MattesMutualInformation corner case spacing error

[michaelzenkay]

Description

corner case error in ITK's MattesMutualInformation metric when both images are all zeros, then the internal data structure (Image) has the reported invalid size

Steps to Reproduce

import SimpleITK as sitk
import numpy as np

I = np.zeros((100,100,100))
I = sitk.GetImageFromArray(I)
I.SetSpacing((1.0,1.0,1.0))
I = sitk.Cast(I, sitk.sitkFloat32)

J = np.zeros((100,100,100))
J = sitk.GetImageFromArray(J)
J.SetSpacing((1.0,1.0,1.0))
J = sitk.Cast(J, sitk.sitkFloat32)

R = sitk.ImageRegistrationMethod()
R.SetMetricAsMattesMutualInformation()
MMI = R.MetricEvaluate(I, J)

Expected behavior

Evaluation of Mutual Information Metric

Actual behavior

ERROR: Image(0x32256f0): A spacing of 0 is not allowed: Spacing is [0, 0]

Reproducibility

100%

Versions

Environment

Ubuntu 18.04, python 3.7, SimpleITK 1.1.0, numpy 1.17.2

Additional Information

Changing metric e.g. SetMetricAsCorrelation() does not throw error -> therefore must be the MattesMutualInformation metric
Initializing image with np.random.rand(100,100,100) does not throw error -> therefore must be the corner case where inputs are zero

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.