add rotate transforms for image

chainercv/transforms/__init__.py

@@ -12,6 +12,7 @@
 from chainercv.transforms.image.random_sized_crop import random_sized_crop  # NOQA
 from chainercv.transforms.image.resize import resize  # NOQA
 from chainercv.transforms.image.resize_contain import resize_contain  # NOQA
+from chainercv.transforms.image.rotate import rotate  # NOQA
 from chainercv.transforms.image.scale import scale  # NOQA
 from chainercv.transforms.image.ten_crop import ten_crop  # NOQA
 from chainercv.transforms.point.flip_point import flip_point  # NOQA

chainercv/transforms/image/rotate.py

@@ -0,0 +1,41 @@
+import warnings
+
+
+try:
+    import scipy.ndimage
+    _available = True
+except ImportError:
+    _available = False
+
+
+def _check_available():
+    if not _available:
+        warnings.warn(
+            'SciPy is not installed in your environment,'
+            'so rotate cannot be loaded.'
+            'Please install SciPy to load dataset.\n\n'
+            '$ pip install scipy')
+
+
+def rotate(img, angle, expand=True):
+    """Rotate images by degrees.
+
+    Args:
+        img (~numpy.ndarray): An arrays that get rotated. This is in
+            CHW format.
+        angle (float): Counter clock-wise rotation angle (degree) in
+            [-180, 180].
+        expand (bool): The output shaped is adapted or not.
+            If :obj:`True`, the input image is contained complete in
+            the output.
+
+    Returns:
+        ~numpy.ndarray:
+        returns an array :obj:`out_img` that is the result of rotation.
+
+    """
+
+    _check_available()
+
+    assert 180 >= angle >= -180
+    return scipy.ndimage.rotate(img, angle, axes=(2, 1), reshape=expand)

docs/source/reference/transforms.rst

@@ -47,6 +47,10 @@ resize_contain
 ~~~~~~~~~~~~~~
 .. autofunction:: resize_contain
 
+rotate
+~~~~~~
+.. autofunction:: rotate
+
 scale
 ~~~~~
 .. autofunction:: scale

tests/transforms_tests/image_tests/test_rotate.py

@@ -0,0 +1,32 @@
+import random
+import unittest
+
+import numpy as np
+
+from chainer import testing
+from chainercv.transforms import flip
+from chainercv.transforms import rotate
+
+try:
+    import scipy  # NOQA
+    _available = True
+except ImportError:
+    _available = False
+
+
+@unittest.skipUnless(_available, 'SciPy is not installed')
+class TestRotate(unittest.TestCase):
+
+    def test_rotate(self):
+        img = np.random.uniform(size=(3, 32, 24))
+        angle = random.uniform(0, 180)
+
+        out = rotate(img, angle)
+        expected = flip(img, x_flip=True)
+        expected = rotate(expected, -1 * angle)
+        expected = flip(expected, x_flip=True)
+
+        np.testing.assert_almost_equal(out, expected, decimal=6)
+
+
+testing.run_module(__name__, __file__)