The ubiquitous availability of fast computing platforms (such as multi-core CPUs and GPUs), the advances in algorithms and modern sensing hardware is resulting in imaging systems with significantly enhanced capabilities.
While applications such as SAR, computed tomography, seismic inversion are well known, they have undergone significant improvements (faster, higher-resolution, lower dose exposures[3]) driven by advances in signal and image processing algorithms (including compressed sensing techniques), and faster computing platforms.
The pinhole camera is the most basic form of such a modulation imager, but its disadvantage is low throughput, as its small aperture allows through little radiation.
Pinhole cameras have a couple of advantages over lenses - they have infinite depth of field, and they don't suffer from chromatic aberration, which can be cured in a refractive system only by using a multiple element lens.
In recent years much work has been done using patterns of holes of clear and opaque regions, constituting what is called a coded aperture.
The motivation for using coded aperture imaging techniques is to increase the photon collection efficiency whilst maintaining the high angular resolution of a single pinhole.
Light hitting the FZP will diffract around the opaque zones, therefore an image will be created when constructive interference occurs.
Random patterns, however, pose difficulties with image reconstruction due to a lack of uniformity in pinholes distribution.
An inherent noise appears as a result of small terms present in the Fourier transform of large size random binary arrays.
The design method for URAs was modified so that the new arrays were based on quadratic residues rather than pseudo-noise (PN) sequences.
The significant advantage behind CSI is that it is possible to design sensing protocols that capture the essential information from sparse signals with a reduced amount of measurements.
Because the amount of captured projections is less than the number of voxels in the spectral data cube, the reconstruction process is performed by numerical optimization algorithms.