Pyramid ALKNet for Semantic Parsing of Building Facade Image

The semantic parsing of building facade images is a fundamental yet challenging task in urban scene understanding. Existing works sought to tackle this task by using facade grammars or convolutional neural networks (CNNs). The former can hardly generate parsing results coherent with real images while the latter often fails to capture relationships among facade elements. In this letter, we propose a pyramid atrous large kernel (ALK) network (ALKNet) for the semantic segmentation of facade images. The pyramid ALKNet captures long-range dependencies among building elements by using ALK modules in multiscale feature maps. It makes full use of the regular structures of facades to aggregate useful nonlocal context information and thereby is capable of dealing with challenging image regions caused by occlusions, ambiguities, and so on. Experiments on both rectified and unrectified facade data sets show that ALKNet has better performances than those of state-of-the-art methods.