<title>Information theoretic analysis of birefringent antialiasing blur filters in the presence of aberrations</title>

Abstract

Charge coupled-device imaging systems are often designed so that the image of the object field is sampled well below the Nyquist limit. Undersampled designs frequently occur because of the need for optical apertures that are large enough to satisfy the detector sensitivity requirements. Consequently, the cutoff frequency of the aperture is well beyond the sampling limits of the detector array, and aliasing artifacts degrade the resulting image. A common antialiasing technique in such imaging systems is to use birefringent plates as a blur filter. The blur filter produces a point spread function (PSF) that resembles multiple replicas of the optical system PSF, with the separation between replicas determined by the thickness of the plates. When the altered PSF is convolved with the PSF of the detector, an effective pixel is produced that is larger than the physical pixel and thus, the higher spatial frequency components and the associated aliasing are suppressed. Previously, we have shown how information theory can be used in designing birefringent blur filters by maximizing the information density of the image. In this paper, we investigate the effects of spherical aberration and defocus on the information density of an imaging system containing a birefringent blur filter.