## 3 Results and Discussion
### Discrimination of Different Human Skin Tissues Using Vectorial Retardance
#### 3.2.2 Qualitative Assessment by True-Color Vectorial Retardance Imaging
However, it can be found that vectorial retardance can provide higher contrast than scalar retardance, as shown in the area indicated by the red arrows in Figure 8. Thus, the inability to identify a single component does not hinder the ability of true-color vectorial retardance in assisting physicians in better differentiating different skin lesions. Additionally, depolarization [59] and diattenuation [89] are also of great value in disease identification. Their value has been studied in human basal cell carcinoma [90] and cervical precancerous lesions [91]. We believe that the true-color imaging method can also be extended to these parameters to analyze corresponding microstructure details. It is worth noting that the relatively small circular retardance contributes relatively weak to the true-color images than the linear retardance, as shown in Figure 5h, Figure 6f, and Figure 7(f1,f2). Because the true-color images are generated by simply overlaying the color channels in corresponding proportions of different components without any weight adjustment. The reason for the small presence of circular birefringence and chiral molecules is mainly due to the small thickness of the sections (4 \(\upmu\)m was used in this manuscript) [34]. It has been reported that linear retardance and circular retardance both are important tissue polarimetry characteristics [38; 92]. Linear retardance (or linear birefringence) of many tissues is stemming from their anisotropic fibrous structure, such as extra-cellular matrix proteins [93]. Circular retardance (or circular birefringence, also called optical rotation) in tissue arises due to the presence of asymmetric optically active chiral molecules such  
Figure 9: Imaging results of different stages of MM tissues: (**a1,a2**) early stage of MM; (**b1,b2**) intermediate stage of MM; (**c1,c2**) late stage of MM; (**a1–c1**) scalar retardance; (**a2–c2**) vectorial retardance. The scale bar represents 50 \(\upmu\)m.  
as glucose, proteins, and lipids [93; 94]. At present, many reports consider only linear retardance, which is largely dominant in tissues [33; 34; 70; 93; 94]. The major reason for the small circular retardance may result from the small thickness of the sections [34; 94], the small tissue anisotropy [70], or the resolution of the instrument. However, the measurement of optical rotation (circular birefringence) may provide an attractive method for pathological diagnosis [70]. Furthermore, together, \(R_{C}\), \(R_{H}\), and \(R_{45}\) are indispensable components of the vectorial retardance describing the complete birefringent characteristics of anisotropic structures (magnitude and fast axis) [56]. Therefore, vectorial retardance imaging technology combining the three retardance components simultaneously is necessary for analyzing anisotropic microstructures. In our experiment, although the \(R_{C}\) shows a smaller magnitude compared to the linear retardance, the \(R_{C}\) model trained using five characteristics with specific statistics significance (including \(M\), \(S_{td}\), \(S_{ke}\), \(K_{ur}\), and \(E_{n}\)) have comparable classification ability with linear retardance. The cross-validation accuracy and prediction accuracy in distinguishing MM an BE and normal skin can be achieved at 88.33% and 85.92%, respectively. This proves that feature mining and quantitative classification using the SVM can compensate for the limitations of subjective judgment. The experimental results from [29] demonstrate circular birefringence of skin tissues, although small (\(\sim\)0.25 rad), is present in the normal skin tissues. We attribute the small presence of circular birefringence and chiral molecules to the small thickness of the sections (5 \(\upmu\)m was used in the reported study [29]). The authors of [62] reported that circular retardance components can be used to classify different cervical lesions [62]. That is due to the optically active collagen fibers present in the stroma of cervical tissue [62].