# Detection of Fungal Infections on the Wood Surface Using LTM Imaging
## 2 Methods of Surface Imaging
Consequently, this simplification does not significantly affect the value of the determined resolution. The imaging resolution in the Z-axis is determined from the relationship:  
\[\Delta Z=\frac{\Delta X}{\sin\alpha} \tag{1}\]  
\(\alpha\)--the angle between the optical axis of the camera and the optical axis of the laser. The 3D imaging resolution of the plank surface was calculated considering the dimensions of the board subjected to surface inspection (Figure 3). These dimensions were assumed to be 1200 \(\times\) 145 \(\times\) 22. The imaging field of view (FOV) was selected to be larger than the test object for such a defined test object. Resolution calculations for each X, Y and Z axis of the measurement system were made for the 1536 \(\times\) 512 sensor from the RangerE camera. The 3D image contains 1000 profiles in the Y direction. The following parameters were assumed for the calculations:  
\(\alpha\) = 30\({}^{\circ}\) to 70\({}^{\circ}\),  
FOV = 160 mm X-axis imaging field expressed in mm (boards = 140-160 mm),  
RM = 1400 pixel X-axis imaging field expressed in pixels (usable resolution of the sensor). \[\Delta X\ =\ 160\ \mathrm{mm}/1400\ \mathrm{pix}\ =\ 0.11\ [\mathrm{mm}/ \mathrm{pixel}] \tag{2}\]  
\[\Delta Y\ =\ 1200\ \mathrm{mm}/1000\ \mathrm{profile}\ =\ 1.2\ [\mathrm{mm}/ \mathrm{profile}] \tag{3}\]  
\[\Delta Z\ =\ 0.11\ [\mathrm{mm}/\mathrm{pix}]/\sin\ (45^{\circ})\ =\ 0.15\ [ \mathrm{mm}/\mathrm{pixel}] \tag{4}\]  
The geometry of the vision system and the choice of camera mounting angle and laserial illumination were selected based on an analysis of the possible installation conditions of the triangulation measurement system on the production line. It was assumed that the angle \(\alpha\) could be set between 30\({}^{\circ}\) to 70\({}^{\circ}\) (Figure 4). For such a selected range, the characteristics of the variation of resolution in the Z-axis as a function of \(\alpha\) angle were determined. Figure 4: 3D imaging resolution in Z-axes as a function of \(\alpha\) angle. Figure 3: 3D imaging resolution described on the object. For an angle of 30\({}^{\circ}\), the imaging resolution for a FOV = 160 mm is 0.25 mm/pixel, and for an angle of 70\({}^{\circ}\), it reaches 0.1 mm/pixel. Imaging with this resolution allows from 16 to 100 measurement points to be captured over an area of 1 mm\({}^{2}\). For the task of detecting infection, this resolution is surplus to requirements. Infected regions have significantly larger surface areas. The use of resolution at the designated level allows the additional task of assessing the quality of the geometric structure parameters of the board surface and its dimensions. The focus of this paper is on the selection of image acquisition parameters that enable the effective identification of infected areas. As a result of the analysis carried out on the imaging resolution, a resolution of 0.25 mm in the X and Y axes was used as a sufficient parameter. This means using 16 measurement points to describe an area of 1 mm\({}^{2}\). The reduction in the number of points describing the surface was also intended to reduce the analysis time of the entire image of the board surface. The reduction in time was required due to the need to inspect successive boards fed into the production line. Preliminary imaging was carried out using the comparison method. Two board surfaces were imaged simultaneously, a board without infection and a board infected with blue stain fungi (Figure 5). A 658 nm laser with a power of 20 mW was used in the study. Imaging with an assumed resolution of 0.25 mm in the X and Y axes and using a 20-mW laser allowed the construction of images of both surfaces (Figure 6), even though one of them is significantly infected. The 3D image of the surface was constructed at a frequency of 500 profiles per second. Using a laser of sufficiently high power (e.g., 20 mW), allows the acquisition of a three-dimensional image of the surface regardless of the presence of infection. The laser beam is visible on the boards.