MODELS OF IMAGES AND IMAGE OPERATIONS - Fundamentals of Three-Dimensional Digital Image Processing - page 23

Fig. 2.2. Digitization of signals and images.
2.2.3 Three-dimensional images
In this section, we will address 3D images.
A 3D continuous image is defined by a scalar (real) function of three
variables f ( x, y, z ), where f represents a characteristic value at a point ( x, y, z )
in 3D space.
A 3D continuous image is digitized in the same way as the 2D case; that
is, a function f is sampled at points of a cubic ordered array (3D grid or
3D lattice of sample points). Otherwise, the 3D space is divided into a set of
small cubic cells, and the value of the function f averaged over each cube is
assigned it . Hence, the cube is called volume cell or voxel instead of a pixel in