title: Towards objective evaluation of the skin aspect: principles and instrumentation.
abstract: OBJECTIVE
  The aim of this paper is to propose an objective procedure for the evaluation of the skin aspect. This work is based on light scattering phenomena and in-vivo measurements of the skin profile and of the skin Bi-directional Reflection Distribution Function (BRDF).
  
  
  METHODS
  We consider the basic mechanisms of light reflection and scattering by a surface to extract the key sur-face-parameters of aspect. It appears that the surface relief is determinant for the local surface orientation while the light scattering properties of the skin are responsible for the visibility of that skin relief. The first part presents the principles of skin-image formation on the retina and de-scribes the actual roles of the BRDF and of the skin relief. The second part is dedicated to experimental measurements on the skin in vivo. The 3D relief is reconstructed by a fringe projection method and numerical processing. The angular distribution of light reflected by the skin is also measured by means of a different set-up.
  
  
  RESULTS
  The knowledge of both the skin relief obtained by 3D optical profilometry and the skin scattering behavior measured for regularly distributed set angle values, allows an objective aspect evaluation as well as a prediction of the skin images that an observer will receive.
  
  
  CONCLUSIONS
  This paper presents both the principles and instrumentation elements suitable for the setting up of an objective evaluation procedure of the skin aspect.
authors.affiliation: Département d'Optique PM Duffieux, Institut FEMTO-ST, UMR CNRS 6174, Université de Franche-Comté, Besançon, France. patrick.sandoz@univ-fcomte.fr
authors.forename: Patrick
authors.initials: P
authors.lastname: Sandoz
authors.forename: David
authors.initials: D
authors.lastname: Marsaut
authors.forename: Vincent
authors.initials: V
authors.lastname: Armbruster
authors.forename: Philippe
authors.initials: P
authors.lastname: Humbert
authors.forename: Tijani
authors.initials: T
authors.lastname: Gharbi
mesh_terms: D046169:Dermoscopy / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D012031:Refractometry / Q000295:instrumentation / Q000379:methods; D012867:Skin / Q000166:cytology*; D041622:Tomography, Optical / Q000295:instrumentation* / Q000379:methods*