Image processing tools for fresco restoration

In this communication, we illustrate an enlarging and enhancing procedure adequate to provide the restorer with sufficiently detailed digital versions of frescos in the excavations of Pompeii and Hercolaneum, starting from the photographic prints taken and archived in the early thirties for documentation purposes. First, filtering is done to improve the quality of the input data by removing acquisition and digitisation noise. Then, enlargement is done by using bilinear approximation. Finally, enhancement can be accomplished. To enhance only edges, we distinguish in the enlarged image edge regions from nonedge regions. This goal is achieved by applying edge detection and by thresholding the computed edge image. The obtained binary image is used as a reference to apply edge sharpening onto the enlarged image, and so obtain the enhanced image as desired. Though designed for a specific application, our method is indeed rather general.