The Affine transform currently does not have an affine matrix parameter

Is your feature request related to a problem? Please describe. The Affine transform forwards its parameters to the AffineGrid class. But it currently does not provide the “affine” parameter which the AffineGrid class also has.

This allows to directly define a affine transformation matrix instead of individual parameters for transformations like rotation. If computations are directly done with affine transformation matrices, this parameter is really helpful (necessary).

Describe the solution you’d like The only change necessary, is to add the affine parameter and to forward it to the AffineGrid class.

class Affine(Transform):
    ...
    def __init__(
        ...
        affine: Optional[NdarrayOrTensor] = None,
        ...
    ) -> None:
        ...
        self.affine_grid = AffineGrid(
            ...
            affine=affine,
            ...
        )

Describe alternatives you’ve considered We patched the affine transform locally.

[Nic-Ma]

Hi @Spenhouet ,

Thanks for your feedback. @wyli @ericspod I think this feature request can help improve the user experience, if you guys don’t have other concerns, I will try to add it based on the suggestion here.

Thanks in advance.

[Spenhouet]

@wyli Maybe I misunderstood. We are not using the method to apply a static Affine in the pipeline. We are in fact using it like mentioned above.

I get where you are coming from, but I wonder if this is the right case to focus on this. The if-else branches already exist. The suggestion simply exposes the affine parameter to the Affine transform to not need to implement it like you suggested.

I don’t think it will make the Affine transform any more complicated.

EDIT: But it will make other methods which use this Affine transform simpler. So we save on complexity there.

EDIT2: Or how would you rate the code complexity on these two code snippets:

transform = Affine(affine=projection[:3, :3], mode=self.mode)
transformed_matrix, _ = transform(img.squeeze(0)) 

vs.

transform = Affine(mode=self.mode)
transformed_matrix = transform.resampler(img.squeeze(0), transform.affinegrid(projection[:3, :3])[0])

EDIT3: Also the first one will also output the resulting affine while the second will not and will need additional code (further increasing code complexity and boilerplate).