[SciPy-User] mappping argument in scipy.ndimage.interpolation.geometric_transform

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[SciPy-User] mappping argument in scipy.ndimage.interpolation.geometric_transform

EV Petr

Hi all,

A few days ago I worked on the Moebius transformation of an image for a course in Complex Analysis: http://nbviewer.jupyter.org/github/empet/Math/blob/master/Moebius-transform-image.ipynb
I’m mathematician and had no previous knowledge in image processing. Reading a few references across the web I succeeded to understand
how the scipy.ndimage.interpolation.geometric_transform works.

Discussing with a colleague who had the book Learning SciPy for Numerical and Scientific Computing - Second Edition https://www.safaribooksonline.com/library/view/learning-scipy-for/9781783987702/ he told me that my implementation differ from that in this book (see here a snippet showing the authors code: https://github.com/empet/Math/blob/master/Imags/Scipy-extract-book.PNG)
I realized that the authors of the book did not know that geometric_transform implements the backward method, and instead of the inverse Moebius transform they passed the transform itself to geometric_transform function. I left a message on one of the authors github page, pointing out this issue, but it appears that he doesn’t agree with me (in fact he doesn’t understand the key point of the filled issue: https://github.com/rojassergio/Learning-Scipy/issues/1#issuecomment-257555364).
That is why I ask people on this forum, who are more skilled than we are, to express their opinion. On friday I will illustrate for a group of student how the Moebius transform works and want to know whether my implementation is correct.
Thanks,

EP



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