be 17 inches which means approximately 32cm wide by 24cm high. The screen is expected to be viewed at a distance of 60cm. If we want to mimic the way the visual system would see the stereo image if it was placed into this virtual world, we must think of the viewing pyramid as a window into this virtual reality.

Transposing reality into virtuality

After enabling the "stereo" check box in the Output pannel of the camera attribute in the choreography, those measurements may be transposed into the camera as follow :

Enter 6.5cm into the Eye Spacing property of the Stereo pannel and enter 60cm (the expected distance from the viewer to the screen) into the Frame Distance property of the Stereo pannel.

Enter 66 into the Focal Length property of the Attributes pannel.

The Focal length determine the viewing angle. Fortunately, it is not necessary to revert to any trigonometry in order to compute the focal length. The formula is simply

FocalLength = ViewingDistance / ViewingWidth * 35

Note that the number 35 is a constant I found while working with different focal length distance within AM. Such a constant would have different values within other 3D applications.

From the measurements above, the Focal Length = 60 / 32 * 35 = 65.625.

Results

Rendering the scene in stereo using those parameters will produce an image that will look and seems to be at the right scale when viewed with the conditions specified. 

For instance, if we where to render a scene using those parameters where a character is framed as a medium shot, the volume of the character would appear real and solid and the character would appear to be floating 250cm behind the computer screen. This corresponds exactly to reality if we where to look at a real person in medium shot from a such small window.