First 3D Ghost Images From A Single Pixel
[Philip Lelyveld comment: I'm having trouble understanding how the recording element is a "pixel" as opposed to a volume.]
Ghost imaging is the extraordinary technique of bouncing a laser beam off an object and making high quality images from the reflected light using a single pixel. This single pixel records many data points which must be stitched together to create the image.
But there is no scanning involved (which would be equivalent to taking an ordinary picture very slowly).
Instead, the data from the single pixel is compared against the intensity of the original laser beam, which must be randomised by passing it through frosted glass. Then any correlations between the original and reflected beam reveal information about the object in the image.
It is these correlations that physicists use to assemble the picture, known as a ghost image.
That may sound rather fiddly and time consuming but it is actually hugely efficient.
See the full story here: http://www.technologyreview.com/view/510411/first-3d-images-created-with-single-pixel-sensor/