  In natural images, the scales (thickness) of object skeletons may
dramatically vary among objects and object parts, making object skeleton
detection a challenging problem. We present a new convolutional neural network
(CNN) architecture by introducing a novel hierarchical feature integration
mechanism, named Hi-Fi, to address the skeleton detection problem. The proposed
CNN-based approach has a powerful multi-scale feature integration ability that
intrinsically captures high-level semantics from deeper layers as well as
low-level details from shallower layers. % By hierarchically integrating
different CNN feature levels with bidirectional guidance, our approach (1)
enables mutual refinement across features of different levels, and (2)
possesses the strong ability to capture both rich object context and
high-resolution details. Experimental results show that our method
significantly outperforms the state-of-the-art methods in terms of effectively
fusing features from very different scales, as evidenced by a considerable
performance improvement on several benchmarks.
