Discounting the joy of Pulfrich 3D

[P3D Scott Langill <slangill@xxxxxxxxx>]

In response to:

> Am I the only one that did not "discover the joy" of Pulfrich 3d and
> did not find it "amazing and effective effect" when seen for a first
> time? In my first Pulfrich experience I had to convince myself and
> the others around me that we were seeing 3d... -- George Themelis

     I wholeheartedly agree. In a sense you were seeing an illusion of
depth, but you were not seeing depth or 3D.

     The Pulfrich Effect utilizes a colored or shaded lens over one eye
to delay the signal from that eye to the brain. The delay is falsely
interpreted by the brain as representing two simultaneous views of the
same object displaced from one another spatially due to the presence of
depth in the object. The brain recognizes the signal as disparity
information of the sort used to resolve depth (i.e. in stereopsis). The
effect is wholly dependent upon movement (e.g. a pendulum was used in
the original experiments). Factors such as relative true depth or
apparent velocity (i.e. motion parallax) would perhaps interact with the
effect (as would other two dimensional cues to depth), but real movement
across the retina is necessary for the brains false resolution of
"apparent" disparity. Without movement there would be no sensation of
three dimensional depth perception. In other words, the faster the
movement the more the depth.

     Moving objects have depth, static objects do not, faster objects
have more depth, objects moving perpendicular to the observer's line of
sight have more depth than those moving angularly at the same real
velocity, and moving objects in the distance have depth even though
stereopsis is normally functional out to about twenty feet. This does
not bear much resemblance to the real world (despite what the 3D
Frequently Asked Questions File would lead you to believe).

     Two dimensional cues to depth can be very powerful, and as is the
case with most illusions of three dimensional depth perception, they
will interact with and can overpower three dimensional cues (such as
with distorted rooms of the mystery spot variety). It is important to
differentiate between perceived depth due to the Pulfrich Effect and
perceived depth due to two dimensional cues or stereopsis. Any
coincidence between perceived depth due to the Pulfrich effect and real
depth is (despite the ingenuity of television writers) accidental at
best. It is difficult to think of an appropriate analogy, even
colorization "depicts" true color. P.T. Barnum, funhouse mirrors, and
the aforementioned mystery spots do come to mind.

     The theatrical presentation of 3D began in 1915, the first
anaglyphic feature films (utilizing red green glasses) were created in
the 1920s and the first vectographic feature films (utilizing polarized
glasses) in the 1930s. The presentation of 3D on television has been
hampered by three limitations: the expense of specialized camera
equipment, the expense of providing glasses to a mass audience, and the
fact that traditional anaglyphic and vectographic product were
unsuitable for two-dimensional viewing. Commercially available 3d
cinematic processes suitable for two dimensional viewing (in both
anaglyphic and vectographic formats) have been available since the
1970s, but the attendant additional costs of filing and viewing
remained. Enter the Pulfrich Effect, no special cameras, inexpensive
dark and clear glasses, a suitable 2D appearance (with no "fringes" at
all), a promotable (albeit unreal and non-stereoscopic) "3D" effect, and
an accepting audience.

     It is unfortunate that a group as influential as the readers of and
contributors to the photo-3d mailing list and 3D Frequently Asked
Questions file are so enthusiastic about the use of the Pulfrich Effect
on television. It would seem apparent that bandwidth would better be
spent attempting to convince television networks and producers to use
the available and true stereoscopic techniques.

@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*@#!*
Scott W. Langill                                   Arbeit mach das leben
Special Edition          slangill@xxxxxxxxx        suesse, aber faulheit
Washington, D.C.                                 staerkt die gliederung.
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