A Method for Image Local-Difference Visualization

As ancient documents are being digitized, systems for retrieving documents or images can now be found in digital libraries. With regard to illustrations, the content-based image retrieval is difficult and the user often needs to check visually the similarity of the retrieved images. This process is not entirely reliable since very similar images (impressions, ornamental letters) can actually be printed from distinct stamps. No other visualization method exists than the map of pixel- to-pixel gray level difference (PPDMap). We propose here a method that evaluates locally the differences and allows the user to visualize them. It is based on a local adaptation of the Hausdorff distance. Our method performance is successfully compared to the PPDMap and an expert difference evaluation assesses our method reliability.