The phenomenon of persistence of vision was described by ancient Greek mathematician Euclid, and rediscovered by many including Roman poet Lucretius, Isaac Newton, and Joseph Plateau. This biological quirk was to become the basis for early entertainment devices such as thaumatropes, phenakistiskopes, zootropes, culminating with the introduction of cinema by Thomas Edison and Auguste and Louis Lumière. By flashing a series of still images within a short period of each other, the human brain overlooks the missing in-between content and/or flicker due to the afterimages which persist on the retina for about one twenty-fifth of a second.
The Persistence of Shadow is designed to use twenty-first century technology to illuminate this concept by exaggerating the phenomenon while at the same time instilling a similar sense of wonder that nineteenth century audiences experienced while witnessing early cinematic technology. Using Eadweard Muybridge’s high-speed time lapse photographs of a galloping horse as well as Thomas Eakins’s study of human motion as inspiration, the piece takes the shadow-play of a participant as its source material and produces an instant high-speed time-lapse style sequence of images which persist briefly, lending the shadow a gently receding trailing edge as it moves.
The piece uses a motion detection software called EyesWeb. A performer standing in front of a white screen is captured by a video camera, which feeds the signal to a computer for further processing. The live video input feed is converted to grayscale and the darker areas are extracted using a threshold computation. These darker areas are processed, keeping the current version as well as blurred past versions which are set to linger for about a second before completely fading out. Before the image is output, it is inverted so that the silhouette is both black and mirrored, matching the performer’s motions. The final effect of having a shadow with a lingering trailing edge feels mesmerizing and dream-like to both performer and audience.
