U2CrackNet: a deeper architecture with two-level nested U-structure for pavement crack detection

Crack detection is important for evaluating pavement conditions. In this paper, we propose an automatic pavement crack detection method called as U2CrackNet. The architecture of U2CrackNet is a two-level nested U-structure which is an encoding and decoding architecture. Firstly, the crack features are extracted by the encoding layer so that the preliminary effective feature layer is obtained. Subsequently, the encoder and decoder are connected by an atrous spatial pyramid pooling (ASPP) model. The atrous convolution with different expansion rates can be used to capture the multi-scale crack information. Besides, in order to make the network pay more attention to the features of cracks, the crack feature map channels are given different weights through the effective channel attention mechanism after upsampling in the decoding layer. Finally, the crack saliency probability maps generated by each layer of the network are fused into the final crack saliency map through cascade operation. The proposed method has been evaluated on an expanded pavement crack dataset containing 8700 images. The experimental results demonstrate that the proposed U2CrackNet can obtain more clear and continuous cracks. Specifically, the precision, accuracy, F1-score, and Mean Intersection over Union (MIoU) are 89.51%, 98.95%, 81.45%, and 69.19%, respectively.