Stereoscopic displays afford more accurate 3D percepts than conventional displays due to the added depth cue of disparity. However, 3D shape and scene layout are often misperceived when viewing stereoscopic displays. For example, viewing from the wrong distance alters an object's perceived size and shape. It is crucial to understand the causes of such misperceptions so one can determine the best approaches for minimizing them. We develop the mathematics of an existing geometric model for calculating misperceptions, and then describe common viewing situations in which the model fails to make a prediction. We show how the visual system's interpretation of vertical disparities can supplement the existing model and help predict the percepts associated with improper viewing of stereoscopic displays.
We also discuss blur as a previously under-appreciated depth cue present in both stereo and non-stereo images. We present a probabilistic model that explains how the pattern of blur in an image together with relative depth cues indicates the apparent scale of the image's contents. To examine the correspondence between the model/algorithm and actual viewer experience, we conducted an experiment with human viewers and compared their estimates of absolute distance to the model's predictions. We did this for images with geometrically correct blur due to defocus and for images with commonly used approximations to the correct blur. The agreement between the experimental data and model predictions was excellent. A semi-automated algorithm is included, which helps one apply the correct pattern of blur to change the apparent size of a scene. The algorithm and model allow one to manipulate blur precisely and to achieve the desired perceived scale efficiently.
Finally, we discuss the utility of stereoscopic displays for medical imaging. The technology's greatest benefits arise in applications in which monocular cues are uninformative. Its specific strengths and shortcomings are presented in terms of diagnostics, education, surgical planning, minimally invasive surgery, and telesurgery. General guidelines and common errors are also listed to help potential users avoid unwanted misperceptions and visual fatigue.