Loss function inversion for improved crack segmentation in steel bridges using a CNN framework

Automating bridge visual inspection using deep learning algorithms for crack detection in images is a prominent way to make these inspections more effective. This paper addresses several challenges associated with crack detection: (1) data imbalance, caused by a small crack area as compared to the background, and (2) a high false positive rate, due to a large amount of crack-like features in the background. First, a new benchmark dataset is presented, containing images of cracks in steel bridges along with pixel-wise annotations. Secondly, the importance of incorporating background patches is examined to assess their impact on network performance when applied to high resolution images of cracks in steel bridges. Finally, a loss function is introduced that enables the use of a relatively large number of background patches in neural network training. The proposed approaches yield a significant reduction in false positive rates, thereby improving the overall performance of crack segmentation. • An annotated dataset of images of fatigue cracks in steel bridges is published. • Crack segmentation performance improved by modification of a CNN architecture. • Increase of patch size significantly improves performances of segmentation of cracks. • Global image context is important for robust segmentation of cracks.