3D face reconstructions from photometric stereo using near infrared and visible light

This paper seeks to advance the state-of-the-art in 3D face capture and processing via novel Photometric Stereo (PS) hardware and algorithms. The first contribution is a new high-speed 3D data capture system, which is capable of acquiring four raw images in approximately 20 ms. The results presented in this paper demonstrate the feasibility of deploying the device in commercial settings. We show how the device can operate with either visible light or near infrared (NIR) light. The NIR light sources offer the advantages of being less intrusive and more covert than most existing face recognition methods allow. Furthermore, our experiments show that the accuracy of the reconstructions is also better using NIR light. The paper also presents a modified four-source PS algorithm which enhances the surface normal estimates by assigning a likelihood measure for each pixel being in a shadowed region. This likelihood measure is determined by the discrepancies between measured pixel brightnesses and expected values. Where the likelihood of shadow is high, then one light source is omitted from the computation for that pixel, otherwise a weighted combination of pixels is used to determine the surface normal. This means that the precise shadow boundary is not required by our method. The results section of the paper provides a detailed analysis of the methods presented and a comparison to ground truth. We also analyse the reflectance properties of a small number of skin samples to test the validity of the Lambertian model and point towards potential improvements to our method using the Oren–Nayar model.