“…Indirect methods rely on the results of Digital Image and Volume Correlation techniques (DIC/DVC), as shown in Figure 1b. Direct methods typically involve a preprocessing step [1,4,5], such as smoothing, filtering, or contrast enhancement, followed by a detection step, which may use morphological, statistical [6,7] (e.g., Gabor filter bank (GFB), Grey Level Co-occurrence Matrix (GLCM), Local Binary Matrix Feature Extraction (LBFE)), or machine learning methods [1,8,9]. Pixel-intensity-based crack detectors depend on the lighting conditions and require a homogeneous appearance of the uncracked areas [10]; indeed one of the main limitations of the image-based techniques is that the surface noise might be considered a crack [11].…”