On the detection of cracks in photographic prints

A method for the detection of cracks in old paper photographs is presented. Cracks in photographic prints usually result from a folding of the paper support of the photograph; they often extend across the entire image, along a preferred orientation. A first clue we exploit for crack detection is the fact that old prints have a characteristic sepia hue, due to aging and to the type of processing used at the time; a break of the gelatin exposes the white support paper; likewise, a break of the paper causes a black region in the digitized image. Thus, cracks are usually achromatic; this fact can be used for their detection on a color space with an explicit hue component. A series of parallel microcracks that run along the direction of a main crack usually result as well; even though the gelatin may not be broken, the folds corresponding to these microcracks cause a set of image discontinuities, observable at a high-enough resolution. In an interactive process, the user indicates the ends of the crack on the frame of the photo and the algorithm detects the crack pixels. In addition to color, the algorithm uses a multidirectional, multiresolution Gabor approach and mathematical morphology. The resulting method provides crack detection with good performance, as evidenced by the corresponding Receiver Operating Characteristics (ROC) graphs.