## 3 Results and Discussion
### Discrimination of Different Human Skin Tissues Using Vectorial Retardance
#### 3.2.2 Qualitative Assessment by True-Color Vectorial Retardance Imaging
This indicates that the highly organized fibrous structure of the normal tissue is most likely obliterated by various pathologies such as BE and MM [61]. Such changes can be directly observed by the orientation of fibers in Figure 8(a2-c2). As in the area indicated by red arrows in Figure 8(b2), the BE shows a  
Figure 7: Imaging results of BE and MM tissues: (**a1–f1**) BE; (**a2–f2**) MM; (**a1,a2**) horizontal retardance; (**b1,b2**) 45\({}^{\circ}\)-linear retardance; (**c1,c2**) circle retardance; (**d1,d2**) microscopic intensity image of H&E stained section; (**e1,e2**) scalar retardance; (**f1,f2**) vectorial retardance. The scale bar represents 50 \(\upmu\)m.  
relatively ordered orientation but with much thinner fibrous stripes, whereas Figure 8(c2) shows a large number of scattered dotted fibers in MM tissue. We suspect that during the development of BE, the main mode of degradation is the transformation of bundled fibers into thin fibrils. In MM, the severe breakage of fibrils plays a leading role. This finding needs to be further verified by histology. Nevertheless, all these assumptions do not hinder the ability to infer and generalize the results of the true-color vectorial retardance imaging technique from the perspective of skin tissues and associated pathologies. The true-color vectorial retardance imaging method can assist the physician to better identify different lesions by enhancing the image contrast. As shown in Figure 8(a2,b2,c2), as the lesions increase, the collagen fibers become severely degraded, resulting in a weakening of the birefringence property [31; 61]. Thus, the brightness of the vectorial retardance image gradually becomes darker, and the fracture of the fibers is better highlighted than the scalar retardance. Figure 9 shows the MMIP imaging results of different stages of MM tissues. Figure 9(a2-c2) gives the true-color vectorial retardance images for the early, intermediate, and late stages of MM unstained sections. Compared with scalar retardance, true-color vectorial retardance imaging reflects not only the distribution but also the orientation of fibers in higher image contrast and clarity. By the vectorial retardance images, it can be found that the fiber content decreases, and the breakage becomes more severe as the degree of MM increases, which is due to the degradation of fibers resulting from the tumor expansion. These findings demonstrate that true-color vectorial retardance may assist the clinician in providing additional information regarding the stage of MM. In the future, we will study in depth the correspondence between different lesions and true-color vectorial retardance images. Although scalar retardance is utilized widely in diagnosing lesions [33; 35; 36; 37], the visualization of fiber distribution is limited and with less tissue-specificity contrast [47; 69]. The orientation of linear retardance, another important parameter for observing the ori  
Figure 8: Imaging results of normal skin, BE, and MM tissues: (**a1,a2**) normal skin; (**b1,b2**) BE; (**c1,c2**) MM; (**a1–c1**) scalar retardance; (**a2–c2**) vectorial retardance. The scale bar represents 50 \(\upmu\)m.  
entations of anisotropic fibers, is usually paired with scalar retardance to describe the birefringence [32]. However, it is inconvenient and time-consuming to read and analyze the two parameters simultaneously. In contrast to scalar retardance, the true-color vectorial retardance imaging method can directly distinguish the lesion and reflect the orientation of fibers with high contrast. As shown in the upper Figure 8(a2-c2) and Figure 9(a2-c2), it is difficult to distinguish each of the three components in a single vectorial retardance image. Because the true-color vectorial retardance algorithm used color and brightness to highlight the orientation and distribution information, by combining the three components together.