title: Retinal slit lamp video mosaicking.
abstract: OBJECTIVE
  To this day, the slit lamp remains the first tool used by an ophthalmologist to examine patient eyes. Imaging of the retina poses, however, a variety of problems, namely a shallow depth of focus, reflections from the optical system, a small field of view and non-uniform illumination. For ophthalmologists, the use of slit lamp images for documentation and analysis purposes, however, remains extremely challenging due to large image artifacts. For this reason, we propose an automatic retinal slit lamp video mosaicking, which enlarges the field of view and reduces amount of noise and reflections, thus enhancing image quality.
  
  
  METHODS
  Our method is composed of three parts: (i) viable content segmentation, (ii) global registration and (iii) image blending. Frame content is segmented using gradient boosting with custom pixel-wise features. Speeded-up robust features are used for finding pair-wise translations between frames with robust random sample consensus estimation and graph-based simultaneous localization and mapping for global bundle adjustment. Foreground-aware blending based on feathering merges video frames into comprehensive mosaics.
  
  
  RESULTS
  Foreground is segmented successfully with an area under the curve of the receiver operating characteristic curve of 0.9557. Mosaicking results and state-of-the-art methods were compared and rated by ophthalmologists showing a strong preference for a large field of view provided by our method.
  
  
  CONCLUSIONS
  The proposed method for global registration of retinal slit lamp images of the retina into comprehensive mosaics improves over state-of-the-art methods and is preferred qualitatively.
authors.affiliation: ARTORG Research Center Biomedical Engineering Research, University of Bern, Murtenstrasse 50, 3008, Bern, Switzerland.
authors.forename: Sandro
authors.initials: S
authors.lastname: De Zanet
authors.affiliation: ARTORG Research Center Biomedical Engineering Research, University of Bern, Murtenstrasse 50, 3008, Bern, Switzerland.
authors.forename: Tobias
authors.initials: T
authors.lastname: Rudolph
authors.affiliation: Seecrypt, Witch-Hazel Ave, Centurion, 0169, South Africa.
authors.forename: Rogerio
authors.initials: R
authors.lastname: Richa
authors.affiliation: Department of Ophthalmology, Inselspital Bern, Freiburgstrasse 12, 3010, Bern, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Tappeiner
authors.affiliation: ARTORG Research Center Biomedical Engineering Research, University of Bern, Murtenstrasse 50, 3008, Bern, Switzerland. raphael.sznitman@artorg.unibe.ch.
authors.forename: Raphael
authors.identifier: http://orcid.org/0000-0001-6791-4753
authors.initials: R
authors.lastname: Sznitman
mesh_terms: D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D012160:Retina / Q000000981:diagnostic imaging*; D000072776:Slit Lamp Microscopy / Q000379:methods*; D014741:Video Recording
keywords: Blending; Mosaicking; Slit lamp; Tracking