The 515 doomed passengers and crew in this shot are both real
and computer-generated—trick question! All of the
passengers in this shot, from first class to steerage, were
created digitally, but the motion for the "synthespians" was
provided by live actors via
motion capture.
For this technique, the actors wear reflective markers at key
body joints, and surrounding cameras sense reflected infrared
light, recording their body movements in the computer. Later,
this motion is applied to the digital character. Fewer than 20
performers provided the motion for hundreds of virtual
characters in "Titanic."