Seamline detection in colour orthoimage mosaicking by use of twin snakes

In the last step of the mosaic production chain. neighbouring and partly overlapping orthoimages of a scene are merged to one mosaic. This should be done in a way that the transition from one to another orthoimage cannot be seen. The production line of orthoimages consists of several steps, each of which can introduce a different appearance regarding geometry, radiometry and spectral properties to the resulting orthoimage. For mosaicking adjacent orthoimages. a path of lowest difference in a combination of criteria is searched in the overlap area of these images. The seamline is chosen along this path of maximum similarity. In this paper, criteria for such an optimal seamline in colour orthoimages are elaborated. The main requirements are on one hand high colour similarity of the images (mainly in hue and intensity), and on the other hand high texture similarity (in orientation and magnitude of image gradients). The specified criteria are formulated in the energy function of snakes. A snake is an active contour which moves through an image and changes its shape until a minimum of its energy function is found. We use two snakes that attract one another (twin snakes). In a hierarchical strategy, a proper seamline is delineated fully automatically. The potential of the method is shown with an example. (C) 2001 Elsevier Science B.V. Alt rights reserved.