# Detection of Fungal Infections on the Wood Surface Using LTM Imaging
## 4 Discussion  
Both measurement methods--i.e., measurement of the infected area and profile analysis--use the phenomenon of scattering and absorption of the laser beam in the infected areas. Measuring the surface area with a resolution of 0.25 mm in the X and Y axes guarantees the verification of 16 measurement points in an area of 1 mm\({}^{2}\). It ensures an accurate check of the entire board surface. The use of profile analysis does not allow a detailed assessment of the presence of infection. However, it can only be used as an indicator in applications where it is impossible to build up a complete surface image of the board due to the technological line's design. The best results for detecting an infected surface were obtained at a power of 6-7 mW. Imaging can also be performed with laser power specified in the range of 8 to 9 mW. However, the differences in area measurement in the infected area and in the area without infection will be smaller. These differences will only be visible on heavily infected surfaces. Slightly infected areas will be counted as non-infected ones. During the tests, it was observed that the choice of laser power depends on the moisture content of the controlled boards. An additional 20-30% increase in humidity enhances the scattering and absorption of the laser beam, even on non-infected surfaces. The laser power selected when imaging was realized in such cases increased by about 2 mW. Depending on the chosen laser power, the recording time for a single height profile and the operating frequency of the vision system must also be selected. Tests were performed with frequencies ranging from 100-500 profiles per second. The research used a laser emitting electromagnetic radiation with a laser wavelength of 658 nm. The question arises whether the use of a laser emitting other wavelengths would have altered the scattering and absorption effect of the laser beam on the infected surfaces used. And if so, would an enhancement of this effect or weakening it be achieved? However, the choice of a different type of laser and the selection of its power should be confronted with the safety regulations applicable to production lines. These could be the subjects of further research carried out on this topic. Most solutions presented in the literature are based on advanced conventional algorithms or algorithms based on artificial intelligence. However, this requires advanced parameterization of the vision system or a significant increase in the computing power used  
Figure 13: View of the infected area in a 3D image captured with a laser operating power at 7 mW. for such tasks. Making changes to the operation of such algorithms involves modifying them or repeating the network learning procedure [4; 18; 19; 20]. Image acquisition is carried out while the board is being transported on a conveyor. It, therefore, does not require stopping the product for imaging. The image analysis carried out is based on a fast algorithm for surface area measurement. The time required for image analysis and display of the analysis result for the board sorting system is no more than 10 ms. In addition, the use of laser power control makes it possible to amplify the difference between infected and non-infected surfaces already at the image acquisition stage. Operators can quickly calibrate and tune the laser power for a new batch of products. A change in wood species or a change in wood moisture content allows efficient management of the product inspection system. The image construction using LTM enables the differences between the infected area and the area without infection to be effectively indicated. In addition, these differences are amplified already at the image acquisition stage. The evaluation of the board area can be further shortened by considering only a selected height profile for analysis.