Coded aperture

Coded Apertures or Coded-Aperture Masks are grids, gratings, or other patterns of materials opaque to various wavelengths of light. The wavelengths are usually high-energy radiation such as X-rays and gamma rays. By blocking and unblocking light in a known pattern, a coded "shadow" is cast upon a plane of detectors. Using computer algorithms, properties of the original light source can be deduced from the shadow on the detectors. Coded apertures are used in X- and gamma rays because their high energies pass through normal lenses and mirrors.