add rotate_bbox

chainercv/transforms/__init__.py

@@ -1,6 +1,7 @@
 from chainercv.transforms.bbox.crop_bbox import crop_bbox  # NOQA
 from chainercv.transforms.bbox.flip_bbox import flip_bbox  # NOQA
 from chainercv.transforms.bbox.resize_bbox import resize_bbox  # NOQA
+from chainercv.transforms.bbox.rotate_bbox import rotate_bbox  # NOQA
 from chainercv.transforms.bbox.translate_bbox import translate_bbox  # NOQA
 from chainercv.transforms.image.center_crop import center_crop  # NOQA
 from chainercv.transforms.image.flip import flip  # NOQA

chainercv/transforms/bbox/rotate_bbox.py

@@ -0,0 +1,43 @@
+import numpy as np
+
+
+def rotate_bbox(bbox, angle, size):
+    """Rotate bounding boxes by degrees.
+
+    Args:
+        bbox (~numpy.ndarray): An array whose shape is :math:`(R, 4)`.
+            :math:`R` is the number of bounding boxes.
+        angle (float): Counter clock-wise rotation angle (degree) in
+            [-180, 180].
+            image is rotated by 90 degrees.
+        size (tuple): A tuple of length 2. The height and the width
+            of the image.
+
+    Returns:
+        ~numpy.ndarray:
+        Bounding boxes rescaled according to the given :obj:`k`.
+
+    """
+    if angle % 90 != 0:
+        raise ValueError(
+            'angle in [180, 90, 0, -90, -180] is only supported: {}'
+            .format(angle))
+        return bbox
+    H, W = size
+    if angle == 0:
+        return bbox
+
+    if angle == 90:
+        rotated_bbox = np.concatenate(
+            (W - bbox[:, 3:4], bbox[:, 0:1],
+             W - bbox[:, 1:2], bbox[:, 2:3]), axis=1)
+    elif angle in [180, -180]:
+        rotated_bbox = np.concatenate(
+            (H - bbox[:, 2:3], W - bbox[:, 3:4],
+             H - bbox[:, 0:1], W - bbox[:, 1:2]), axis=1)
+    elif angle == -90:
+        rotated_bbox = np.concatenate(
+            (bbox[:, 1:2], H - bbox[:, 2:3],
+             bbox[:, 3:4], H - bbox[:, 0:1]), axis=1)
+    rotated_bbox = rotated_bbox.astype(bbox.dtype)
+    return rotated_bbox

docs/source/reference/transforms.rst

@@ -71,6 +71,10 @@ resize_bbox
 ~~~~~~~~~~~
 .. autofunction:: resize_bbox
 
+rotate_bbox
+~~~~~~~~~~~
+.. autofunction:: rotate_bbox
+
 translate_bbox
 ~~~~~~~~~~~~~~
 .. autofunction:: translate_bbox

tests/transforms_tests/bbox_tests/test_rotate_bbox.py

@@ -0,0 +1,29 @@
+import unittest
+
+import numpy as np
+
+from chainer import testing
+from chainercv.transforms import rotate_bbox
+from chainercv.utils import generate_random_bbox
+
+
+@testing.parameterize(*testing.product({
+    'angle': [180, 90, 0, -90, -180]
+}))
+class TestRotateBbox(unittest.TestCase):
+
+    def test_rotate_bbox(self):
+        size = (32, 24)
+        bbox = generate_random_bbox(10, size, 0, 24)
+
+        out = rotate_bbox(bbox, self.angle, size)
+        if self.angle % 180 != 0:
+            rotate_size = size[::-1]
+        else:
+            rotate_size = size
+        out = rotate_bbox(out, -1 * self.angle, rotate_size)
+
+        np.testing.assert_almost_equal(out, bbox, decimal=6)
+
+
+testing.run_module(__name__, __file__)