Coded Aperture - Rationale

Rationale

Image formation, normally done at optical wavelengths by lenses and mirrors, must be done for non-focusable wavelengths via image modulation. The pinhole camera is the most basic form of such a modulation imager, but a single aperture mask can contain many holes, in one of several particular patterns, to improve the throughput for hard X-rays and γ-rays, for example. Multiple masks, at varying distances from a detector, add flexibility to this tool. Specifically the modulation collimator, invented by Minoru Oda, was used to identify the first cosmic X-ray source and thereby to launch the new field of X-ray astronomy in 1965. Many other applications in other fields, such as tomography, have since appeared.

In a coded aperture more complicated than a pinhole camera, images from multiple apertures will overlap at the plate or detector array. It is thus necessary to use a computational algorithm (which depends on the precise configuration of the aperture arrays) to reconstruct the original image. In this way a sharp image can be achieved without a lens. The image is formed from the whole array of sensors and is therefore tolerant to faults in individual sensors; on the other hand it accepts more background radiation than a focusing-optics imager (e.g., a refracting or reflecting telescope), and therefore is normally not favored at wavelengths where these techniques can be applied.

The coded aperture imaging technique is one of the earliest forms of computational photography and has a strong affinity to astronomical interferometry