## 3 Results and Discussion
### Discrimination of Different Human Skin Tissues Using Vectorial Retardance
#### 3.2.2 Qualitative Assessment by True-Color Vectorial Retardance Imaging
Compared with Figure 6d,e, the vectorial retardance (Figure 6f) can enhance fiber contrast and clarity by visualizing more fiber details using true-color vectorial retardance imaging technology. In this approach as shown in Figure 6f, different brightness is modulated by the scalar retardance (Figure 6d), and the colors correspond to various orientations of fibers, which is almost consistent with the Figure 6e due to the small magnitude of \(R_{C}\) as shown in Figure 6c. By comparing the area marked by red arrows, Figure 6f shows the striped fibrils different from the surrounding colors, indicating they have different  
Figure 5: Imaging results of normal skin tissues: (**a**) microscopic intensity image of H&E stained section; (**b**) microscopic intensity image of unstained section; (**c**) horizontal retardance; (**d**) 45\({}^{\circ}\)-linear retardance; (**e**) circle retardance; (**f**) scalar retardance; (**g**) orientation of linear retardance; (**h**) vectorial retardance. The scale bar represents 50 \(\upmu\)m.  
orientations, which is close to that indicated in Figure 6e. In addition, we can hardly visualize a brightness gradient with the same color in the striped fibrils, representing that the fibrils content is similar, which is almost consistent with Figure 6d and cannot be shown in Figure 6e. In Figure 6f, the region pointed out by the red arrow can observe not only the neatly arranged bundled fibers but also the microfibrous structures. It highlights clear and specific orientations of the fibrils, which are the main compositions of the bundled fibers [34]. Typically, the collagen fibers are 1-8 \(um\) in diameter, while the fibrils are about 100 \(nm\)[61]. This demonstrates that the true-color vectorial retardance can highlight more fiber microstructures than the traditional retardance-related parameters. It is resulting from the brightness and color being determined by scalar retardance and orientation of the fast axis, making it possible to present fiber distribution and orientation information simultaneously in one image. To analyze the performance in identifying different human skin lesions by true-color vectorial retardance, Figure 7 shows the imaging results of BE and MM. Although the three retardance components (Figure 7(a1-c1) and Figure 7(a2-c2)) could demonstrate the specific details of fibers along different orientations, the information is complicated. Conventional microscopic intensity images of stained sections (Figure 7(d1,d2)) indicate varying degrees of degradation of fibers due to the presence of nevus cells and tumor cell nests in BE and MM tissues. However, fiber details are difficult to observe. The scalar retardance images ((Figure 7(e1,e2)) visualize the rough distribution of fibers, such as the regions pointed by the red arrows. Compared with the scalar retardance images, the true-color vectorial retardance images (Figure 7(f1,f2)) can highlight the different orientations of fibers in different colors, as pointed out by the red arrows. Figure 6: Results of normal skin tissues: (**a**) horizontal retardance; (**b**) 45\({}^{\circ}\)-linear retardance; (**c**) circle retardance; (**d**) scalar retardance; (**e**) orientation of linear retardance; (**f**) vectorial retardance. The scale bar represents 25 \(\upmu\)m.  
Figure 8 shows the changes in the microfibers for different skin lesion tissues, namely normal skin (Figure 8(a1,a2)), BE (Figure 8(b1,b2)), and MM (Figure 8(c1,c2)). The first row is the scalar retardance images, while the second row shows the vectorial retardance images. It has been reported that the scalar retardance values become smaller as normal tissue develops into BE and even MM [31,61]. This is consistent with the results shown in Figure 8(a1-c1). Correspondingly, the brightness gradually becomes darker in Figure 8(a2-c2). This is due to a loss of the inherent heterogeneity in the tissue morphology with the extent of the lesion [39].