no itk.join_image_filter in ITK 5.1.2

[matt.mccormick]

@dyoll

However, the API of image_view_from_array and image_from_array doesn’t seem to allow to specify the pixel type explicitly.

ITK 5.2, whose release candidate is coming up, has more support for vector pixel types in these functions and in an image.astype function.

@dyoll

I am trying to join components of a tensor image (stored as scalar images) and thought it a good task to start using the python interface instead of c++.

While we can add more wrapping for join_image_filter, but combining scalar images into a multi-component image is already supported with itk.compose_image_filter. For example,

arrays = [component1, component2, component3]
together = itk.compose_image_filter(*arrays)

# or
images = [itk.image_view_from_array(a) for a in arrays]
together = itk.compose_image_filter(*images)