Zig-Zag Network for Semantic Segmentation of RGB-D Images

Semantic segmentation of images requires an understanding of appearances of objects and their spatial relationships in scenes. The fully convolutional network (FCN) has been successfully applied to recognize objects' appearances, which are represented with RGB channels. Images augmented with depth channels provide more understanding of the geometric information of the scene in an image. In this paper, we present a multiple-branch neural network to utilize depth information to assist in the semantic segmentation of images. Our approach splits the image into layers according to the "scene-scale". We introduce the context-aware receptive field (CARF), which provides better control of the relevant context information of learned features. Each branch of the network is equipped with CARF to adaptively aggregate the context information of image regions, leading to a more focused domain that is easier to learn. Furthermore, we propose a new zig-zag architecture to exchange information between the feature maps at different levels, augmented by the CARFs of the backbone network and decoder network. With the flexible information propagation allowed by our zig-zag network, we enrich the context information of feature maps for the segmentation. We show that the zig-zag network achieves state-of-the-art performances on several public datasets.