In vivo measurement of skin microrelief using photometric stereo in the presence of interreflections

Ali Sohaib,Lyndon N Smith,Robert Warr,Melvyn L Smith,Gary A Atkinson,Abdul R Farooq

doi:10.1364/josaa.30.000278

Abstract

This paper proposes and describes an implementation of a photometric stereo-based technique for in vivo assessment of three-dimensional (3D) skin topography in the presence of interreflections. The proposed method illuminates skin with red, green, and blue colored lights and uses the resulting variation in surface gradients to mitigate the effects of interreflections. Experiments were carried out on Caucasian, Asian, and African American subjects to demonstrate the accuracy of our method and to validate the measurements produced by our system. Our method produced significant improvement in 3D surface reconstruction for all Caucasian, Asian, and African American skin types. The results also illustrate the differences in recovered skin topography due to the nondiffuse bidirectional reflectance distribution function (BRDF) for each color illumination used, which also concur with the existing multispectral BRDF data available for skin.

Highlights

Since the emergence of photometric stereo [1], the technique has developed into a recognized approach for three dimensional 3D object shape recovery using a relatively simple methodology
Numerous studies involving the analysis of skin microrelief using photometric stereo has been conducted in the past decade, some are based on real time imaging whilst most are limited to static analysis
This variation in Bidirectional reflectance distribution function (BRDF) explains the variation in shape estimation from each color light at the concave parts of the skin where we found both over and under estimation of depth

Summary

Introduction

Since the emergence of photometric stereo [1], the technique has developed into a recognized approach for three dimensional 3D object shape recovery using a relatively simple methodology. Photometric stereo uses a single sensor and multiplexed light to achieve multiple images of the same scene with differences only in the source lighting directions. Most concave surfaces exhibit such behavior, as light bounces multiple times between patches on the surface before returning to the viewer This phenomenon creates problems for shape for shading techniques, which for a given albedo assume that the surface normal alone at a point defines the reflected radiance. Liao [8] used this distinction to separate direct and indirect reflected light by using colored lights to vary surface albedo They did assume surface reflection to be Lambertian, which is a prevailing assumption associated with skin when using shape from shading algorithms. The following is a summary of key contributions of this paper

Methods

Findings

Discussion

Conclusion