An Image based auto-focusing algorithm fordigital fundus photography

Michele Moscaritolo, Henry D Jampel, Frederick Knezevich, Ran Zeimer

Research output: Contribution to journalArticle

Abstract

In fundus photography, the task of fine focusing the image is demanding and lack of focus is quite often the cause of suboptimal photographs. The introduction of digital cameras has provided an opportunity to automate the task of focusing. We have developed a software algorithm capable of identifying best focus. The auto-focus (AF) method is based on an algorithm we developed to assess the sharpness of an image. The AF algorithm was tested in the prototype of a semi-automated nonmydriatic fundus camera designed to screen in the primary care environment for major eye diseases. A series of images was acquired in volunteers while focusing the camera on the fundus. The image with the best focus was determined by the AF algorithm and compared to the assessment of two masked readers. A set of fundus images was obtained in 26 eyes of 20 normal subjects and 42 eyes of 28 glaucoma patients. The 95% limits of agreement between the readers and the AF algorithm were ${-}2.56$ to 2.93 and ${-}3.7$ to 3.84 diopter and the bias was 0.09 and 0.71 diopter, for the two readers respectively. On average, the readers agreed with the AF algorithm on the best correction within less than $3/4$ diopter. The intraobserver repeatability was 0.94 and 1.87 diopter, for the two readers respectively, indicating that the limit of agreement with the AF algorithm was determined predominantly by the repeatability of each reader. An auto-focus algorithm for digital fundus photography can identify the best focus reliably and objectively. It may improve the quality of fundus images by easing the task of the photographer.

Original languageEnglish (US)
Article number4813255
Pages (from-to)1703-1707
Number of pages5
JournalIEEE Transactions on Medical Imaging
Volume28
Issue number11
DOIs
StatePublished - Nov 2009

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Photography
Eye Diseases
Glaucoma
Cameras
Volunteers
Primary Health Care
Software
Digital cameras

Keywords

  • Digital fundus photography
  • Focus
  • Image processing
  • Sharpness

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Computer Science Applications
  • Radiological and Ultrasound Technology
  • Software

Cite this

An Image based auto-focusing algorithm fordigital fundus photography. / Moscaritolo, Michele; Jampel, Henry D; Knezevich, Frederick; Zeimer, Ran.

In: IEEE Transactions on Medical Imaging, Vol. 28, No. 11, 4813255, 11.2009, p. 1703-1707.

Research output: Contribution to journalArticle

Moscaritolo, Michele ; Jampel, Henry D ; Knezevich, Frederick ; Zeimer, Ran. / An Image based auto-focusing algorithm fordigital fundus photography. In: IEEE Transactions on Medical Imaging. 2009 ; Vol. 28, No. 11. pp. 1703-1707.
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