title: Quantifying facial skin erythema more precisely by analyzing color channels of The VISIA Red images.
abstract: BACKGROUND
  The VISIA Red images were developed to document and measure facial skin erythema, but diffuse erythema cannot be fully segmented by the VISIA system due to the automatic thresholding segmentation method. Moreover, topical area analysis is not available in the system.
  
  
  METHODS
  Erythema severity degrees of 20 simulated Red images were designated 1-20 with 1-20 inflammatory lesions for each, respectively. The RGB channel mean values of each simulated image were acquired by ImageJ and relative intensity of red values calculated.
  
  
  RESULTS
  The relative intensity of red values positively correlate to erythema severity with a coefficient of 0.999345 (p < 0.001). We also proposed a method for calibration when pustules were present in the erythema area. The method was proved by mathematical reasoning and verified by certified dermatologists.
  
  
  CONCLUSIONS
  We demonstrated a simple and more precise method to quantify and compare facial skin erythema by analyzing the RGB channel values of the VISIA Red images. Our method brings convenience for erythema evaluation in dermatological studies.
authors.affiliation: a Department of Dermatology at No.1 Hospital , Anhui Medical University , Hefei , China.|b Department of Dermatology , The PLA General Hospital of Air Force , Beijing , China.
authors.forename: De-Tian
authors.initials: DT
authors.lastname: Xu
authors.affiliation: c Shanghai Dermatology Hospital , Shanghai , China.
authors.forename: Jian-Na
authors.initials: JN
authors.lastname: Yan
authors.affiliation: d Institute of Dermatology and Department of Dermatology at No.1 Hospital , Anhui Medical University , Hefei , China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Cui
authors.affiliation: b Department of Dermatology , The PLA General Hospital of Air Force , Beijing , China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
mesh_terms: D003124:Colorimetry / Q000295:instrumentation*; D004890:Erythema / Q000145:classification*; D005145:Face; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D012880:Skin Pigmentation
keywords: Color channel analysis; VISIA Red image; erythema quantification; skin analysis