# Three-Dimensional Imaging of Metallic Grain by Stacking the Microscopic Images
## 4 Discussion  
In this study, a method and its implementation algorithm for the three-dimensional observation of the microstructure of carbon steel (SA106) was proposed while explaining and illustrating its principle.  
The visualization of the shape of the 3D grains with simple equipment, namely a polishing machine, a metallurgical microscope, and some algorithms, is a great advantage. Moreover, it is inexpensive and easy to implement due to its simple technique and does not involve extensive hardware and software.  
While the mounted object was being polished, a photograph of the layer was taken using a metallurgical microscope. Subsequently, the metallic MG was reconstructed in three dimensions by assembling and processing the collected 2D images through local positioning, MG selection, binarization, resizing, stacking (superimposing), and surfacing, which provides very accurate data. The assembly and processing techniques are based on mathematical formulae as described above; the program derived from these formulae is straightforward. It is easily accessible and provides a quick result, making it a simple resource to operate and can be implemented in general-purpose software, e.g., MATLAB, C, C++, Python.  
Figure 10: Three-dimensional volumetric imaging of grains with except discontinuous layers. (**a**) 3D image of #1; (**b**) 3D image of #3; (**c**) 3D image of #6; and (**d**) 3D image of three grains.  
As shown in the example in Figure 6, the MG image is designed by a large number of nodes and will require a lot of computational power. To overcome this, skipping is necessary. However, there is a limit, which should not be exceeded, to not compromise the accuracy of the final results. Skipping by nine, in this case, leads to both minimal resources simulation time and accurately obtained results. Organizational photos may contain personal opinions. In other words, the shredded pieces may, in fact, be the tip of a large layer. If this personal subjectivity is expressed in three dimensions, a somewhat objective judgment is possible.  
Notwithstanding non-destructive testing techniques, three-dimensional imaging grains will be one of the most widely used techniques in the near future. Firstly, for its numerous advantages listed in the introduction. Another interest is to be able to reconstruct the shape of the microstructure, which may allow the evaluation and prediction of the material's behavior under stress, damage, heat treatment effects, etc., and a variety of research has been carried out in this area [19; 44; 45].  
The reconstructed 3D grains volume, as illustrated in Figure 10, from the processed 2D images is of significant interest and may be useful for our future research in the field of non-destructive evaluation using mainly electromagnetic and ultrasonic testing to better understand structural properties at the microstructural level. In addition, the generation of a three-dimensional grains structure may also broaden the scope of applications, especially in the field of materials science, designing structural materials, and investigation of engineering materials.  
In the last few years, thanks to numerical models and the increase in computing and processing capacity, it has become possible to obtain precise models and simulations of complex material properties, especially microstructures, using advanced software and modeling techniques [46; 47; 48]. The software algorithms developed under MATLAB employed are complementary to the experimental work, and the combination of the two leads to more accurate and realistic grain representations with a very acceptable simulation time. In addition, the method allows the creation of microstructures with the exact shape and size of the grains and offers the possibility of selecting one or more grains, as illustrated in Figures 7, 8 and 10.