[Feature] Add diagonal flip (#515)

mmcv/image/geometric.py

@@ -187,16 +187,19 @@ def imflip(img, direction='horizontal'):
 
     Args:
         img (ndarray): Image to be flipped.
-        direction (str): The flip direction, either "horizontal" or "vertical".
+        direction (str): The flip direction, either "horizontal" or
+            "vertical" or "diagonal".
 
     Returns:
         ndarray: The flipped image.
     """
-    assert direction in ['horizontal', 'vertical']
+    assert direction in ['horizontal', 'vertical', 'diagonal']
     if direction == 'horizontal':
         return np.flip(img, axis=1)
-    else:
+    elif direction == 'vertical':
         return np.flip(img, axis=0)
+    else:
+        return np.flip(img, axis=(0, 1))
 
 
 def imflip_(img, direction='horizontal'):
@@ -204,16 +207,19 @@ def imflip_(img, direction='horizontal'):
 
     Args:
         img (ndarray): Image to be flipped.
-        direction (str): The flip direction, either "horizontal" or "vertical".
+        direction (str): The flip direction, either "horizontal" or
+            "vertical" or "diagonal".
 
     Returns:
         ndarray: The flipped image (inplace).
     """
-    assert direction in ['horizontal', 'vertical']
+    assert direction in ['horizontal', 'vertical', 'diagonal']
     if direction == 'horizontal':
         return cv2.flip(img, 1, img)
-    else:
+    elif direction == 'vertical':
         return cv2.flip(img, 0, img)
+    else:
+        return cv2.flip(img, -1, img)
 
 
 def imrotate(img,

tests/test_image/test_geometric.py

@@ -108,6 +108,10 @@ class TestGeometric:
             mmcv.imrescale(self.img, [100, 100])
 
     def test_imflip(self):
+        # direction must be "horizontal" or "vertical" or "diagonal"
+        with pytest.raises(AssertionError):
+            mmcv.imflip(np.random.rand(80, 60, 3), direction='random')
+
         # test horizontal flip (color image)
         img = np.random.rand(80, 60, 3)
         h, w, c = img.shape
@@ -117,6 +121,7 @@ class TestGeometric:
             for j in range(w):
                 for k in range(c):
                     assert flipped_img[i, j, k] == img[i, w - 1 - j, k]
+
         # test vertical flip (color image)
         flipped_img = mmcv.imflip(img, direction='vertical')
         assert flipped_img.shape == img.shape
@@ -124,6 +129,15 @@ class TestGeometric:
             for j in range(w):
                 for k in range(c):
                     assert flipped_img[i, j, k] == img[h - 1 - i, j, k]
+
+        # test diagonal flip (color image)
+        flipped_img = mmcv.imflip(img, direction='diagonal')
+        assert flipped_img.shape == img.shape
+        for i in range(h):
+            for j in range(w):
+                for k in range(c):
+                    assert flipped_img[i, j, k] == img[h - 1 - i, w - 1 - j, k]
+
         # test horizontal flip (grayscale image)
         img = np.random.rand(80, 60)
         h, w = img.shape
@@ -132,6 +146,7 @@ class TestGeometric:
         for i in range(h):
             for j in range(w):
                 assert flipped_img[i, j] == img[i, w - 1 - j]
+
         # test vertical flip (grayscale image)
         flipped_img = mmcv.imflip(img, direction='vertical')
         assert flipped_img.shape == img.shape
@@ -139,7 +154,18 @@ class TestGeometric:
             for j in range(w):
                 assert flipped_img[i, j] == img[h - 1 - i, j]
 
+        # test diagonal flip (grayscale image)
+        flipped_img = mmcv.imflip(img, direction='diagonal')
+        assert flipped_img.shape == img.shape
+        for i in range(h):
+            for j in range(w):
+                assert flipped_img[i, j] == img[h - 1 - i, w - 1 - j]
+
     def test_imflip_(self):
+        # direction must be "horizontal" or "vertical" or "diagonal"
+        with pytest.raises(AssertionError):
+            mmcv.imflip_(np.random.rand(80, 60, 3), direction='random')
+
         # test horizontal flip (color image)
         img = np.random.rand(80, 60, 3)
         h, w, c = img.shape
@@ -166,6 +192,18 @@ class TestGeometric:
                     assert flipped_img[i, j, k] == img[h - 1 - i, j, k]
                     assert flipped_img[i, j, k] == img_for_flip[i, j, k]
 
+        # test diagonal flip (color image)
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip, direction='diagonal')
+        assert flipped_img.shape == img.shape
+        assert flipped_img.shape == img_for_flip.shape
+        assert id(flipped_img) == id(img_for_flip)
+        for i in range(h):
+            for j in range(w):
+                for k in range(c):
+                    assert flipped_img[i, j, k] == img[h - 1 - i, w - 1 - j, k]
+                    assert flipped_img[i, j, k] == img_for_flip[i, j, k]
+
         # test horizontal flip (grayscale image)
         img = np.random.rand(80, 60)
         h, w = img.shape
@@ -190,6 +228,17 @@ class TestGeometric:
                 assert flipped_img[i, j] == img[h - 1 - i, j]
                 assert flipped_img[i, j] == img_for_flip[i, j]
 
+        # test diagonal flip (grayscale image)
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip, direction='diagonal')
+        assert flipped_img.shape == img.shape
+        assert flipped_img.shape == img_for_flip.shape
+        assert id(flipped_img) == id(img_for_flip)
+        for i in range(h):
+            for j in range(w):
+                assert flipped_img[i, j] == img[h - 1 - i, w - 1 - j]
+                assert flipped_img[i, j] == img_for_flip[i, j]
+
     def test_imcrop(self):
         # yapf: disable
         bboxes = np.array([[100, 100, 199, 199],  # center