# Detection of Fungal Infections on the Wood Surface Using LTM Imaging
## 2 Methods of Surface Imaging  
This paper presents the subject of the identification of defects associated with the presence of various surface infections observed as fungi. For this, a 3D image was made using the LTM with control of the laser illuminator power. As part of the preparatory work, tests were carried out on material in the form of boards supplied by sawmills. Some of the boards delivered from sawmills were found to be infected with various fungal species. Fungal infections on the surface of boards originate and develop both at the stage of wood storage in the forest and processing in sawmills. Defects may also develop during the transport of boards from the sawmill to the factory. Studies to identify the type of fungi that develop most frequently on the surface of boards have found the presence of blue-rot fungi, rot fungi and mold fungi [31; 32; 33]. Both 2D and 3D imaging methods were considered in the process of selecting the imaging method. Due to the need to image different species of wood (pine and spruce) and the need to image a product in motion, moved-on conveyors, an imaging method based on the use of LTM and the construction of a 3D image of the product was selected. Figure 1: Examples of fungal infections: the fungus _Ceratocysts pinicola_ visible on the surface of boards delivered from the sawmill. Recording an image using the LTM involves determining the height profiles of the object and combining these profiles in a 3D image. Imaging is carried out using a RangerE area scan camera and laser line illuminator (Figure 2a). The camera is positioned at an angle to the laser beam. It captures an image of the laser line visible on the surface of the object (Figure 2a,b). A height profile is then determined based on the geometric relationships resulting from the camera's geometry and laser setup. Based on the analysis of the beam image and knowledge of the camera's parameters and laser alignment geometry concerning the object, the height profile in a cross-section perpendicular to the surface is determined (Figure 2c). By determining a set of height profiles for successive positions of the object moved with respect to the laser-camera system along the Y-axis, a description of the surface of the object under study is realized (Figure 2a). A three-dimensional image of the object surface is built by accumulating profiles in a matrix in its successive rows. The number of measurement points forming a single height profile corresponds to the number of columns on the sensor. The number of profiles determined for an object corresponds to the number of rows in the matrix. For 3D vision systems using the LTM, the coordinate system is adopted in such a way that the X-axis is parallel to the laser plane. The Y axis is adopted according to the object's direction of movement during the determination of successive height profiles. The resolution of a 3D vision system is the minimal visible change in the measurement that can be recorded in a 3D image. For imaging with 3D vision systems, the resolution is determined in the direction of the three axes of the coordinate system associated with the measurement and control station. The following designations are used in this paper:  
\(\Delta X\)--resolution in the X-axis direction, i.e., along the laser line,  
\(\Delta Y\)--resolution towards the Y axis, i.e., the axis perpendicular to the laser line and, at the same time, the direction of movement of the object under examination,  
\(\Delta Z\)--resolution in the Z-axis direction of the vision system coordinate system. When calculating the imaging resolution in the configuration shown in Figure 2b, an approximation is used in which we assume that the angle \(\alpha\) is equal to the angle \(\alpha_{1}\). In reality, the angle \(\alpha_{1}=\alpha-\gamma\). 3D vision systems use resolutions of \(\Delta X=0.1\) mm or greater. Figure 2: 3D surface image acquisition: (**a**) vision station model, (**b**) vision system geometry configuration, (**c**) height profile and the 3D surface of the board.