Alternative Image Description Techniques

Abstract

There is a variety of techniques that have been proposed in multimedia information systems area for shape representation [31, 41, 53]. Examples of those techniques are Fourier descriptors method (FD) [31, 41, 75] (based on objects’ shape radii) and grid-based method (GB) [50, 77] (based on chain codes). They were used in some commercial systems [53] and as a basis for different comparison studies in [50, 53, 77, 78]. In addition, a new method based on a new^r indexing technique (i.e., Delau-nay triangulation—DT) was proposed in [90]. With Delaunay triangu-lation, the shape features used are invariant under uniform translation, scaling, and rotation. However, with Delaunay triangulation, histogram--based representation is not very discriminative and is not unique, i.e., objects of different shapes may have the same feature point histogram representation. Also, choosing a histogram with a small number of bins provides less discriminating ability. Both Fourier descriptors and grid-based methods are variant to translation, rotation, and scaling. Therefore, shape signatures obtained for the same object with a different orientation in space or with a different scale will be different. Hence, given the shape signature of an object, a normalization procedure is required to normalize the object such that its boundary has a standard size and orientation.