Fix fill in rotate (#1760)

* initial fix

* outsourced num bands lookup

* fix doc

* added pillow version requirement

* simplify number of bands extraction

* remove unrelated change

* remove indirect dependency on pillow>=5.2.0

* extend docstring to transform

* bug fix

* added test

test/test_transforms.py

 from __future__ import division
 import os
+import mock
 import torch
 import torchvision.transforms as transforms
 import torchvision.transforms.functional as F
@@ -1074,6 +1075,26 @@ class Tester(unittest.TestCase):
 
         self.assertTrue(np.all(np.array(result_a) == np.array(result_b)))
 
+    def test_rotate_fill(self):
+        img = F.to_pil_image(np.ones((100, 100, 3), dtype=np.uint8) * 255, "RGB")
+
+        modes = ("L", "RGB")
+        nums_bands = [len(mode) for mode in modes]
+        fill = 127
+
+        for mode, num_bands in zip(modes, nums_bands):
+            img_conv = img.convert(mode)
+            img_rot = F.rotate(img_conv, 45.0, fill=fill)
+            pixel = img_rot.getpixel((0, 0))
+
+            if not isinstance(pixel, tuple):
+                pixel = (pixel,)
+            self.assertTupleEqual(pixel, tuple([fill] * num_bands))
+
+            for wrong_num_bands in set(nums_bands) - {num_bands}:
+                with self.assertRaises(ValueError):
+                    F.rotate(img_conv, 45.0, fill=tuple([fill] * wrong_num_bands))
+
     def test_affine(self):
         input_img = np.zeros((40, 40, 3), dtype=np.uint8)
         pts = []

torchvision/transforms/functional.py

@@ -696,7 +696,7 @@ def adjust_gamma(img, gamma, gain=1):
     return img
 
 
-def rotate(img, angle, resample=False, expand=False, center=None, fill=0):
+def rotate(img, angle, resample=False, expand=False, center=None, fill=None):
     """Rotate the image by angle.
 
 
@@ -713,20 +713,39 @@ def rotate(img, angle, resample=False, expand=False, center=None, fill=0):
         center (2-tuple, optional): Optional center of rotation.
             Origin is the upper left corner.
             Default is the center of the image.
-        fill (3-tuple or int): RGB pixel fill value for area outside the rotated image.
-            If int, it is used for all channels respectively.
+        fill (n-tuple or int or float): Pixel fill value for area outside the rotated
+            image. If int or float, the value is used for all bands respectively.
+            Defaults to 0 for all bands. This option is only available for ``pillow>=5.2.0``.
 
     .. _filters: https://pillow.readthedocs.io/en/latest/handbook/concepts.html#filters
 
     """
+    def parse_fill(fill, num_bands):
+        if PILLOW_VERSION < "5.2.0":
+            if fill is None:
+                return {}
+            else:
+                msg = ("The option to fill background area of the rotated image, "
+                       "requires pillow>=5.2.0")
+                raise RuntimeError(msg)
+
+        if fill is None:
+            fill = 0
+        if isinstance(fill, (int, float)):
+            fill = tuple([fill] * num_bands)
+        if len(fill) != num_bands:
+            msg = ("The number of elements in 'fill' does not match the number of "
+                   "bands of the image ({} != {})")
+            raise ValueError(msg.format(len(fill), num_bands))
+
+        return {"fillcolor": fill}
 
     if not _is_pil_image(img):
         raise TypeError('img should be PIL Image. Got {}'.format(type(img)))
 
-    if isinstance(fill, int):
-        fill = tuple([fill] * 3)
+    opts = parse_fill(fill, len(img.getbands()))
 
-    return img.rotate(angle, resample, expand, center, fillcolor=fill)
+    return img.rotate(angle, resample, expand, center, **opts)
 
 
 def _get_inverse_affine_matrix(center, angle, translate, scale, shear):

torchvision/transforms/transforms.py

@@ -956,14 +956,15 @@ class RandomRotation(object):
         center (2-tuple, optional): Optional center of rotation.
             Origin is the upper left corner.
             Default is the center of the image.
-        fill (3-tuple or int): RGB pixel fill value for area outside the rotated image.
-            If int, it is used for all channels respectively.
+        fill (n-tuple or int or float): Pixel fill value for area outside the rotated
+            image. If int or float, the value is used for all bands respectively.
+            Defaults to 0 for all bands. This option is only available for ``pillow>=5.2.0``.
 
     .. _filters: https://pillow.readthedocs.io/en/latest/handbook/concepts.html#filters
 
     """
 
-    def __init__(self, degrees, resample=False, expand=False, center=None, fill=0):
+    def __init__(self, degrees, resample=False, expand=False, center=None, fill=None):
         if isinstance(degrees, numbers.Number):
             if degrees < 0:
                 raise ValueError("If degrees is a single number, it must be positive.")