<title>Regularized multiframe restoration of Hubble space and ground-based telescope images with parallel implementation</title>

Abstract

The spherical aberration of the primary mirror of the Hubble Space Telescope (HST) has seriously reduced the sensitivity and degraded the resolution of images from the instruments. After the first period of observation, most of the astronomic researchers do not try to make photometric measurements on original or somewhat restored images, but they see the opportunity to take the better resolution of the HST to upgrade their ground-based images. From that point of view, the need of multiframe restoration methods appeared. This paper first of all shows the problem of multiframe image restoration methods by looking at several well known single-frame methods and their generalization. The problem of week radiation in astronomical images is modelled by poisson processes which is well known from positron emission tomography. The unconstrained maximum likelihood method for this class of problems leads to an equation that can be solved by an expectation maximization type iterative algorithm. A regularizing subband method is proposed that incorporates the multiframe problem in a single-frame scheme by a subband type solution. The filtering for the subbands incorporates the model inherent freedom. Taking the simplest case of ideal low- and high-pass filters, there is still the choise of the cut-off frequency. The low frequency band is taken from the ground-based telescope with its good photometric property, the high frequency band is taken from the HST with its good resolution property. A transputer based parallel implementation with an underlying message passing system will be shown as a time efficient solution of the algorithms.