  The impulsive noise in astronomical images originates from various sources.
It develops as a result of thermal generation in pixels, collision of cosmic
rays with image sensor or may be induced by high readout voltage in Electron
Multiplying CCD (EMCCD). It is usually efficiently removed by employing the
dark frames or by averaging several exposures. Unfortunately, there are some
circumstances, when either the observed objects or positions of impulsive
pixels evolve and therefore each obtained image has to be filtered
independently. In this article we present an overview of impulsive noise
filtering methods and compare their efficiency for the purpose of astronomical
image enhancement. The employed set of noise templates consists of dark frames
obtained from CCD and EMCCD cameras working on ground and in space. The
experiments conducted on synthetic and real images, allowed for drawing
numerous conclusions about the usefulness of several filtering methods for
various: (1) widths of stellar profiles, (2) signal to noise ratios, (3) noise
distributions and (4) applied imaging techniques. The results of presented
evaluation are especially valuable for selection of the most efficient
filtering schema in astronomical image processing pipelines.
