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  Introduction | Depth Modulation | Publications and Articles  
 
 

DEPTH MODULATION

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 image.


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.


PERCEIVED SIZE

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 perspective.

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".