[fbsync] Adding Scale Jitter transform for detection (#5435)

Summary:
* Adding Scale Jitter in references.

* Update documentation.

* Address review comments.

Reviewed By: jdsgomes

Differential Revision: D34475308

fbshipit-source-id: dcdb00685d4de39b7315ff7d4b9cfb2411218e5c

references/detection/transforms.py

@@ -4,7 +4,7 @@
 import torchvision
 from torch import nn, Tensor
 from torchvision.transforms import functional as F
-from torchvision.transforms import transforms as T
+from torchvision.transforms import transforms as T, InterpolationMode
 
 
 def _flip_coco_person_keypoints(kps, width):
@@ -282,3 +282,52 @@ def forward(
                 image = F.to_pil_image(image)
 
         return image, target
+
+
+class ScaleJitter(nn.Module):
+    """Randomly resizes the image and its bounding boxes  within the specified scale range.
+    The class implements the Scale Jitter augmentation as described in the paper
+    `"Simple Copy-Paste is a Strong Data Augmentation Method for Instance Segmentation" <https://arxiv.org/abs/2012.07177>`_.
+
+    Args:
+        target_size (tuple of ints): The target size for the transform provided in (height, weight) format.
+        scale_range (tuple of ints): scaling factor interval, e.g (a, b), then scale is randomly sampled from the
+            range a <= scale <= b.
+        interpolation (InterpolationMode): Desired interpolation enum defined by
+            :class:`torchvision.transforms.InterpolationMode`. Default is ``InterpolationMode.BILINEAR``.
+    """
+
+    def __init__(
+        self,
+        target_size: Tuple[int, int],
+        scale_range: Tuple[float, float] = (0.1, 2.0),
+        interpolation: InterpolationMode = InterpolationMode.BILINEAR,
+    ):
+        super().__init__()
+        self.target_size = target_size
+        self.scale_range = scale_range
+        self.interpolation = interpolation
+
+    def forward(
+        self, image: Tensor, target: Optional[Dict[str, Tensor]] = None
+    ) -> Tuple[Tensor, Optional[Dict[str, Tensor]]]:
+        if isinstance(image, torch.Tensor):
+            if image.ndimension() not in {2, 3}:
+                raise ValueError(f"image should be 2/3 dimensional. Got {image.ndimension()} dimensions.")
+            elif image.ndimension() == 2:
+                image = image.unsqueeze(0)
+
+        r = self.scale_range[0] + torch.rand(1) * (self.scale_range[1] - self.scale_range[0])
+        new_width = int(self.target_size[1] * r)
+        new_height = int(self.target_size[0] * r)
+
+        image = F.resize(image, [new_height, new_width], interpolation=self.interpolation)
+
+        if target is not None:
+            target["boxes"] *= r
+            if "masks" in target:
+                target["masks"] = F.resize(
+                    target["masks"], [new_height, new_width], interpolation=InterpolationMode.NEAREST
+                )
+
+        return image, target