Towards normalized iconic indexing

Most of the existing pictorial indexing methodologies describe images with meaningful orientation. However, in many cases, more freedom in the filing of images with respect to the orientation is required since the visual information contained in them is independent of any orientation or simply should not be affected by possible erroneous storing, for example in the reverse direction. The authors define a mapping between images and indexes that satisfies the property of normalization. In particular, they deal with the problems of reversing and rotation of images, which represent the two fundamental manipulations in the 2D space. They present an indexing methodology based on the Indexed 2D C-string that satisfies the normalization requirement. Then, to obtain the rotation invariance, they introduce a system of polar axes that substitutes the Cartesian one, and totally inherits all the properties of orthogonal indexes. Finally, the authors define a structured index which represents the second level of normalization of an IDBS