Recentlyin the field of computer vision, there have been many attempts to obtain a symbolic shape description of an object by fitting simple primitives to the range data of the object. In this paper, we introduce the "BIoJ Jy Mode/' for automatically generating a shape description from range data. This model can express a 3D surface as an isosurface of a scalar field which is produced by a number of field generating primitives. The fields from many primitives are blended with each other and can form a very complicated shape. To determine the number and distribution of primitives required to adequately represent a complex 3D surface, an energy function is minimized which measures the shape dMerence between the range data and the "Blobby Mode!'. We start with a single primitive and introduce more primitives by splitting each primitive into two further primitives so as to reduce the energy value. In this manner, the shape of the 3D object is slowly recovered as the isosurface produced by many primitives. We have successfully applied this method to human face range data and typical results are shown. The method herein does not require any prior range segmentation. Keywords: blobby model, generalized algebraic surface, implicit surface, volumetric shape description, range data analysis, energy minimization, ray trac-ing< Permission k} copy without fee all m part of this material is granted provided that the copies are not made or distributed for dired commercial idvmtagc, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission nf the Assw]ation for Computing Machinery. To copy otherwise. or to republish, requires a fee and/or specific permission. In the field of computer graphics, modeling and rendering of 3D objects are both important problems. Regular shapes such as machine parts can be simply described. However, a large amount of numerical data is necessary to describe a smooth and soft object such as a human body. At present, designers obtain such descriptions by tedious manual methods. Recently, a new modeling method, which is called "Blobby ModeP[9], has been used to describe smooth objects. This method expresses a surface of an object ACM-O-897Yl -436-8/9 l/C07/0227 $W.75 227 SIGGRAPH '91 Las Veaas, 28 JuIv-2 Auaust 1991 as an isosurface of a scalar field which is generated from field generating primitives. Since the shapes of the primitives are blended with each other, it is possible to express the surface of a complicated object with a small number of primitives. However, because of the fusion of the primitives, it is very dMicult to design "B1o bby Models" manually and so an automatic method of obtaining "Blob by Models" of 3D objects is desired. In this paper we present a method for automatically generating a "B[obby Modef' of a complex 3D object, given a set of range data. The 2; D model obtained by a computer vision technique can be precisely described with a set of blended shape primitives. If the number of primitives is small, then...
