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To invert a piecewise affine transform, you'll have to use SciPy KD-tree to find the nearest quad coordinates, and then invert the matching affine.  This is not necessarily hard, but it's not trivial to implement.  Definitely too hard for a beginner :-) Probably I should just increase image canvas size to have empty area cropped and the picture to remain full. Thanks. Best regards, Serge Shakhov.

On Friday, 7 April 2017, 4:57, Stefan van der Walt <stefanv@berkeley.edu> wrote: On Wed, Apr 5, 2017, at 19:02, Serge Shakhov wrote:  Just want to clarify. Am I right that your solution isn't applicable to PiecewiseAffineTransform at all? Do you think it may be possible to find a workaround? Sorry, I should have been clearer.  With "defined" I meant implemented. To invert a piecewise affine transform, you'll have to use SciPy KD-tree to find the nearest quad coordinates, and then invert the matching affine.  This is not necessarily hard, but it's not trivial to implement. Stéfan