Editing Computer animation (section)

==Facial animation==
{{Main|Computer facial animation}}
The realistic modeling of human facial features is both one of the most challenging and sought after elements in computer-generated imagery. Computer facial animation is a highly complex field where models typically include a very large number of animation variables.{{sfn|Masson|1999|pp=110–116}} Historically speaking, the first [[SIGGRAPH]] tutorials on ''State of the art in Facial Animation'' in 1989 and 1990 proved to be a turning point in the field by bringing together and consolidating multiple research elements and sparked interest among a number of researchers.{{sfn|Parke|Waters|2008|p=xi}}

The [[Facial Action Coding System]] (with 46 "action units", "lip bite" or "squint"), which had been developed in 1976, became a popular basis for many systems.{{sfn|Magnenat Thalmann|Thalmann|2004|p=122}} As early as 2001, [[MPEG-4]] included 68 [[Face Animation Parameter]]s (FAPs) for lips, jaws, etc., and the field has made significant progress since then and the use of facial [[microexpression]] has increased.{{sfn|Magnenat Thalmann|Thalmann|2004|p=122}}{{sfn|Pereira|Ebrahimi|2002|p=404}}

In some cases, an [[Affect measures|affective space]], the [[PAD emotional state model]], can be used to assign specific emotions to the faces of [[Avatar (computing)|avatars]].{{sfn|Pereira|Ebrahimi|2002|pp=60–61}} In this approach, the PAD model is used as a high level emotional space and the lower level space is the MPEG-4 Facial Animation Parameters (FAP). A mid-level Partial Expression Parameters (PEP) space is then used to in a two-level structure – the PAD-PEP mapping and the PEP-FAP translation model.{{sfn|Paiva|Prada|Picard|2007|pages=24–33}}