Stereopsis is a visual process in which a viewer perceives depth in an image of a scene by presenting the viewer's left-eye viewpoint with a first projection of the scene and presenting the viewer's right-eye viewpoint with a second but different projection of the same scene. Stereopsis is processed in the visual cortex in binocular cells having receptive fields in different horizontal positions in the viewer's two eyes. Binocular cells are active only when its preferred stimulus is in the correct position in the left eye and in the correct position in the right eye, making the binocular cells disparity detectors. When a viewer stares at a main object, the viewer's two eyes converge so that the object appears at the center of the retina in both eyes. Other objects around the main object appear shifted in relation to the main object. Because each eye is in a different horizontal position, each eye has a slightly different perspective on a scene yielding different retinal images. When the relative orientations of these two projections are correct, the viewer's brain ideally interprets the visual differences between the images as a single undistorted three-dimensional image.
In recent years, the advent of stereo display technologies enabling viewers to perform stereopsis with two-dimensional displays has been gaining interest and acceptance. With typical stereo display technology, viewers are required to wear eye glasses that control the visual content delivered to each eye. However, it is typically the case that the relative orientations of the projections received by the viewer are correct only for certain viewing locations, such as locations where a viewer's view is orthogonal to the center of a display. By contrast, viewers watching the same display outside these viewing locations experience a re-projection error that manifests as a vertical misalignment of the visual content received by the eyes of the viewers. If the images are very different, then in some cases one image at a time may be seen, a phenomenon known as binocular rivalry. Another type of visual artifact in typical stereo display technologies is that foreground and background objects often appear with the same focus. In order to produce a realistic three-dimensional viewing experience close objects should appear out of focus when the viewer focuses on more distant objects in the same image, and vice versa. These kinds of visual artifacts can be distracting and are cumulative to most viewers, leading to eye strain, nausea, fatigue, and possibly rejection of the stereo display technology. Thus, mere below threshold objectionableness may not be sufficient for permitting the presence of such artifacts.
Designers and manufacturers of stereo display systems continue to seek improvements that reduce the adverse effects associated with typical stereo display technology.