Optimal filtering of solar images using soft morphological processing techniques

Context. CCD images obtained by space-based astronomy and solar physics are frequently spoiled by galactic and solar cosmic rays, and particles in the Earth’s radiation belt, which produces an overlaid, often saturated, speckle. Aims. We describe the development and application of a new image-processing technique for the removal of this noise source, and apply it to SOHO/LASCO coronagraph images. Methods. We employ soft morphological filters, a branch of non-linear image processing originating from the field of mathematical morphology, which are particularly effective for noise removal. Results. The soft morphological filters result in a significant improvement in image quality, and perform significantly better than other currently existing methods based on frame comparison, thresholding, or simple morphologies. Conclusions. This is a promising and adaptable technique that should be extendable to other space-based solar and astronomy datasets.