G. Bebis et al. (Eds.): ISVC 2007, Part I, LNCS 4841, pp. 137–148, 2007. © Springer-Verlag Berlin Heidelberg 2007 Blur in Human Vision and Increased Visual Realism in Virtual Environments Michael S. Bittermann, I. Sevil Sariyildiz, and Özer Ciftcioglu Delft University of Technology Abstract. A challenge for virtual reality (VR) applications is to increase the re- alism of an observer’s visual experience. For this purpose the variation of the blur that an observer experiences in his/her vision, while he/she focuses on a particular location, can be mimicked by blurring the VR computer graphics based on a model of the blur. The blur in human vision is the result of a combi- nation of optical and neural vision processes; namely optical refraction, non- uniform retinal sampling, and cortical magnification. Due to the complexity of the phenomenon, apparently no theoretical model of the blur has been pub- lished. In this work we model the combined effect by means of a probabilistic model of the human visual system. The results from the models match common vision experience verifying the validity of the underlying theoretical considera- tions. The implementation of the model for increased realism in virtual reality is illustrated by means of a rendering of a virtual reality scene, which is processed for two different acts of focusing. 1 Introduction Traditional applications of virtual reality (VR) are medical surgery training, flight and driving simulation, as well as industrial and architectural design [1, 2]. In the applica- tions usually a high degree of visual realism is desired for increased effectiveness. Visual realism concerns both, the experienced egocentric and exocentric distances, and the level of visual detail of the environment. A source reducing visual realism of VR experience is the fact that a virtual scene is usually rendered on a 2-dimensional display, so that an observer has some awareness of the display surface [3]. There is evidence that awareness of the display surface interferes with the perceived three- dimensionality of a scene displayed [4, 5]. This evidence appears to corroborate with experiments where absolute egocentric distances are found to be generally underesti- mated in VR [6, 7], while a number of possible reasons for this can be ruled out [8, 9], including the quality of the computer graphics as claimed by [10]. The visual experience of an object differs from the experience of the object’s coun- terpart in VR. One difference is the experienced variation of visual detail on the ob- ject when we focus our vision to a certain location on it. This phenomenon we refer to as blur phenomenon. When we focus on a surface patch S 1 of an object, we experience the patch as visually sharp. When we keep focusing on S 1 , we experience another patch S 2 located at some distance from S 1 as less sharp, i.e. blur. The degree of ex- perienced blur depends on the geometric relation among S 1 , S 2 , and the location of