  Recently, a successful pose estimation algorithm, called Cascade Pose
Regression (CPR), was proposed in the literature. Trained over Pose Index
Feature, CPR is a regressor ensemble that is similar to Boosting. In this paper
we show how CPR can be represented as a Neural Network. Specifically, we adopt
a Graph Transformer Network (GTN) representation and accordingly train CPR with
Back Propagation (BP) that permits globally tuning. In contrast, previous CPR
literature only took a layer wise training without any post fine tuning. We
empirically show that global training with BP outperforms layer-wise
(pre-)training. Our CPR-GTN adopts a Multi Layer Percetron as the regressor,
which utilized sparse connection to learn local image feature representation.
We tested the proposed CPR-GTN on 2D face pose estimation problem as in
previous CPR literature. Besides, we also investigated the possibility of
extending CPR-GTN to 3D pose estimation by doing experiments using 3D Computed
Tomography dataset for heart segmentation.
