[8] [8] Su T C, Yang M D. Application of morphological segmentation to leaking defect detection in sewer pipelines[J]. Sensors, 2014, 14(5): 8686–8704.

[9] [9] Vriesman D, Britto A S, Zimmer A, et al. Automatic visual in-spection of thermoelectric metal pipes[J]. Signal, Image and Video Processing, 2019, 13(5): 975–983.

[10] [10] Yang Z Y, Lu S H,Wu T, et al. Detection of morphology defects in pipeline based on 3D active stereo omnidirectional vision sensor[J]. IET Image Processing, 2018, 12(4): 588–595.

[13] [13] Haertel M E M, da Costa Pinto T L F, Júnior A A G. Trinocular stereo system with object space oriented correlation for inner pipe inspection[J]. Measurement, 2015, 73: 162–170.

[14] [14] Land E H, McCann J J. Lightness and retinex theory[J]. Journal of the Optical Society of America, 1971, 61(1): 1–11.

[15] [15] Bradley D, Roth G. Adaptive thresholding using the integral image[J]. Journal of Graphics Tools, 2007, 12(2): 13–21.