Sensitivity Matrix Coded Aperture Imaging Method

The standard coded aperture imaging approach assumes: • sources at infinity; • isolated point sources in specific directions; • masks with flat power spectrum (except for DC); • thin masks free of vignetting; • collimation to block rays from " out of view " directions; • visible sources cast full cycle of mask pattern on detectors; • use of correlation with the mask pattern to generate an image. In practice, typically: • sources are not infinitely far away; • sources may not be point sources; • masks have finite thickness; • collimation may be undesirable or imperfect; • sources may project only a partial mask shadow on detectors. Using the standard correlation decoding method leads to artifacts in these circumstances. Some of these artifacts may be ameliorated using mask/anti-mask techniques. However, one can do even better. Also, when sources are not infinitely far away, an opportunity exists to gather more information by taking additional measurements using different positions for the detector array. This extra information may be useful for recovering additional parameters of the source distribution, such as distances to sources, or simply to provide finer resolution. However, the traditional mask correlation method does not provide an effective way of dealing with this new information, or with the departure from ideal conditions met in practical applications. Further, only a very small number of possible masks have the special properties required for correlation decoding. Only masks with certain number of elements are usable, and these have the property that they are approximately half open. With nearby sources, and multiple detector array positions, different mask arrangements may be preferrable, It may even be advantageous to have three-dimensional masks (e.g. rods at various distances from the detector array).