Abstract
PurposeSignificant research has been carried out in terms of development of new bidirectional reflectance distribution function (BRDF) instruments; however, there is still little research available regarding spectral BRDF measurements of human skin. This study aims to investigate the variation in human skin reflectance using a new fibre optic-based spectral-BRDF measurement device.Design/methodology/approachDesign of this system mainly involves use of multiple fibre optics to illuminate and detect light reflected from a sample, whereas a hemispherical dome was 3D printed to mount the fibres at various slant/tilt angles. To investigate the spectral differences in BRDF of human skin, 3 narrowband filters in the visible spectrum were used, whereas measurements were taken from the back of the hand for Caucasian and Asian skin types.FindingsThe experiments demonstrate that the BRDF of human skin varies with wavelengths in the visible spectrum and it is also different for Caucasian and Asian skin types. Both skin types exhibit off-specular reflection with increase in angle of incidence and show less variation with respect to viewing angles when the angle of incidence is normal to the surface.Research implicationsA database of spectral BRDF measurements of human skin will help not only in creating realistic skin renderings but also in development of novel skin reflectance models for biomedical and machine vision applications. The measurements would also provide means to validate the predictions from existing light transport/spectral simulation models for human skin and will ultimately help in the accurate diagnosis and simulation of various skin disorders.Originality/valueThe proposed system provides fast scatter measurements by utilising multiple fibres to detect light simultaneously at different angles while also allowing easy switching between incident light directions. Due to its flexible design and contact-based measurements, the device is independent of errors due to sample movements and does not require any image registration. Also, measurements taken from the device show that the BRDF of skin varies significantly in the visible spectrum and it is different for Caucasian and Asian skin types.
Highlights
As light interacts with a surface, some of it is transmitted through the material, some gets absorbed and the rest is reflected
We propose the use of a fibre optic based device that can be used to create a large database of spectral-Bidirectional Reflectance Distribution Function (BRDF) measurements of human skin and we present measurements of different skin types over narrowband wavelengths to show variations in BRDF in the visible spectrum
We present a prototype device that has the potential to provide reliable spectral BRDF information for human skin and can be used to create a large database of human skin measurements
Summary
As light interacts with a surface, some of it is transmitted through the material, some gets absorbed and the rest is reflected. We propose the use of a fibre optic based device that can be used to create a large database of spectral-BRDF measurements of human skin and we present measurements of different skin types over narrowband wavelengths to show variations in BRDF in the visible spectrum. The detector used in these devices is usually based on spectroradiometers/diode-arrays and can provide better precision/sensitivity to light variation as compared to the image based techniques Since these devices make use of multi-axis motorised stages/robots (Belcour et al.2014; Hünerhoff et al 2006) to move around the light source, detector and sample, it makes the capture process slow (tens of hours) and impractical for human skin measurements. Given the 3D model of the sample, the illumination and viewing directions relative to a number of different surface normals allowed them to capture the BRDF in relatively less time than traditional gonioreflectometer measurements. We present a prototype device that has the potential to provide reliable spectral BRDF information for human skin and can be used to create a large database of human skin measurements
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