A Study of Registration Methods for Ceramic Tile Inspection Purposes

This work presents a study of two image registration methods for ceramic tile inspection purposes. Tile registration is the first step in detecting surface faults when a ‘compare with a reference’ technique is used. The presented methods are based on edge detection techniques, used to extract the bounding rectangle defined by the tiles. They differ in the approach used to obtain this rectangle. The first method only uses a reduced set of border tile points, obtained with the minimum cross entropy thresholding algorithm, and fits them to straight lines by the least-squares method. The second method uses a general Hough transform approach that uses an edge map of the tile image. The geometrical transformation needed to carry out the registration is directly obtained using a simple geometrical mapping. Several experiments have been used to compare and select the method that offers the best results from the point of view of registration quality and computer time cost. The study is restricted to tile models with fixed decorative surface patterns.