This paper presents a general framework to generate multi-scale repres
entations of image data. The process is considered as an initial value
problem with an acquired image as initial condition and a geometrical
invariant as ''driving force'' of an evolutionary process. The geomet
rical invariants are extracted using the family of Gaussian derivative
operators. These operators naturally deal with scale as a free parame
ter and solve the ill-posedness problem of differentiation. Stability
requirements for numerical approximation of evolution schemes using Ga
ussian derivative operators are derived and establish an intuitive con
nection between the allowed time-step and scale. This approach has bee
n used to generalize and implement a variety of nonlinear diffusion sc
hemes. Results on test images and medical images are shown.