Tuesday, November 13, 2012

Image projection via caustics -- wow!

I just came across a method for projecting a monochrome still image that is stunning in both its simplicity and efficiency. Developed at École Polytechnique Fédérale de Lausanne (EPFL; Lausanne, Switzerland), the method relies on an acrylic projection "slide" that has nothing embedded within it and nothing printed on it, but instead has a surface shaped to be slightly uneven.

Place it at the right point between a reasonably small, bright light source and a wall, and an image appears. The image is formed from the "caustics" that arise when an optically smooth but rippled surface slightly and unevenly deflects light, producing lighter and darker areas (such as what you see at the bottom of a swimming pool on a sunny day).

Form the ripples in the right way, and you can project whatever image you want -- such as this image of Alan Turing, the British mathematician and father of modern computer science, shown in the light of an ordinary white LED.

Credit: (c) Alain Herzog

The surface shape to provide a specific image is calculated via an algorithm. Because this type of projection doesn't rely on absorption, the process is virtually lossless. Almost any transparent item could be made into a projector -- windows, display cases, architectural ornamentation, vases, glasses, jewelry, and so on.  See this EPFL Youtube video for more.

Researchers in EPFL's Computer Graphics and Geometry Laboratory showed working image-projecting caustic plates recently at the Advances in Architectural Geometry Conference in Paris. Contributors to the project include Mark Pauly (EPFL), Thomas Kiser (EPFL), Michael Eigensatz (Evolute; Perchtoldsdorf, Austria ), Minh Man Nguyen (WAO Architecture; Paris, France) and architect Philippe Bompas.

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