Photos with shifting shadows come to life

2017-09-24 01:00:19

By Colin Barras Despite advances in image-capturing technology, photographs preserve an unchanging moment in time. Now a new zero power display breathes new life into still images by letting an image change in appearance through the day as the direction of the Sun’s light changes. Using the system, shadows in a still life can be made to move and lengthen just like they do in the real world, or the Sun could be made to move across the sky of a landscape photo. The technique could also be used to add an extra dimensionality to bill board displays, the system’s lead developer Martin Fuchs at the Max Planck Institute for Informatics told New Scientist. Fuchs’ team at Max Planck collaborated with Ramesh Raskar at the MIT Media Lab, Cambridge, Massachusetts. The researcher’s prototype device, which can be attached to a window, comprises three layers: a lens array at the rear focuses light onto a transparency film on which a photograph is printed; the light passes through and is projected onto a “diffuser” in front, where the image is revealed. When the Sun rises in the east, the projected image shows objects casting a long shadow to the west. As the Sun climbs towards midday, the shadow shrinks, before extending to the east in the evening. This is possible because the picture on the transparency is actually a composite image, constructed from several hundred photographs capturing the same scene throughout the day. All those images are combined into one, which is divided into thousands of hexagons a few millimetres across. Each hexagon shows how the light varies in that small part of the picture across the several hundred source images. The hexagon for an area brightly lit in half of the images but in shadow in the other half, is half light and half dark (see image, top right). Rather than illuminating the whole hexagon, the lens array focuses sunlight onto the same tiny point within each hexagon, thus projecting only one of the many source images onto the diffuser. Because the effect is purely optical, the shadows move in real time and the device requires no power (see video above). “If you print out a picture you only have a 2D representation,” says Fuchs. “With our process you can maintain some of the variety of three-dimensions.” It should be possible to improve the 3D effect, says Fuchs. Currently the device displays a different image depending on the direction of the light source, but his team is working on an alternate version that projects a different image depending on the viewer’s position too, as a hologram does. That could make portraits with eyes that follow the viewer around the room a reality. Doing that requires additional layers of lenses between the transparency and the diffuser,