  This paper presents innovative algorithms to efficiently compute erosions and
dilations of run-length encoded (RLE) binary images with arbitrary shaped
structuring elements. An RLE image is given by a set of runs, where a run is a
horizontal concatenation of foreground pixels. The proposed algorithms extract
the skeleton of the structuring element and build distance tables of the input
image, which are storing the distance to the next background pixel on the left
and right hand sides. This information is then used to speed up the
calculations of the erosion and dilation operator by enabling the use of
techniques which allow to skip the analysis of certain pixels whenever a hit or
miss occurs. Additionally the input image gets trimmed during the preprocessing
steps on the base of two primitive criteria. Experimental results show the
advantages over other algorithms. The source code of our algorithms is
available in C++.
