Expression Robust 3D Facial Landmarking via Progressive Coarse-to-Fine Tuning

Abstract

Facial landmarking is a fundamental task in automatic machine-based face analysis. The majority of existing techniques for such a problem are based on 2D images; however, they suffer from illumination and pose variations that may largely degrade landmarking performance. The emergence of 3D data theoretically provides an alternative to overcome these weaknesses in the 2D domain. This article proposes a novel approach to 3D facial landmarking, which combines both the advantages of feature-based methods as well as model-based ones in a progressive three-stage coarse-to-fine manner (initial, intermediate, and fine stages). For the initial stage, a few fiducial landmarks (i.e., the nose tip and two inner eye corners) are robustly detected through curvature analysis, and these points are further exploited to initialize the subsequent stage. For the intermediate stage, a statistical model is learned in the feature space of three normal components of the facial point-cloud rather than the smooth original coordinates, namely Active Normal Model (ANM). For the fine stage, cascaded regression is employed to locally refine the landmarks according to their geometry attributes. The proposed approach can accurately localize dozens of fiducial points on each 3D face scan, greatly surpassing the feature-based ones, and it also improves the state of the art of the model-based ones in two aspects: sensitivity to initialization and deficiency in discrimination. The proposed method is evaluated on the BU-3DFE, Bosphorus, and BU-4DFE databases, and competitive results are achieved in comparison with counterparts in the literature, clearly demonstrating its effectiveness.