Big Ben's Panorama Tutorials

Remapping and Noise

One of the things that people complain about with film scans from circular fisheye lenses is the increased amount of grain (noise), particularly in the sky. Increasing the number of images used (and thus the amount of image overlap) does not solve the problem... and this is because the amount of horizontal overlap has very little to do with the zenith or nadir. Note that this problem also applies to images from digital cameras, although the amount of noise is usually lower.

With a single row of fisheye images of 180, the zenith and nadir will always be at the edge of the image. Increasing the number of horizontal images improves the image quality around the centre of the panorama, but not at the top and bottom.

Test patternTo illustrate this let's take an image that consists of concentric coloured circles with a grid of 1 pixel black squares representing image noise.. The black circle represents the image circle of a fisheye lens with an FOV of 180.  When the image is remapped to an equirectangular projection the portions of the image near the edges get distorted more than those near the centre.

Remapped test imageSince the FOV is 180, remapping this to an equirectangular projection will create a square. The test image below uses the same distortion settings for my Sigma lens (a-0.2 b0.3 c-0.2)

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This page, its contents and style, are the responsibility of the author and do not represent the views, policies or opinions of The University of Melbourne. All photographs Ben Kreunen 2000

Ben Kreunen <bernardk@unimelb.edu.au>
Department of Pathology
Last modified: February 24, 2003