[Philip Lelyveld comment: this article contains many useful graphs]
My company’s main interests are stereo correction, stereo conversion to multiview and 2D-to-stereo 3D conversion using depth maps. From a practical perspective, the following initial questions arise when developing algorithms and software for 3D video conversion and quality improvement:
• How significant is the difference in stereo perception among different people? What does the stereo perception ‘distribution’ function look like?
• Which characteristics of a stereo image are important for subjective perceived quality?
• In which cases are stereo artefacts (due to imperfect 2D-to-3D conversion, stereo mismatch or a distorted depth or disparity map) noticeable, and when are they not so noticeable? When are perfectly-detailed depth maps important, and when are they superfluous?
A number of tests were conducted to find partial answers to these questions, and the work is still ongoing. The following issues were studied first:
• Stereo sensitivity, ability to perceive 3D.
• Subjective stereo acuteness.
On the basis of these stereo sensitivity and acuteness tests, several conclusions can be drawn and common-knowledge opinions confirmed:
• Variance in subjective stereo perception is very large. Up to 30% of test participants are barely susceptible to stereo for, apparently, various reasons – even in the case of close-to-normal 2D vision. Weak 2D vision is not the only cause of bad stereo vision, although it does have an influence. Thus, the question arises, to what extent is it conditioned by the particulars of artificial digital stereo, and to what degree is it due to the individual properties of eyes and the brain’s sensory system?
The second question relates to whether there is a strong relationship between stereo sensitivity and comfort when viewing the same stereo video. If such a relationship exists, how should 3D video be prepared for people with different stereo perception characteristics?
• Subjective stereo perception is adaptive. This conclusion does not relate only to the latency of proper eye convergence; some brain learning is involved. After training, people notice more 3D details under the same conditions. This result is related to the assertion that drastic depth changes over time should be avoided in stereo video, as they ‘defocus’ stereo vision.
• For depth map construction and stereo generation, an important conclusion is that roughness and deviations in depth that are irrelevant to the underlying 2D image are noticeable as unpleasant artefacts only in highly-detailed areas with sharp edges. So, the masking effect of rough surfaces in 2D images, when artefacts in detailed areas are often imperceptible, works in the opposite way with stereo. Likely, very irregular textures are still less revealing because the brain must match numerous random-looking features that are hard to discern.
• 2D-to-3D conversion and stereo correction artefacts in flat uniform areas are invisible to nearly all viewers; only the borders of such areas should be accurately processed.
If you have a 3D display or a pair of red/cyan glasses (red for left eye, cyan for right) you can check your stereo vision using the methods described in this article by watching the following video: …