Background: The brightness of skin is affected by surface reflection and subsurface reflection. It has been found that the subsurface reflection comprises more than 90% of the light reflected from the skin and is associated with the dermal micro-structures, such as collagen fiber.
Objective: The aim of study was to investigate which histologic characteristics of dermis are related to the brightness of skin. 
Materials and Methods: Total 15 cadavers were examined for photographs and skin specimens. Colorimetric images of each site were photographed without polarized light using funnel-shaped spacer. And, the photos using crossed-polarized light (CPL) with white and green light emitting diode (LED) were obtained. The RGB values of image were measured and converted to CIELAB values. After skin specimens were taken, they were processed with Masson‘s trichrome (MT) stain and hematoxylin & eosin (H&E) stain. These slides were photographed with the optical microscope connected to digital camera and the images were used for measurements. MT stained slides were analyzed to investigate the density of collagen fibers using color thresholding method, the function of image analysis software. Other histologic features were measured in H&E stained slides. Correlational analysis was performed to determine the relationship between the measured CIELAB values and the measured histologic features.
Results: : The L*value of colorimetric images had positive correlations with the density of collagen fibers, the thickness of dermis and showed a negative correlation with the thickness of epidermis. The L*value of white CPL images showed positive correlations with the diameter of reticular collagen, the thickness of dermis, and a negative correlation with the depth of dermo-epidermal junction. The L*values of green CPL images had positive correlations with the density of collagen fibers, the diameter of reticular collagen, the thickness of dermis, and showed a negative correlation with the thickness of epidermis.
Conclusion: According to the findings, the skin brightness was related with the properties of dermal structures, such as density and diameter of collagen, thickness of dermis. With further research, it is possible to enhance the brightness of skin by modifying dermal micro-structures.

The effect of dermal microscopic parameters on the optical skin properties: the analysis using crossed polarized light imaging on fresh cadavers