The rotational image difference function (rotIDF) as a quantitative measure of the navigational information content of natural scenes.

<p>(<b>A</b>) Two functions for the two scenes at the bottom show the r.m.s. pixel differences at different steps of rotation of each image against itself. Note differences in the depth (d) and the radius (r) of the functions and how both depend on the spatial frequency content of scenes. (<b>B</b>) The difference in rotIDF depth between different scenes is maintained after local contrast normalization. (see [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196227#pone.0196227.ref004" target="_blank">4</a>] for a quantitative analysis).