The field of electroacoustic music has
witnessed many years of extensive exploration of aural spatial
perception. Research based on the separation and manipulation of
monaural and binaural cues resulted in an abundance of sound
spatialization techniques and approaches. Today the growing ubiquity of
visual 3D technologies gives artists a similar opportunity in the realm
of stereoscopic video. We now have the
ability to compose individual depth cues independently, a process I
refer to as depth modulation.
Depth modulation is a phenomenon unknown to real world experience. It
is however available to us in the visual realm through the direct
modification of visual cues using stereoscopic video, and in my opinion
this process shows great potential for artistic experimentation.
By changing the distance between cameras over time in a stereo image we can create
what I have termed direct
depth modulation. Direct depth modulation has two interesting effects on how one perceives the
PERCEIVED DEPTH AND DISTANCE
The first and most obvious is how it changes the perceived
distance of objects from the viewer. As the cameras move closer
together and stereoscopic depth cues fade, objects appear to flatten
towards the depth of the physical screen.
Objects in the background are drawn forward, objects in the foreground move back, and objects with
perceivable depth get flatter.
In fact, if this process continues, stereoscopic depth cues are reversed. Objects once perceived to
be in the background now appear to "move" forward. This may create a conflict between
stereoscopic and monocular depth cues, so care must be taken when choosing images.
Along with changes in perceived depth, depth modulation also
influences the perceived size of objects in the image. This effect is
created by the clash between two depth cues, binocular disparity and
As an object moves towards the viewer it fills a greater portion of
the field of view, and as it moves away from the viewer it fills less of
the field of view. This is an effect known as looming.
When objects move towards and away from the viewer, perspective and
binocular disparity are properly synchronized, matching our real world
expectations. However when only depth modulation is applied with no
changes to the objects themselves, only binocular disparity is affected.
Perspective is unchanged. Even while the object appears to be moving
backward or forward in space, there is no looming.
This creates the perception that the size of the object changes as the stereoscopic
depth cues change. When the distance between cameras increase, depth cues become more pronounced.
Objects in the forground appear to move towards the viewer while objects in the background
appear to move away from the viewer. However, because there is no looming, the size of
the object appears to change. Objects in the foreground appear to shrink while objects
in the background appear to grow.
Because these experiences lie outside our normal daily experiences, it is difficult for
us to perceive these changes as they happen. Viewers often describe a moment of surprise
as these continuous changes in depth cues are suddenly "noticed".