- 1 - A Method of Computational Correction for Optical Distortion in Head-Mounted Displays Jannick P. Rolland and Terry Hopkins Dept. of Computer Science, University of North Carolina, Chapel Hill, NC 27599-3175, U.S.A. Abstract Optical distortion is one of the optical aberrations of optical systems that do not affect image sharpness. Thus, it can be beneficial to correct optical distortion computationally rather than optically. Computational correction versus optical correction will generally yields lighter optical systems. This is of great importance for head-mounted displays where the weight of the viewer needs to be minimized for efficient performance, safety, and optimum duration of usage. We shall describe in this paper, one method of computational correction that consists in warping polygon vertices. It is the case, however, that the algorithms given can be easily rewritten to handle pixels rather than vertices warpings. 1. Introduction A head-mounted display (HMD), head tracker, computer graphics system, and appropriate display software may be used to give a user the perception of a computer-generated space which is spatially stable. Different names, such as virtual reality, cyberspace, artificial reality, virtual environments, and synthetic experience, have been used to describe the perception produced by this apparatus. In order to generate a pair of stereoscopic images for the two display devices in the HMD, the display software must take into account the relative positions of the head tracker, the display devices, the optics, and the user’s eyes (Robinett and Rolland, 1992). To simulate objects that are spatially stable and shape invariant regardless of their position in the world, both spatial and temporal problems must be solved. This paper focuses on the optical imaging or static image generation problem. Temporal problems will be treated elsewhere (Adelstein et al. 1992 and work in progress at the University of North Carolina at Chapel Hill (UNC-CH)). The purpose of the optics used in an HMD is to project equally magnified images to the eyes of the user in such a way that they fill or partially fill the user’s field of view. Moreover, the optics also (and in some cases, only) serves as an auxiliary to the lens of the eye so that the latter remains at rest (i.e., at infinity focus). In any case, the focal length of the optics as well as the distance of the miniature displays to the optics must be chosen such that the so-formed virtual images fall within the range of accommodation (focus) of the eyes. When the eyes accommodate on the virtual images, the virtual environment can be seen in focus and its image sharpness is only limited by the resolution of the displays. There is evidence in the literature, however, that what sets accommodation in HMDs is not so simple and that the predictions which come from optical image formation can be violated. A review of the problem of accommodation in HMDs can be found in (Rolland et al., 1993).