## 1 Introduction  
In industrial sites, when defects occur during the manufacturing process or operation, inspection is performed using the non-destructive testing (NDT) techniques [1]. There are various types of the NDT techniques [2; 3; 4]; representative examples include visual testing (VT), acoustic emission (AE), penetrant testing (PT), magnetic particle testing (MPT), infrared thermography (IRT), ultrasonic testing (UT), radiographic testing (RT), and acoustic emission (AE). In the recent era of 4.0 NDT, the aforementioned technologies are essential elements of artificial intelligence (AI), and they determine the presence or absence of abnormalities in the inspection object in real time. Each technology can be appropriately selected depending on the inspection environment, shape of the object, inspection conditions, and cost. The characteristics of each NDT technology are as follows: VT technology is suitable for the monitoring and surface inspection of inspection targets in the production process. However, it is only capable of detecting surface defects and is highly dependent on the experience of the inspector. PT technology is suitable for the surface inspection of mass-produced products. However, it is limited to surface defects and is subject to many environmental variables. MPT technology can detect surface defects of ferromagnetic targets. However, it is limited to the surface and is only applicable to ferromagnetic materials. In addition, the surface of the inspection target must be flat and coatings must be removed. UT technology can inspect the surface or interior. However, it is mostly performed manually and relies on the skill and experience of the inspector, and the equipment is expensive. RT technology can inspect the surface or interior. However, it is expensive and time-consuming. In addition, it is hazardous to the body and causes waste problems due to radiation. AE technology allows for surface and internal defect inspection using information on abnormal propagation. However, the structure under inspection attenuates the stress waves. Table 1 shows the comparison for each NDT technology. Among the NDTs, active IRT is a technique that efficiently inspects a wide area in real time using a non-contact technique [8; 9; 10]. It is a highly reliable technology and has been widely applied in recent years. The IRT combines the advantages of various technologies. Active IRT has various types of heat sources, and the eddy current is popular among them. It is called eddy current thermography (ECT) or inductive thermography (IT) [11]. As the name of the technology suggests, it utilizes an eddy current as a heat source. An eddy current is induced in the inspection target by a coil through which an alternating current flows and the temperature of the surface of the heated inspection target is measured by the infrared (IR) camera. Considering the specimens of this study for the NDT technology presented in Table 1, it can be determined that, among IRT technologies, IT technology is suitable. IT technology can be classified into stationary and motional. Stationary IT technology has fixed inspection objects and IR cameras, while motional IT technology involves relative movement. Stationary IT technology is not suitable for wide-range inspection due to its limited measurement range. On the other hand, high-frequency IR cameras can inspect moving or rotating objects and have a very wide inspection range. However, various post-processing techniques are essential for the automatic defect detection of moving inspection objects. In general, the surface of the inspection object in industrial sites is often covered with foreign substances and is not smooth. In addition, emissivity adjustment is required for accurate temperature measurement of the IR camera, but it is impossible to attach black tape or paint all surfaces. When measuring a surface with non-uniform emissivity, the accuracy of defect detection based on deep learning may decrease.