SRNet: Structural Relation-aware Network for Head Pose Estimation

Estimating head pose from a single RGB image has recently attracted considerable research attention. Prior arts employ a CNN backbone to process face images and then directly output Euler angles. We argue that they may ignore essential features that are highly correlated to head pose due to the non-global perspective, and the ambiguity and discontinuity issues of Euler angles representation could interfere with the performance of challenging samples. In this paper, we formulate the head pose estimation problem into quaternion representation space and propose a novel framework named Structural Relation-aware Network (SRNet). Different from previous methods, our SRNet explicitly explores the correlation among different regions of the face for mining global facial structure information. Furthermore, in order to boost robustness and generalization of the model, a hard example mining (HEM) strategy is designed to mitigate the data imbalance issue by adjusting the contributions of examples in different states to loss. Extensive experiments demonstrate that our method outperforms the current state-of-the-art alternatives on the public benchmark datasets: AFLW2000 and BIWI.