Imagine taking a picture, without a camera. If that sound ridiculous, it's because it is — but it's also exactly what a team of researchers from the University of Glasgow, UK, have been doing.
This picture wasn't created using two multi-pixel sensors like most 3D images — but with a technique called ghost imaging, which for the first time has been extended to work in three dimensions. Ghost imaging records images of objects by recording light that doesn't actually hit them.
It sounds weird, but a single-pixel sensor can rely on paired light sources — say, a split laser beam — to gather intensity information that is later computationally reconstructed into an image. New Scientists describes how the 3D technique works:
A projector shines hundreds of random computer-generated, black-and-white patterns on an object, while four single-pixel detectors record the amount of light reflected back. Patterns that happen to match the shape of the object reflect more light than those that don't. The computer weights each black-and-white pattern according to the intensity recorded by the detectors and overlays the results, so that a picture of the object gradually emerges. The 3D system's four detectors are placed above, below and on either side of the projector. These detectors measure slightly varying intensities of reflected light and create pictures with different shading.
The result, published in Science, turns out to be exactly the same as if an ordinary camera were placed where the projector sits and the sensors were replaced with light bulbs. The results sure look neat, but they could be useful, too — because of the indirect way in which the images are acquired, the researchers reckon it could be used for surveillance cameras of the future. [Science via New Scientist]