Binocular depth perception of stereoscopic 3D line drawings

Stereoscopic 3D exploits the effects of stereopsis where the depth perception is triggered by binocular disparity, a difference in image location of an object by the left and right eyes. Despite the dissimilarity of stereo projections in terms of disparity and shape, the human visual system can find the matching stereo pair to fuse using their similarities in terms of color, size, shading, texture, shadows, that are normally present in photorealistic stereo imaging. Now if some of these elements (or depth cues) are missing, such as in non-photorealistic stereo imaging, how will it affect the depth perception and stereo fusion? In this paper, we investigate this issue by conducting a perceptual study on stereoscopic 3D line drawing, in which many of these cues have been abstracted away. We first evaluate the validity of using stereo images composed of lines only, and then compare its performance to stereo images of normal shading. We also examine the effect of changing line style as well as the prospect of using lines as an additional depth cue. Our study shows that stereo line drawing, when compared to stereo shading, does weaken the depth perception but only to a minor degree. On the other hand, modification of line style, and superimposition of stereo lines both have potentials to strengthen the perception of depth.