Analysis of Fine Crack Images Using Image Processing Technique and High-Resolution Camera

Abstract

Visual inspections are performed to investigate cracks in concrete infrastructure. These activities require manpower or equipment such as articulated ladders. Additionally, there are health and safety issues because some structures have low accessibility. To deal with these problems, crack measurement with digital images and digital image processing (DIP) techniques have been adopted in various studies. The objective of this experimental study is to evaluate the optical limit of digital camera lenses as working distance increases. Three different lenses and two digital cameras were used to capture images of lines ranging from 0.1 to 0.5 mm in thickness. As a result of the experiments, it was found that many elements affect width measurement. However, crack width measurement is dependent on the measured pixel values. To accurately measure width, the measured pixel values must be in decimal units, but that is theoretically impossible. According to the results, in the case of 0.3 mm wide or wider cracks, a working distance of 1 m was secured when the focal length was 50 mm, and working distances of 3 m and 4 m were secured when the focal length was 100 mm and 135 mm, respectively. However, for cracks not wider than 0.1 mm, focal lengths of 100 mm and 135 mm showed measurability within 1 m, but a focal length of 50 mm was judged to hardly enable measurement except for certain working positions. Field measurement tests were conducted to verify measurement parameters identified by the results of the indoor experiment. The widths of actual cracks were measured through visual inspection and used for the analysis. From the evaluation, it was confirmed that the number of pixels corresponding to the working distance had a great influence on crack width measurement accuracy when using image processing. Therefore, the optimal distance and measurement guidelines required for the measurement of the size of certain objects was presented for the imaging equipment and optical equipment applied in this study.

Non-Destructive Testing in Civil Engineering

“…In turn, article [2] is devoted to the identification of cracks in concrete. The work associated with this kind of research requires effort and equipment, such as articulated ladders.…”

Deep Learning for Concrete Crack Detection and Measurement

“…Although many studies have successfully measured concrete crack width by using pixels, this unit of measurement remains a significant limitation: this is because determining the width of concrete cracks in pixels does not provide practical information for field applications, as the severity of concrete crack width is better understood in millimetres. Some studies [36][37][38][39][40][41] have found ways to measure concrete crack width in millimetres by devising methods to carry out pixel to millimetre conversion. However, Nyathi et al [5] found that these methods require knowledge of key parameters that may not always be readily available, such as focal length, camera resolution, number of pixels along the long side of image sensor, etc.…”

Concrete Crack Width Measurement Using a Laser Beam and Image Processing Algorithms

“…Jeong et al [29] used Otsu image processing to measure crack width in pixels. The crack width was converted to millimeters using a proposed equation shown in Equation (3).…”