Character Enhancement for Historical Newspapers Printed Using Hot Metal Typesetting

We propose a new method for an effective removal of the printing artifacts occurring in historical newspapers which are caused by problems in the hot metal typesetting, a widely used printing technique in the late 19^th and early 20^th century. Such artifacts typically appear as thin lines between single characters or glyphs and are in most cases connected to one of the neighboring characters. The quality of the optical character recognition (OCR) is heavily influenced by this type of printing artifacts. The proposed method is based on the detection of (near) vertical segments by means of directional single-connected chains (DSCC). In order to allow the robust processing of complex decorative fonts such as Fraktur, a set of rules is introduced. This allows us to successfully process prints exhibiting artifacts with a stroke width even higher than that of most thin characters stems. We evaluate our approach on a dataset consisting of old newspaper excerpts printed using Fraktur fonts. The recognition results on the enhanced images using two independent OCR engines (ABBYY Fine Reader and Tesseract) show significant improvements over the originals.