box_rescale function to rescale bounding boxes to a new image shape

docs/source/ops.rst

@@ -13,6 +13,7 @@ torchvision.ops
 .. autofunction:: batched_nms
 .. autofunction:: remove_small_boxes
 .. autofunction:: clip_boxes_to_image
+.. autofunction:: box_rescale
 .. autofunction:: box_convert
 .. autofunction:: box_area
 .. autofunction:: box_iou

torchvision/ops/boxes.py

@@ -154,6 +154,24 @@ def clip_boxes_to_image(boxes: Tensor, size: Tuple[int, int]) -> Tensor:
     return clipped_boxes.reshape(boxes.shape)
 
 
+def box_rescale(boxes: Tensor, in_shape: Tuple[int, int], out_shape: Tuple[int, int]) -> Tensor:
+    """
+    Rescale boxes to a new image shape.
+
+    Args:
+        boxes: (Tensor[N, 4]): boxes to rescale, in ``(x1, y1, x2, y2)`` format.
+        in_shape: (Tuple[int, int]): current shape of the image.
+        out_shape: (Tuple[int, int]): desired shape of the image.
+
+    Returns:
+        Tensor[N, 4]: rescaled boxes
+    """
+    rescaled = boxes.new(boxes.shape)
+    rescaled[:, 0::2] = boxes[:, 0::2] * (out_shape[1] / in_shape[1])
+    rescaled[:, 1::2] = boxes[:, 1::2] * (out_shape[0] / in_shape[0])
+    return rescaled
+
+
 def box_convert(boxes: Tensor, in_fmt: str, out_fmt: str) -> Tensor:
     """
     Converts boxes from given in_fmt to out_fmt.