Evaluating the Perceptual Realism of Animated Facial Expressions Christian Wallraven, Martin Breidt, Douglas W. Cunningham, Heinrich H. B¨ ulthoﬀ Max Planck Institute for Biological Cybernetics, T¨ ubingen, Germany The human face is capable of producing an astonishing variety of expressions—expressions for which sometimes the smallest diﬀerence changes the perceived meaning considerably. Producing realistic-looking facial animations that are able to transmit this degree of complexity continues to be a challenging research topic in computer graphics. One important question that remains to be answered is: When are facial animations good enough? Here we present an integrated framework in which psychophysical experiments are used in a ﬁrst step to systematically evaluate the perceptual quality of several diﬀerent computer-generated animations with respect to real-world video sequences. The ﬁrst experiment provides an evaluation of several animation techniques, exposing speciﬁc animation parameters that are important to achieve perceptual ﬁdelity. In a second experiment we then use these benchmarked animation techniques in the context of perceptual research in order to systematically investigate the spatio-temporal characteristics of expressions. A third and ﬁnal experiment uses the quality measures that were developed in the ﬁrst two experiments to examine the perceptual impact of changing facial features to improve the animation techniques. Using such an integrated approach, we are able to provide important insights into facial expressions for both the perceptual and computer graphics community. Categories and Subject Descriptors: I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism— Animation; J.4 [Computer Application]: Social and Behavioural Sciences—Psychology General Terms: Experimentation Additional Key Words and Phrases: Evalution of facial animations, 3D-scanning, avatar, recog- nition, psychophysics, perceptually adaptive graphics One of the primary goals of computer graphics is to produce realistic images. In this, computer graphics has so far largely relied on the physical modeling of object properties— examples range from the rendering equation [Kajiya 1986] based on radiative heat transfer to facial animation based on physical simulation of muscles and skin tissue [K¨ ohler et al. 2002]. Increasingly sophisticated algorithms together with an enormous increase in com- puting power have enabled researchers to produce amazing images of natural and artiﬁcial scenes. A question that has emerged in recent years is, however: “How do we know when to stop?”, or “When is realism ‘realistic enough’ ”? In this paper, we approach the question of realism from the viewpoint of human perception: What is needed in order to produce perceptually realistic images? By asking this question we have thus chosen the human ... Permission to make digital/hard copy of all or part of this material without fee for personal or classroom use provided that the copies are not made or distributed for proﬁt or commercial advantage, the ACM copyright/server notice, the title of the publication, and its date appear, and notice is given that copying is by permission of the ACM, Inc. To copy otherwise, to republish, to post on servers, or to redistribute to lists requires prior speciﬁc permission and/or a fee. c  20YY ACM 0000-0000/20YY/0000-0001 $5.00 ACM Transactions on Applied Perception, Vol. V, No. N, Month 20YY, Pages 1–22.