What is the Pulfrich Effect?
The Pulfrich effect is a psycho-optical phenomenon that was documented by Carl Pulfrich in the early 20th century. It is due to the difference in the speed of perception according to an object’s luminosity. The Pulfrich effect is thus perceptible only in the case of moving objects. For example, look at the movement of a pendulum swinging from left to right. If you cover one eye with a piece of dark glass you will see the lateral swing seconded by a movement in depth, as if the pendulum were oscillating in a circle rather than a plane. The darker the filter, the more pronounced the effect becomes.
If the filter is over the left eye, the moving object seems to be in front of the plane of the screen if it moves to the left and behind the plane if it moves to the right. The explanation is simple: The presence of a dark filter over one eye produces a lag in the perception of the scene coming from this eye. The left eye thus sees the pendulum a split-second later, and that causes a horizontal disparity with respect to the right eye. The brain interprets this difference as an interocular parallax and deduces a depth proportionate to the speed and direction of the moving object. Motionless objects are not affected.
The New Trick
As pulfrich glasses are not so common, Katsuhiko Inoue, a retired physicist from Osaka University, added red/cyan color correction to the popular Pulfrich video “Demonstration of the Pulfrich Effect: NC State Fair“. Watch the result with your good old red/cyan glasses here below.
The Pulfrich 3D viewable with Red/Cyan glasses
Explanations by Inouek3D:
“I did mash up to L/R side by side stereoscopic video by means of embedding the Pulfrich filter into the left clip to make stereoscopic pair together with original R clip. In this implementation the viewers do not need any Pulfrich glasses to view the Pulfrich video, ordinary stereoscopic 3D viewing method e.g. passive and active 3D monitor or 3DTV, free viewing (Cross and Parallel) and anaglyph etc. Other potential advantage will be the ND [Neutral Density] filter can be applied to both L and R clip adaptively to the opposite moving direction scenes.
Patterned ND filter may be applied to the video at the situation where camera is moving straight forward to the vanishing point. A lot of optimization will be necessary to apply this method to the real motion scenes. Viewing note: View first far side people (moving left to right) will help you to perceive the total depth of this Pulfrich stereoscopic 3D video. I would like to acknowledge the author of the original Pulfrich video I was inspired to make this version.“
This is a re-post from here by Benoit Michel. For more information on the Pulfrich effect -see chapter two of Digital Stereoscopy by Benoit Michel; the book is available in French here and soon in English and Korean on Amazon and other online bookstores.