In the modern world, we need high-resolution images for many applications, but the resolution of the imaging system can be degraded due to many factors, mainly the optical and geometrical components. The resolution limit for the optical system is set by diffraction, called diffractive superresolution. The resolutions of the imaging system are reduced not only by the optical components, but also by the geometrical components, which we call charge couple devices (CCDs). A CCD is an array of infinitesimal pixels (photodetectors). The resolution limit set for the imaging system due to the shape, size, and pitch of the sampling pixels (i.e., the distance between the centers of the consecutive sampling points) is called gometric superresolution. We are trying to overcome resolution limitations put on the imaging system by the CCD. With this technique we consider an infinitesimal delta function for the pixels of the CCD and an optical rectangular mask in which each pair (line/mm) has a specific width to make the optical rectangular mask more practical. Here we consider a 4-f optical imaging system; the spectrum of the input object falls on the optical rectangular mask, which is located at the back focal plane, and an inverse Fourier transform provides the image of the input object at the CCD plane. This image is sampled by the infinitesimal point pixels of the CCD and the Fourier transform gives the multiple spectrum of the input object overlapped to half of the next spectrum on either side. Then the overlapped spectrum is multiplied with the decoding optical rectangular mask (the same as encoding optical rectangular mask) that makes the overlapping effect disappear, and a train of completely separated spectrums is obtained; filtering gives a single spectrum matched to the spectrum of the original input object.
Resolution of any image taken by CCD camera is generally lower in resolution in comparison with original object.
Assuming the imaging system as diffraction limited - the major component responsible for this resolution limitation is
the pixel geometry in CCD. The area, shape of pixel and distance between them (inter-pixel spacing) together contributes
in reduction of the resolution of the final electronic image. A number of techniques have been reported in the literature to
overcome this geometric resolution limitation. We have proposed a novel geometric superresolution technique in which a
CCD-mask is displaced over CCD-plane by one pixel in subpixel steps - both in x and y directions. The resultant
processed superresolved image is improved in resolution by the subpixel steps factor. Simulation results in 2D have been
presented which shows improvement in resolution. This superresolution technique can be applied to microscopy, medical
imaging, satellite imaging and astronomy.
High-resolution imaging can be achieved by optical aperture synthesis (OAS). Such an imaging process is subject to aberrations introduced by instrumental defects and/or turbulent media. Redundant spacings calibration (RSC) is a snapshot calibration technique that can be used to calibrate OAS arrays without use of assumptions about the object being imaged. Here we investigate the analogies between RSC and adaptive optics in passive imaging applications.