The DEPTH Workflow - 3D Postproduction: Stereoscopic Workflows and Techniques - page 162

5.7.4 The Three Enemies of Depth
There are three mortal enemies of the illusion of depth and you should
try to avoid them to achieve maximum comfort. These are: maximum
positive parallax/disparity (farthest away point where an image starts to
be uncomfortable to look at), maximum negative parallax/disparity (closest
point, where you try to poke the eyes off your audience), and the sides of
the screen (where 3D goes to die).
• Maximum Positive Parallax/Disparity . The bad news about this limitation
is that it is not a constant. It is directly linked to the size of your screen.
Perfectly comfortable 3D viewed on a 46-inch HDTV can “rip your eyes
out” if you watch the same shot from the third row on a big cinema screen.
The reason for that is because you can only diverge your eyes just so much
to see far objects. If you want to be able to make 3D adjustments just once
and use it for many devices, be VERY conservative with your limits. Try
never to go over 1% of maximum positive parallax (0.75% - 0.50% if you
are going to a really huge screen). On the other hand, if you want to make
your depth as expressive as possible for different formats, then account
for some budget and time to make global adjustments of the i nal movie
for the different screen sizes. Rule of thumb: The smaller the screen, the
deeper you should go. Pop-out 3D usually works better in big screen
with dark environment. Deep 3D usually works better in a small screen.
• Maximum Negative Parallax/Disparity . People are way more tolerant of
negative parallax (in front of the screen) than positive. In this case, the
eyes can converge A LOT. Try not to over-do it. Also, bear in mind your
editing and the shots around your effect so you don't have big front-back
changes.
• Sides of the Screen. Occlusion (something that is in front of something
else) is the most powerful of all the depth cues. The reason is simple. If an
object A covers another object B, that means object B is behind object A.
End of story. Your brain knows exactly where in space the sides of the
screen are (Object A), and if you have something l oating in front of the
screen in negative space (Object B) and it gets cut by the sides, your brain
will kill the illusion right there. The basic rule would be to try to avoid
the edges as much as you can! If the object moves through the edge fast,
it might not be too distracting and it could be okay. (Review it, show it to
several people and check their reactions.) But sometimes it is impossible
to avoid the sides, either because you can't push your depth any more
due to a positive limitation, or because you will harm the edit and the