Fig. 1. Acquisition of the ROI image. (a) Mask process schematic; (b) original image; (c) mask image; (d) ROI image

Fig. 2. Flow chart of double threshold algorithm

Fig. 3. Bilateral filtering image after increase the dimension

Fig. 4. Tensor voting. (a) Ball voting field; (b) stick voting field; (c) schematic of tensor voting rules; (d) probability significance map

Fig. 5. Complete crack acquisition process

Fig. 6. (a) Experimental equipment; (b) image of components

Fig. 7. Performance evaluation of algorithm. (a) Different threshold; (b) different σ values; (c) runtime

Fig. 8. Image processing and results with double threshold. (a) ROI images; (b) images obtained by Otsu algorithm; (c) images obtained by the double threshold

Fig. 9. Crack detection on five images. (a) Original images; (b) detection results by crack connection algorithm; (c) cracks detection results by proposed algorithm; (d) truth cracks