The modeling of diffuse objects is called Particles
System5,6. The representation of particle systems is
different from the normal representation of images in three
key points. First, an object is not represented by a set of
geometric primitives that define the boundaries of the
surface such as polygons or triangles, but as a great
accumulation of primitive particles that define its volume.
Second point, a particle system is not a static entity as the
particles change shape and move with the passage of time.
The new particles are "born" and old particles "die." Third
point, an object represented by a particle system is not
deterministic because its shape and appearance are not
completely defined, however stochastic processes are used
to create and change the shape and appearance of the
object.