ITKReader doesn't return numpy array

Describe the bug Currently, we use the itk.array_view_from_image() to get data array: https://github.com/Project-MONAI/MONAI/blob/dev/monai/data/image_reader.py#L316 But actually, it’s not numpy array, so following logic which depends on numpy.ndarray type will fail.

loader = LoadImage()
img, meta = loader(dicom_path)
print(type(img))

Get the output:

<class 'itk.itkPyBufferPython.NDArrayITKBase'>

[Nic-Ma]

Hi @wyli ,

After some testing, I feel it’s better to also update ITK reader to use np.asarray(), because some operations of NDArrayITKBase is different from ndarray, very easy to cause unknown errors. For example:

print(type(img))
ret = np.mean(img)
print(isinstance(ret, np.ndarray))
print(ret)

img1 = np.array([1, 2, 3])
print(type(img1))
ret1 = np.mean(img1)
print(isinstance(ret1, np.ndarray))
print(ret1)

The output is:

<class 'itk.itkPyBufferPython.NDArrayITKBase'>
True
-3.4086406e-07
<class 'numpy.ndarray'>
False
2.0

The check for isinstance(mean, np.ndarray) will fail here.

What do you think?

Thanks.

[wyli]

NDArrayITKBase is a subclass of ndarray, shouldn’t we enhance/fix the relevant failing logic instead of converting them to ndarray, is this a duplicate ticket of #2885?