title: Optic disc segmentation using the sliding band filter.
abstract: BACKGROUND
  The optic disc (OD) centre and boundary are important landmarks in retinal images and are essential for automating the calculation of health biomarkers related with some prevalent systemic disorders, such as diabetes, hypertension, cerebrovascular and cardiovascular diseases.
  
  
  METHODS
  This paper presents an automatic approach for OD segmentation using a multiresolution sliding band filter (SBF). After the preprocessing phase, a low-resolution SBF is applied on a downsampled retinal image and the locations of maximal filter response are used for focusing the analysis on a reduced region of interest (ROI). A high-resolution SBF is applied to obtain a set of pixels associated with the maximum response of the SBF, giving a coarse estimation of the OD boundary, which is regularized using a smoothing algorithm.
  
  
  RESULTS
  Our results are compared with manually extracted boundaries from public databases (ONHSD, MESSIDOR and INSPIRE-AVR datasets) outperforming recent approaches for OD segmentation. For the ONHSD, 44% of the results are classified as Excellent, while the remaining images are distributed between the Good (47%) and Fair (9%) categories. An average overlapping area of 83%, 89% and 85% is achieved for the images in ONHSD, MESSIDOR and INSPIR-AVR datasets, respectively, when comparing with the manually delineated OD regions.
  
  
  CONCLUSIONS
  The evaluation results on the images of three datasets demonstrate the better performance of the proposed method compared to recently published OD segmentation approaches and prove the independence of this method when from changes in image characteristics such as size, quality and camera field of view.
authors.affiliation: INEB - Instituto de Engenharia Biomédica, Universidade do Porto, Porto, Portugal; Faculdade de Engenharia, Universidade do Porto, Campus da FEUP, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: behdad.dashtbozorg@fe.up.pt.
authors.forename: Behdad
authors.initials: B
authors.lastname: Dashtbozorg
authors.affiliation: INEB - Instituto de Engenharia Biomédica, Universidade do Porto, Porto, Portugal; Faculdade de Engenharia, Universidade do Porto, Campus da FEUP, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: amendon@fe.up.pt.
authors.forename: Ana Maria
authors.initials: AM
authors.lastname: Mendonça
authors.affiliation: INESC TEC - INESC Technology and Science, Porto, Portugal; Faculdade de Engenharia, Universidade do Porto, Campus da FEUP, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal. Electronic address: campilho@fe.up.pt.
authors.forename: Aurélio
authors.initials: A
authors.lastname: Campilho
mesh_terms: D000465:Algorithms; D016208:Databases, Factual; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D061848:Optical Imaging / Q000295:instrumentation* / Q000379:methods*; D012160:Retina / Q000473:pathology*
keywords: Boundary extraction; Optic disc segmentation; Retinal images; Segmentation evaluation; Sliding band filter