Fix the order of return values for hessian_matrix
#6624
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For mode='rc' the 2nd derivative along axis=0 should come first. This change also makes the order consistent with that used by structure_tensor
add test cases to confirm expected behavior for order
This was referenced Nov 20, 2022
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CI failures are unrelated and fixed by #6626 |
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@lagru Want to make the minor adjustment to the test and merge this? |
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Okay, I'll take your #6624 (comment) as an approval. |
Explanation: Each array in Hs is the result of
H_elems = [np.gradient(gradients[ax0], axis=ax1)
for ax0, ax1 in combinations_with_replacement(axes, 2)]
Because reversing axes (due to the bug fix) doesn't affect the result
of `H_elems[2]`. For index 2, `combinations_with_replacement(axes, 2)`
returns either `(0, 2)` or the reversed `(2, 0)`. Both result in the
same gradient.
So to make the test notice this change, we test another one of H_elems
arrays whose result is not the same if axes is reversed.
This was referenced Feb 24, 2023
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closes #5230
This fixes the reported bug where 'xy' order was returned when 'rc' was requested and vice-versa. The change here also matrix
hessian_matrixorder consistent withstructure_tensorwhich has the same conventions.A second inconsistency is that
structure_tensoronly allows use of mode='xy' for 2D images and otherwise raises an error, whilehessian_matrixdid not have this restriction. I have changed thehessian_matrixbehavior here for consistency.Fortunately, the presence of this bug did not effect the use cases of this function in higher order functions within scikit-image (e.g.
blob_dohand various ridge filters likesato,meijering,frangi). The eigenvalues used by the ridge filters, for example, are the same whether or not the axes are reversed.