Blotches correction and contrast enhancement for old film pictures

A complete system for old picture restoration is described: in particular, a frame alignment method, a simple deblotching algorithm and a nonlinear approach for contrast enhancement are proposed. The frame alignment uses a global motion compensation, with a logarithmic search for the correction vector. The blotch removal step consists of two stages. Blotches are first detected using two suitable morphological operators; the resulting pixel maps are merged and then validated using an estimate of the motion. Secondly, a multilevel median filter is used to replace sets of pixels identified as blotches. For contrast enhancement we use a rational unsharp masking technique which is able to effectively treat the high resolution images. To comply with the film properties the sharpening operator acts strongly in the dark regions and weakly in the bright ones. It can also reduce noise in homogeneous areas.