title: Chromatic aberration correction: an enhancement to the calibration of low-cost digital dermoscopes.
abstract: OBJECTIVE
  We present a method for calibrating low-cost digital dermoscopes that corrects for color and inconsistent lighting and also corrects for chromatic aberration. Chromatic aberration is a form of radial distortion that often occurs in inexpensive digital dermoscopes and creates red and blue halo-like effects on edges. Being radial in nature, distortions due to chromatic aberration are not constant across the image, but rather vary in both magnitude and direction. As a result, distortions are not only visually distracting but could also mislead automated characterization techniques.
  
  
  METHODS
  Two low-cost dermoscopes, based on different consumer-grade cameras, were tested. Color is corrected by imaging a reference and applying singular value decomposition to determine the transformation required to ensure accurate color reproduction. Lighting is corrected by imaging a uniform surface and creating lighting correction maps. Chromatic aberration is corrected using a second-order radial distortion model.
  
  
  RESULTS
  Our results for color and lighting calibration are consistent with previously published results, while distortions due to chromatic aberration can be reduced by 42-47% in the two systems considered.
  
  
  CONCLUSIONS
  The disadvantages of inexpensive dermoscopy can be quickly substantially mitigated with a suitable calibration procedure.
authors.affiliation: School of Computing Science, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: Paul
authors.initials: P
authors.lastname: Wighton
authors.forename: Tim K
authors.initials: TK
authors.lastname: Lee
authors.forename: Harvey
authors.initials: H
authors.lastname: Lui
authors.forename: David
authors.initials: D
authors.lastname: McLean
authors.forename: M Stella
authors.initials: MS
authors.lastname: Atkins
mesh_terms: D016477:Artifacts; D002138:Calibration; D002170:Canada; D003124:Colorimetry / Q000295:instrumentation / Q000592:standards*; D046169:Dermoscopy / Q000295:instrumentation* / Q000592:standards*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007090:Image Interpretation, Computer-Assisted / Q000295:instrumentation / Q000592:standards*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity