Human Subject Distance Estimation Using the Pupillary Distance and Head Orientation

In this article we propose a method to estimate the distance to the camera of a human subject from a monocular image without restricting the orientation of the head. The inter pupillary distance of the subject is used as anchor to estimate the size of pixels in the plane of the subject and the distance to the camera is recovered from this measurement. The inter pupillary distance in the image is estimated by using a learning-based approach that detects the head of the subject and estimates the orientation of the head with respect to the optical axis of the camera. It also proposes a method to estimate the pupillary distance from 2 images. The proposed approaches are validated by comparing the recovered distance to the real distance obtained with an OptiTrack motion-capture system. It is demonstrated that using the proposed algorithm allows a more robust estimation of the distance regardless of the head rotation.