title: Validation of image analysis techniques to measure skin aging features from facial photographs.
abstract: BACKGROUND
  Accurate measurement of the extent skin has aged is crucial for skin aging research. Image analysis offers a quick and consistent approach for quantifying skin aging features from photographs, but is prone to technical bias and requires proper validation.
  
  
  METHODS
  Facial photographs of 75 male and 75 female North-European participants, randomly selected from the Rotterdam Study, were graded by two physicians using photonumeric scales for wrinkles (full face, forehead, crow's feet, nasolabial fold and upper lip), pigmented spots and telangiectasia. Image analysis measurements of the same features were optimized using photonumeric grades from 50 participants, then compared to photonumeric grading in the 100 remaining participants stratified by sex.
  
  
  RESULTS
  The inter-rater reliability of the photonumeric grades was good to excellent (intraclass correlation coefficients 0.65-0.93). Correlations between the digital measures and the photonumeric grading were moderate to excellent for all the wrinkle comparisons (Spearman's rho ρ = 0.52-0.89) bar the upper lip wrinkles in the men (fair, ρ = 0.30). Correlations were moderate to good for pigmented spots and telangiectasia (ρ = 0.60-0.75).
  
  
  CONCLUSIONS
  These comparisons demonstrate that all the image analysis measures, bar the upper lip measure in the men, are suitable for use in skin aging research and highlight areas of improvement for future refinements of the techniques.
authors.affiliation: Department of Dermatology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.|Netherlands Genomics Initiative (NGI) - sponsored Netherlands Consortium for Healthy Aging (NCHA), Leiden, The Netherlands.
authors.forename: M A
authors.initials: MA
authors.lastname: Hamer
authors.affiliation: Department of Dermatology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.|Netherlands Genomics Initiative (NGI) - sponsored Netherlands Consortium for Healthy Aging (NCHA), Leiden, The Netherlands.
authors.forename: L C
authors.initials: LC
authors.lastname: Jacobs
authors.affiliation: Unilever Research and Development, Colworth Science Park, Sharnbrook, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: Lall
authors.affiliation: Section of Evolutionary Biology, Department of Biology II, University of Munich, Planegg-Martinsried, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Wollstein
authors.affiliation: Department of Dermatology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: L M
authors.initials: LM
authors.lastname: Hollestein
authors.affiliation: Tessella, Abingdon, UK.
authors.forename: A R
authors.initials: AR
authors.lastname: Rae
authors.affiliation: Formerly Unilever R&D, Trumbull, CT, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Gossage
authors.affiliation: Department of Epidemiology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Hofman
authors.affiliation: Department of Forensic Molecular Biology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: F
authors.initials: F
authors.lastname: Liu
authors.affiliation: Department of Forensic Molecular Biology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Kayser
authors.affiliation: Department of Dermatology, Erasmus MC University Medical Center Rotterdam, Rotterdam, The Netherlands.|Netherlands Genomics Initiative (NGI) - sponsored Netherlands Consortium for Healthy Aging (NCHA), Leiden, The Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Nijsten
authors.affiliation: Unilever Research and Development, Colworth Science Park, Sharnbrook, UK.
authors.forename: D A
authors.initials: DA
authors.lastname: Gunn
mesh_terms: D005145:Face / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010363:Pattern Recognition, Automated / Q000379:methods*; D010781:Photography / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D015595:Skin Aging / Q000473:pathology*
keywords: Digital; Grading scale; Photonumeric; Pigmented spots; Skin aging; Telangiectasia; Wrinkles