Abstract Muscle Action Procedures
for Human Face Animation

N. Magnenat-Thalmann, E. Primeau, and D. Thalmann
Visual Computer, 1988

Abstract

A new way of controlling human face animation and synchronizing speech is proposed. It is based on the concept of abstract muscle action procedure (AMA procedure). An AMA procedure is a specialized procedure which simulates the specific action of a face muscle. This paper describes the new technique and presents a methodology for animating the face of synthetic actors based on three levels: the AMA procedure level, the expression level, and the script level. The role of multiple tracks is also emphasized. Practical examples are also explained in detail, based on the film Rendez-vous a Montreal with the synthetic actors Marilyn Monroe and Humphrey Bogart.

Summary

Muscle actions are simulated with abstract muscle action procedures. Each AMA procedure corresponds roughly to a muscle or bone structure. AMA procedures are not independent of each other, so the order of action is relevant. As human muscles are highly complex, the AMA procedures must simulate the same motion without imitating the complexity. The following is a list of the most important AMA procedures:

Number AMA Procedure Range
1 Vertical_Jaw 0 to 1
2 Close_Upper_Lip 0 to 1
3 Close_Lower_Lip 0 to 1
4 Compressed_Lip 0 to 1
6 Mouth_Beak 0 to 1
7 Right_Eyelid -1 to 1
8 Left_Eyelid -1 to 1
9 Left_Lip_Raiser 0 to 1
10 Right_Lip_Raiser 0 to 1
11 Left_Zygomatic 0 to 1
12 Right_Zygomatic 0 to 1
23 Move_Right_Eye_Horizontal -1 to 1
24 Move_Right_Eye_Vertical -1 to 1
25 Move_Left_Eye_Horizontal -1 to 1
26 Move_Left_Eye_Vertical -1 to 1
27 Right_Risorius 0 to 1
28 Left_Risorius 0 to 1
29 Move_Right_Eyebrow -1 to 1
30 Move_Left_Eyebrow -1 to 1

It is possible to animate a human face by manipulating the facial parameters using AMA procedures. However, these procedures should be considered low-level access. By combining the facial parameters obtained by the AMA procedures in different ways, we can construct more complex entities corresponding to the well-known concept of facial expression.