[Neuroimaging] flipping left-right side of images

[Christophe Pallier]

Dear all ,

I am trying to flip maks images which are in MNI space.
I have tried the  naive approach of flipping the data array in voxel
space, but the results is not satisfactory (the result is not
symmetrical to the original)

---
from numpy import flip

img = nib.load('mask.nii')
data = img.get_data()
nib.save(nib.Nifti1Image(np.flip(data, axis=0),  affine=img.affine), 'test.nii')
---

I also tried to hack the affine matrix, switching the sign of the
first element, and using nilearn.image.resample_img, to create a new
image, but with bad result.

Any suggestion?