Image-based control of skin translucency

Comprehensive model for characterizing skin translucency by expert grading, panel evaluation and image analysis in a Chinese population

OBJECTIVES

Translucent skin is an attribute widely appreciated by people in East Asian countries. There have been studies in the literature to describe the phenomenon by means of clinical grading, instrumental measurement, and image analysis. However, due to its subjective and complex nature, skin translucency has not been comprehensively and rigorously characterized and modeled, particularly in the Chinese population. This study is to develop a mathematical model that quantitatively describes skin translucency from visual cues objectively measured from the skin.

MATERIALS AND METHODS

The study was designed to characterize and model skin translucency by incorporating expert evaluation, panel perception and image analysis of multiple skin visual attributes in one analysis. Faces of 36 Chinese females aged 18-65 years old were evaluated by a dermatologist to obtain clinical translucency scores. Subject pairs were formed with a relatively high and low translucency score in each pair. Their faces were judged in person by 9 panelists in paired-comparison (2-AFC) fashion to pick a "more translucent skin" from each subject pair. Front-view facial images of the subjects were taken, and multiple color and other visually perceivable skin attributes were measured using image analysis. Bradley-Terry analysis and multiple regressions were performed to correlate the panel choices of "more translucent skin" with the objectively measured skin parameters.

RESULTS

Multiple skin color properties affected the panel choices toward translucent skin. Among them skin tone lightness and skin glossiness had positive effects on skin translucency while the hue, color unevenness, severity of red and dark spots affected it negatively. Subsurface light reflection and skin visual smoothness had some effect but were not statistically significant. A mathematical model was constructed to predict a person's skin translucency from objectively measured skin attributes.

CONCLUSION

The subjective property of skin translucency can be characterized and quantified via a comprehensive modeling process involving clinical grading, panel evaluation, image-based measurement of skin attributes and statistical analysis. A novel skin parameter, Skin Translucency Index (STI) was established which provides a way to measure skin translucency, making it possible to assess treatment efficacy before and after product application.

Digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA)

Single-shot digital holography based on multiwavelength spatial-bandwidth-extended capturing-technique using a reference arm (Multi-SPECTRA) is proposed. Both amplitude and quantitative phase distributions of waves containing multiple wavelengths are simultaneously recorded with a single reference arm in a single monochromatic image. Then, multiple wavelength information is separately extracted in the spatial frequency domain. The crosstalk between the object waves with different wavelengths is avoided and the number of wavelengths recorded with both a single-shot exposure and no crosstalk can be increased, by a large spatial carrier that causes the aliasing, and/or by use of a grating. The validity of Multi-SPECTRA is quantitatively, numerically, and experimentally confirmed.

Rapid and accurate estimation of blood saturation, melanin content, and epidermis thickness from spectral diffuse reflectance

We present a method to determine chromophore concentrations, blood saturation, and epidermal thickness of human skin from diffuse reflectance spectra. Human skin was approximated as a plane-parallel slab of variable thickness supported by a semi-infinite layer corresponding to the epidermis and dermis, respectively. The absorption coefficient was modeled as a function of melanin content for the epidermis and blood content and oxygen saturation for the dermis. The scattering coefficient and refractive index of each layer were found in the literature. Diffuse reflectance spectra between 490 and 620 nm were generated using Monte Carlo simulations for a wide range of melanosome volume fraction, epidermal thickness, blood volume, and oxygen saturation. Then, an inverse method was developed to retrieve these physiologically meaningful parameters from the simulated diffuse reflectance spectra of skin. A previously developed accurate and efficient semiempirical model for diffuse reflectance of two layered media was used instead of time-consuming Monte Carlo simulations. All parameters could be estimated with relative root-mean-squared error of less than 5% for (i) melanosome volume fraction ranging from 1% to 8%, (ii) epidermal thickness from 20 to 150 mum, (iii) oxygen saturation from 25% to 100%, (iv) blood volume from 1.2% to 10%, and (v) tissue scattering coefficient typical of human skin in the visible part of the spectrum. A similar approach could be extended to other two-layer absorbing and scattering systems.