Add shear parallel to y-axis (#1070)

* initial commit

* add more checks, fix lint, fix doc

test/test_transforms.py

@@ -1087,15 +1087,15 @@ class Tester(unittest.TestCase):
 
         def _test_transformation(a, t, s, sh):
             a_rad = math.radians(a)
-            s_rad = math.radians(sh)
+            s_rad = [math.radians(sh_) for sh_ in sh]
             # 1) Check transformation matrix:
             c_matrix = np.array([[1.0, 0.0, cnt[0]], [0.0, 1.0, cnt[1]], [0.0, 0.0, 1.0]])
             c_inv_matrix = np.linalg.inv(c_matrix)
             t_matrix = np.array([[1.0, 0.0, t[0]],
                                  [0.0, 1.0, t[1]],
                                  [0.0, 0.0, 1.0]])
-            r_matrix = np.array([[s * math.cos(a_rad), -s * math.sin(a_rad + s_rad), 0.0],
-                                 [s * math.sin(a_rad), s * math.cos(a_rad + s_rad), 0.0],
+            r_matrix = np.array([[s * math.cos(a_rad + s_rad[1]), -s * math.sin(a_rad + s_rad[0]), 0.0],
+                                 [s * math.sin(a_rad + s_rad[1]), s * math.cos(a_rad + s_rad[0]), 0.0],
                                  [0.0, 0.0, 1.0]])
             true_matrix = np.dot(t_matrix, np.dot(c_matrix, np.dot(r_matrix, c_inv_matrix)))
             result_matrix = _to_3x3_inv(F._get_inverse_affine_matrix(center=cnt, angle=a,
@@ -1124,18 +1124,18 @@ class Tester(unittest.TestCase):
 
         # Test rotation
         a = 45
-        _test_transformation(a=a, t=(0, 0), s=1.0, sh=0.0)
+        _test_transformation(a=a, t=(0, 0), s=1.0, sh=(0.0, 0.0))
 
         # Test translation
         t = [10, 15]
-        _test_transformation(a=0.0, t=t, s=1.0, sh=0.0)
+        _test_transformation(a=0.0, t=t, s=1.0, sh=(0.0, 0.0))
 
         # Test scale
         s = 1.2
-        _test_transformation(a=0.0, t=(0.0, 0.0), s=s, sh=0.0)
+        _test_transformation(a=0.0, t=(0.0, 0.0), s=s, sh=(0.0, 0.0))
 
         # Test shear
-        sh = 45.0
+        sh = [45.0, 25.0]
         _test_transformation(a=0.0, t=(0.0, 0.0), s=1.0, sh=sh)
 
         # Test rotation, scale, translation, shear
@@ -1143,7 +1143,7 @@ class Tester(unittest.TestCase):
             for t1 in range(-10, 10, 5):
                 for s in [0.75, 0.98, 1.0, 1.1, 1.2]:
                     for sh in range(-15, 15, 5):
-                        _test_transformation(a=a, t=(t1, t1), s=s, sh=sh)
+                        _test_transformation(a=a, t=(t1, t1), s=s, sh=(sh, sh))
 
     def test_random_rotation(self):
 
@@ -1182,11 +1182,12 @@ class Tester(unittest.TestCase):
             transforms.RandomAffine([-90, 90], translate=[0.2, 0.2], scale=[0.5, 0.5], shear=-7)
             transforms.RandomAffine([-90, 90], translate=[0.2, 0.2], scale=[0.5, 0.5], shear=[-10])
             transforms.RandomAffine([-90, 90], translate=[0.2, 0.2], scale=[0.5, 0.5], shear=[-10, 0, 10])
+            transforms.RandomAffine([-90, 90], translate=[0.2, 0.2], scale=[0.5, 0.5], shear=[-10, 0, 10, 0, 10])
 
         x = np.zeros((100, 100, 3), dtype=np.uint8)
         img = F.to_pil_image(x)
 
-        t = transforms.RandomAffine(10, translate=[0.5, 0.3], scale=[0.7, 1.3], shear=[-10, 10])
+        t = transforms.RandomAffine(10, translate=[0.5, 0.3], scale=[0.7, 1.3], shear=[-10, 10, 20, 40])
         for _ in range(100):
             angle, translations, scale, shear = t.get_params(t.degrees, t.translate, t.scale, t.shear,
                                                              img_size=img.size)
@@ -1196,7 +1197,8 @@ class Tester(unittest.TestCase):
             assert -img.size[1] * 0.5 <= translations[1] <= img.size[1] * 0.5, \
                 "{} vs {}".format(translations[1], img.size[1] * 0.5)
             assert 0.7 < scale < 1.3
-            assert -10 < shear < 10
+            assert -10 < shear[0] < 10
+            assert -20 < shear[1] < 40
 
         # Checking if RandomAffine can be printed as string
         t.__repr__()

torchvision/transforms/functional.py

@@ -722,20 +722,29 @@ def _get_inverse_affine_matrix(center, angle, translate, scale, shear):
     # where T is translation matrix: [1, 0, tx | 0, 1, ty | 0, 0, 1]
     #       C is translation matrix to keep center: [1, 0, cx | 0, 1, cy | 0, 0, 1]
     #       RSS is rotation with scale and shear matrix
-    #       RSS(a, scale, shear) = [ cos(a)*scale    -sin(a + shear)*scale     0]
-    #                              [ sin(a)*scale    cos(a + shear)*scale     0]
+    #       RSS(a, scale, shear) = [ cos(a + shear_y)*scale    -sin(a + shear_x)*scale     0]
+    #                              [ sin(a + shear_y)*scale    cos(a + shear_x)*scale     0]
     #                              [     0                  0          1]
     # Thus, the inverse is M^-1 = C * RSS^-1 * C^-1 * T^-1
 
     angle = math.radians(angle)
+    if isinstance(shear, (tuple, list)) and len(shear) == 2:
+        shear = [math.radians(s) for s in shear]
+    elif isinstance(shear, numbers.Number):
         shear = math.radians(shear)
+        shear = [shear, 0]
+    else:
+        raise ValueError(
+            "Shear should be a single value or a tuple/list containing " +
+            "two values. Got {}".format(shear))
     scale = 1.0 / scale
 
     # Inverted rotation matrix with scale and shear
-    d = math.cos(angle + shear) * math.cos(angle) + math.sin(angle + shear) * math.sin(angle)
+    d = math.cos(angle + shear[0]) * math.cos(angle + shear[1]) + \
+        math.sin(angle + shear[0]) * math.sin(angle + shear[1])
     matrix = [
-        math.cos(angle + shear), math.sin(angle + shear), 0,
-        -math.sin(angle), math.cos(angle), 0
+        math.cos(angle + shear[0]), math.sin(angle + shear[0]), 0,
+        -math.sin(angle + shear[1]), math.cos(angle + shear[1]), 0
     ]
     matrix = [scale / d * m for m in matrix]
 
@@ -757,7 +766,9 @@ def affine(img, angle, translate, scale, shear, resample=0, fillcolor=None):
         angle (float or int): rotation angle in degrees between -180 and 180, clockwise direction.
         translate (list or tuple of integers): horizontal and vertical translations (post-rotation translation)
         scale (float): overall scale
-        shear (float): shear angle value in degrees between -180 to 180, clockwise direction.
+        shear (float or tuple or list): shear angle value in degrees between -180 to 180, clockwise direction.
+        If a tuple of list is specified, the first value corresponds to a shear parallel to the x axis, while
+        the second value corresponds to a shear parallel to the y axis.
         resample (``PIL.Image.NEAREST`` or ``PIL.Image.BILINEAR`` or ``PIL.Image.BICUBIC``, optional):
             An optional resampling filter.
             See `filters`_ for more information.

torchvision/transforms/transforms.py

@@ -1013,8 +1013,11 @@ class RandomAffine(object):
         scale (tuple, optional): scaling factor interval, e.g (a, b), then scale is
             randomly sampled from the range a <= scale <= b. Will keep original scale by default.
         shear (sequence or float or int, optional): Range of degrees to select from.
-            If degrees is a number instead of sequence like (min, max), the range of degrees
-            will be (-degrees, +degrees). Will not apply shear by default
+            If shear is a number, a shear parallel to the x axis in the range (-shear, +shear)
+            will be apllied. Else if shear is a tuple or list of 2 values a shear parallel to the x axis in the
+            range (shear[0], shear[1]) will be applied. Else if shear is a tuple or list of 4 values,
+            a x-axis shear in (shear[0], shear[1]) and y-axis shear in (shear[2], shear[3]) will be applied.
+            Will not apply shear by default
         resample ({PIL.Image.NEAREST, PIL.Image.BILINEAR, PIL.Image.BICUBIC}, optional):
             An optional resampling filter. See `filters`_ for more information.
             If omitted, or if the image has mode "1" or "P", it is set to PIL.Image.NEAREST.
@@ -1057,9 +1060,14 @@ class RandomAffine(object):
                     raise ValueError("If shear is a single number, it must be positive.")
                 self.shear = (-shear, shear)
             else:
-                assert isinstance(shear, (tuple, list)) and len(shear) == 2, \
-                    "shear should be a list or tuple and it must be of length 2."
-                self.shear = shear
+                assert isinstance(shear, (tuple, list)) and \
+                    (len(shear) == 2 or len(shear) == 4), \
+                    "shear should be a list or tuple and it must be of length 2 or 4."
+                # X-Axis shear with [min, max]
+                if len(shear) == 2:
+                    self.shear = [shear[0], shear[1], 0., 0.]
+                elif len(shear) == 4:
+                    self.shear = [s for s in shear]
         else:
             self.shear = shear
 
@@ -1088,7 +1096,11 @@ class RandomAffine(object):
             scale = 1.0
 
         if shears is not None:
-            shear = random.uniform(shears[0], shears[1])
+            if len(shears) == 2:
+                shear = [random.uniform(shears[0], shears[1]), 0.]
+            elif len(shears) == 4:
+                shear = [random.uniform(shears[0], shears[1]),
+                         random.uniform(shears[2], shears[3])]
         else:
             shear = 0.0