Default to using Pytorch APIs for `monai.transforms` (ETA TBD)

[wyli]

Is your feature request related to a problem? Please describe.
Based on our discussions, this ticket proposes to implement the MONAI transforms preferably using the Pytorch APIs instead of the current mainly numpy-based solutions.

[wyli]

as an initial step, the transform should support both tensor and ndarray types, and return value should have the same type as input.

[rijobro]

I had a thought about this. LoadImage would still return numpy and therefore all transforms that follow would be doing numpy<->torch conversions. So, to make the most of this suggested plan of returning the image in the same type as the input, we would want to move the ToTensor as early as possible, e.g.:

t = Compose([
    LoadImage,
    ToTensor,
    AllOtherTransforms,
    ...
])

Alternatively, we modify LoadImage to return torch.Tensor, but this would be a breaking change.

[wyli]

because this is a significant feature, how about we create a feature branch for it in the codebase? when it's entirely ready we merge it into dev. otherwise we keep the feature branch up-to-date with the dev branch. all of us can collaborate on the feature branch.

[rijobro]

If I do this as a branch on the Project-MONAI fork, will I have to get an approved code review every time I want to commit? If so, I think I'll just do it as a branch on my fork.

[wyli]

that's also fine, just two thoughts:

• from your fork , you wouldn't be able to trigger the full self-hosted ci pipelines (I feel we may need a full test before merging)
• we (at least @Nic-Ma and I) could help build this feature together, submitting PRs to a MONAI branch is easier than submitting them to your fork...

[rijobro]

Ok. Could we create a branch that has CI/CD testing, but doesn't require code reviews? Potentially also doesn't require the tests to pass before pushing to that particular branch (just to speed things up, we'd have to be careful not to break things of course).

[wyli]

sounds great, we should do the same for any major new features in the future...

[rijobro]

Great. I can't create branches on the main repository, could you take care of that?

[wyli]

sure, created feature/2231-transforms (https://github.com/Project-MONAI/MONAI/tree/feature/2231-transforms) I'll push update ci/cd config to include this feature/* pattern