title: Single-image vignetting correction from gradient distribution symmetries.
abstract: We present novel techniques for single-image vignetting correction based on symmetries of two forms of image gradients: semicircular tangential gradients (SCTG) and radial gradients (RG). For a given image pixel, an SCTG is an image gradient along the tangential direction of a circle centered at the presumed optical center and passing through the pixel. An RG is an image gradient along the radial direction with respect to the optical center. We observe that the symmetry properties of SCTG and RG distributions are closely related to the vignetting in the image. Based on these symmetry properties, we develop an automatic optical center estimation algorithm by minimizing the asymmetry of SCTG distributions, and also present two methods for vignetting estimation based on minimizing the asymmetry of RG distributions. In comparison to prior approaches to single-image vignetting correction, our methods do not rely on image segmentation and they produce more accurate results. Experiments show our techniques to work well for a wide range of images while achieving a speed-up of 3-5 times compared to a state-of-the-art method.
authors.affiliation: Department of Radiology, University of Pennsylvania, 3600 Market St., Suite 370, Philadelphia, PA 19104-2644, USA. Yuanjie.Zheng@uphs.upenn.edu
authors.forename: Yuanjie
authors.initials: Y
authors.lastname: Zheng
authors.forename: Stephen
authors.initials: S
authors.lastname: Lin
authors.forename: Sing Bing
authors.initials: SB
authors.lastname: Kang
authors.forename: Rui
authors.initials: R
authors.lastname: Xiao
authors.forename: James C
authors.initials: JC
authors.lastname: Gee
authors.forename: Chandra
authors.initials: C
authors.lastname: Kambhamettu
mesh_terms: D000465:Algorithms; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods*