title: Effect of image quality, color, and format on the measurement of retinal vascular fractal dimension.
abstract: OBJECTIVE
  Fractal dimension of retinal vasculature is a global summary measure of retinal vascular network pattern and geometry. This study was conducted to examine the effect of variations in image color, brightness, focus, contrast, and format on the measurement of retinal vascular fractal dimension.
  
  
  METHODS
  A set of 30 retinal images from the Blue Mountains Eye Study was used for a series of experiments by varying brightness, focus (blur), contrast, and color (color versus monochrome). The original and the modified images were graded for fractal dimension (D(f)) using dedicated retinal imaging software (IRIS-Fractal). A further set of 20 grayscale images was used to compare image format (.jpg versus .tif) with regard to the resultant D(f) and processing time.
  
  
  RESULTS
  The mean D(f) of original images in this sample was 1.454. Compared with the original set of images, variations in brightness, focus, contrast, and color affected the measurements to a small to moderate degree (Pearson correlation coefficient, r, ranged from 0.47 to 0.97). Very dark or blurry images resulted in a substantially lower estimate of D(f). Monochrome images were also consistently associated with lower D(f) compared with that obtained from color images. Using .jpg or .tif image formats did not affect the measurement or the time needed to process and measure D(f).
  
  
  CONCLUSIONS
  Variations in image brightness, focus, and contrast can significantly affect the measurement of retinal vascular fractals. Standardization of image parameters and consistent use of either monochrome or color images would reduce measurement noise and enhance the comparability of the results.
authors.affiliation: Department of Ophthalmology, Centre for Vision Research, Westmead Millennium Institute, University of Sydney, Sydney, Australia;
authors.forename: Alan
authors.initials: A
authors.lastname: Wainwright
authors.forename: Gerald
authors.initials: G
authors.lastname: Liew
authors.forename: George
authors.initials: G
authors.lastname: Burlutsky
authors.forename: Elena
authors.initials: E
authors.lastname: Rochtchina
authors.forename: Yong Ping
authors.initials: YP
authors.lastname: Zhang
authors.forename: Wynne
authors.initials: W
authors.lastname: Hsu
authors.forename: Janice MongLi
authors.initials: JM
authors.lastname: Lee
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.forename: Paul
authors.initials: P
authors.lastname: Mitchell
authors.forename: Jie Jin
authors.initials: JJ
authors.lastname: Wang
mesh_terms: D003116:Color; D017709:Fractals; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted / Q000592:standards*; D010781:Photography; D015203:Reproducibility of Results; D012171:Retinal Vessels / Q000033:anatomy & histology*