Allow controlling intensity of RandomMotion transform

🚀 Feature

Motivation

Intensity of RandomMotion transform seems to mostly depend on the “time” of the motion. And while RandomGhosting transform exposes intensity parameter, RandomMotion does not expose times parameter, and does not have intensity.

Pitch

Either provide intensity parameter, or allow setting the range of times parameter used internally.

Alternatives

Save the image before the transform is applied, then “manually” blend the transformed one into the original one with custom weight, thus emulating intensity.

Additional context

I am trying to augment training by creating bad images for an image quality estimator, because most images in my training set are good. I would like to control the degree of corruption, e.g. to have control whether I produce an image with rating of 1/10 or 4/10.

[fepegar]

I coded this transform a long time ago reading Richard Shaw’s paper. My version is a bit simplified, but works. I am now away at a conference, but I’ll try to add some explanations to the docs when I’m back.

For now, maybe you can just use a convex combination of the original image and the transformed one:

import torch
import torchio as tio


class MyRandomMotion(tio.RandomMotion):
    def __init__(self, *, intensity, **kwargs):
        self.intensity = intensity
        super().__init__(**kwargs)

    def apply_transform(self, subject):
        transformed = super().apply_transform(subject)
        for image_name in self.get_images_dict(subject):
            original = subject[image_name]
            new = transformed[image_name]
            alpha = self.intensity
            composite_data = new.data * alpha + original.data * (1 - alpha)
            transformed[image_name].set_data(composite_data)
        return transformed


fpg = tio.datasets.FPG()
seed = 42

transform = MyRandomMotion(intensity=0)
torch.manual_seed(seed)
transform(fpg).t1.plot()

transform = MyRandomMotion(intensity=1)
torch.manual_seed(seed)
transform(fpg).t1.plot()

[fepegar]

@fepegar would it be easy to add Motion transform in the Slicer pluggin ? (this would answer the initial need of exploration) and more generally it may be interesting for other transform too (ie not the Radom version)

It would be easy, yes. But it would take a bit of time, which I don’t really have now. Feel free to open a PR!