Contour Line Recognition & Extraction from Scanned Colour Maps Using Dual Quantization of the Intensity Image

Automatic separation of the different layers of information in maps poses an immense challenge due to the heavy interconnectedness of these layers. This process is further complicated by the problem of mixed color pixels and aliasing induced by the scanning process. In this paper we present a new semi-automatic method to extract contour lines from scanned color images of topographic maps. In the proposed method, contour lines are removed from the image using a novel algorithm based on quantization of the intensity image followed by contrast limited adaptive histogram equalization. Unlike other interactive map feature extraction methods, in the proposed algorithm the user is involved in only one simple step of the feature extraction process and no prior knowledge about the underlying image processing steps is required. This method is incorporated as a .NET API plugin into ArcGIS (a commercially available Geographic Information System (GIS)) and its performance is tested on a number of graphics rich map samples of various sources.