Video and film restoration using mathematical morphology

All those who have visited the cinema will be familiar with the problem of film dirt, i.e. dark artefacts corrupting the images viewed. It is obviously desirable to remove this corruption, especially if one wishes to sell digital versions of the film. This type of film dirt is only present in the luminance fields of the sequence. So, in order to remove this corruption, a suitable filter is applied only to the luminance field of each frame in the sequence. However, it is necessary to determine exactly which filter to use. In this paper we consider the class of soft morphological filters (Koskinen and Astola 1994). But, it is still necessary to determine which, out of the whole class of soft morphological filters, is the optimal filter for this application, i.e. the filter that will be able to remove most noise whilst preserving the underlying structure. This topic is discussed.