Tuesday, March 3, 2009

Polar View of an Image

Article From Codeproject

Image warping gives interesting results. Many special effects can be achieved through image warping. Warping is a process where an image is transformed in some way, to arrive at another image. This is as though the image is printed on a rubber sheet and that sheet is stretched in a non-uniform way. Polar mapping is an example of image warping. This is similar to the standard Log Polar mapping available in image processing. The receptor distribution in the retina of our eye resembles a log polar array. The difference between a log polar map and a polar map is that the concentric circles are non-uniformly spaced in a log polar map, whereas they are uniformly spaced in a polar map. In this article, we illustrate code to do polar mapping of an image.

Polar Mapping

The basic geometry of polar mapping is shown in the figure below. Equally spaced concentric circles are drawn centered at the image centre, and a number of equally spaced sectors are drawn. Pixels at the points of intersection of these circles and radial lines are plotted on a rectangular grid, and the resulting image is a polar view. In a log polar mapping, the radii of the concentric circles vary on a logarithmic scale.



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