Stereoscopic video telephony: naturalness and sense of presence

Previous research from our laboratory indicated that sense of presence is enhanced for stereoscopic images with scenes typical of video telephone (VT) systems, compared to non-stereoscopic 2-D images. However, this enhancement was not found for all sequences. In the present study we report results obtained with a new set of stereoscopic sequences containing depth scenes that were created through manipulation of camera focal length, background scene, and camera convergence point. Viewers were asked to rate both stereoscopic and non-stereoscopic versions of the sequences on naturalness and sense of presence. The methodology of double-stimulus, continuous quality scale (ITU-R Recommendation 500) was used in the subjective assessment. Images in the video sequences were common image format (CIF, 352 x 240 pixels) with a display size of 15.5 cm x 11.6 cm. The results confirmed our previous findings that sense of presence is enhanced for certain stereoscopic video sequences, compared to non-stereoscopic sequences. The results also indicate a high correlation between ratings of naturalness and sense of presence (r2 = 0.75), although ratings tended to be lower for naturalness than for presence. Both ratings tended to improve slightly with camera focal length, except for sequences with a natural background. For the range studied, no effect of camera convergence point was found.