Surface representations for 3D face recognition

Abstract

For long, face recognition has been a 2D discipline. However, 2D face recognition has shown to be extremely difficult to be robust against a.o. lighting conditions and pose variations (Phillips et al., 2003). At the same time, technological improvements are making 3D surface capturing devices affordable for security purposes. As a result of these recent developments face recognition shifts from 2D to 3D. This means that in the current state-of-the-art face recognition systems the problem is no longer the comparison of 2D color photos, but the comparison of (textured) 3D surface shapes. With the advent of the third dimension in face recognition, we think it is necessary to investigate the known surface representations from this point of view. Throughout recent decades, a lot of research focused on finding an appropriate digital representation for three dimensional real-world objects, mostly for use in computer graphics (Hubeli & Gross, 2000; Sigg, 2006). However, the needs for a surface representation in computer graphics, where the primary concerns are visualization and the ability to process it on dedicated computer graphics hardware (GPUs), are quite different from the needs of a surface representation for face recognition. Another motivation for this work is the non-existence of an overview of 3D surface representations, altough the problem of object representation is studied since the birth of computer vision (Marr, 1982). With this in mind, we will, in this chapter, try to give an overview of surface representations for use in biometric face recognition. Also surface representations that are not yet reported in current face recognition literature, but we consider to be promising for future research – based on publications in related fields such as 3D object retrieval, computer vision, computer graphics and 3D medical imaging – will be discussed. What are the desiderata for a surface representation in 3D face recognition? It is certainly useful for a surface representation in biometric applications, to be accurate, usable for all sorts of 3D surfaces in face recognition (open, closed. . . ), concise (efficient in memory usage), easy to acquire/construct, intuitive to work with, have a good formulation, be suitable for computations, convertible in other surface representations, ready to be efficiently displayed and useful for statistical modelling. It is nevertheless also certainly necessary to look further than a list of desiderata. Herefore, our approach will be the following: we make a taxonomy of all surface representations within the scope of 3D face recognition. For each of the of the representations in this taxonomy, we will shortly describe the mathematical theory behind it. Advantages and disadvantages of the surface representation will be stated. Related research using these representations will be discussed and directions for future research will be indicated.