Is a no-reference necessary and sufficient metric for video frame and stereo view interpolation possible?

This paper explores a novel metric which can check the consistency and correctness of a disparity map, and hence validate an interpolated view (or video frame for motion compensated frame interpolation) from the estimated correspondences between two or more input views. The proposed reprojection error metric (REM) is shown to be sufficient for the regions where the observed 3D scene has no occlusions. The metric is completely automatic requiring no human input. We also explain how the metric can be extended to be useful for 3D scenes (or videos) with occlusions. However, the proposed metric does not satisfy necessary conditions. We discuss the issues which arise during the design of a necessary metric, and argue that necessary metrics which work in finite time cannot be designed for checking the validity of a method which performs disparity estimation.