# Creating a Diagnostic Assistance System for Diseases in Kampo Medicine
## 2 Materials and Methods  
### Capturing Glossy and Non-Glossy Images Using Polarized Light  
Incident light from a source is reflected from the surface of an object. This reflection of the light is classified into two types: surface reflection, where the angles of incidence and reflection of light are the same with respect to the surface of reflection, and internal diffuse reflection caused by the scattering of the incident light inside the object. The human eye and a camera perceive the color and luster of an object by capturing the reflected light. In general, an object appears colored owing to internal diffuse reflection, while luster is caused by surface reflection. Light is an electromagnetic wave that oscillates in a direction perpendicular to its direction of travel, and normal light is in an unpolarized or partially polarized state, which is a mixture of light oscillating in all directions. Polarization, conversely, refers to light that oscillates only in a certain direction. Passing ordinary unpolarized light through an optical filter called a polarizing plate creates polarized light in a direction identical to that of the polarizing plate.  
This property of polarization has important links to the surface reflection and internal diffusion. Light is reflected while the polarization of the incident light is maintained; when the incident light is reflected off the surface of the object, it is linearly polarized in the direction of the polarizing plate, as in the case of incident light. Conversely, internal diffuse light is unpolarized even if the incident light is linearly polarized when internally reflected, because the incident light is reflected in various directions and the light is scattered. We used this property to obtain glossy and non-glossy images.  
Figure 1 shows the method used to obtain an image with enhanced gloss and one with reduced gloss using two orthogonal polarizing plates. \(S\) indicates the surface-reflected light, \(D\) indicates diffuse reflected light, and the subscripts \(p\) and \(s\) indicate the directions of orthogonal polarization. Since \(S\) in Figure 1a maintains the same polarization as the incident light, the relationship between the intensity of \(S\) and that of the p-polarization component (\(S_{p}\)) of \(S\) is shown in Equation (1), where \(I_{x}\) indicates the intensity of \(x\):  
\[I_{S}=I_{S_{p}} \tag{1}\]  
The diffuse component (\(D\)) in Figure 1a is the loss of polarization of the incident light. The ratio of intensity of the p-polarization component \(\left(D_{p}\right)\) to that of the s-polarization component (\(D_{s}\)) in \(D\) is 1:1, and can be expressed as:  
\[I_{D}=I_{D_{p}}+I_{D_{s}}=2I_{D_{p}}=2I_{D_{s}} \tag{2}\]Figure 1b shows the setup used to attain a gloss-enhanced image by placing a second polarizing plate between the object and the camera. When light passes through the p-polarizing plate, the component of s-polarization in the vertical direction cannot pass through the p-polarizing plate. Thus, the internally reflected light (\(D\)), which contains \(D_{s}\), has half the intensity; however, \(S_{p}\), which has only the p-polarization component, can pass through the p-polarizing plate illumination and the object. In the present study, we used a polarizing camera instead of a second polarizing plate placed in front of the camera. The polarizing camera can capture 0\({}^{\circ}\), 45\({}^{\circ}\), 90\({}^{\circ}\), and 145\({}^{\circ}\) polarization images simultaneously, enabling the capture of a gloss-enhanced image from a 0\({}^{\circ}\) polarization image and a non-glossy image from a 90\({}^{\circ}\) polarization image simultaneously.