A milestone in formally defining caricature was Susan Brennan's master's thesis[5] in 1982
. In her system, caricature was formalized as the process of exaggerating differences from a mean face. For example, if Prince Charles has more prominent ears than the average person, in his caricature the ears will be much larger than normal. Brennan's system implemented this idea in a partially automated fashion as follows: the operator was required to input a frontal drawing of the desired person having a standardized topology (the number and ordering of lines for every face). She obtained a corresponding drawing of an average male face. Then, the particular face was caricatured simply by subtracting from the particular face the corresponding point on the mean face (the origin being placed in the middle of the face), scaling this difference by a factor larger than one, and adding the scaled difference back on to the mean face.