add inplace imflip (#191)

* add implace flip

* add tests
Signed-off-by: lixuanyi <lixuanyi@sensetime.com>

* modify tests
Signed-off-by: lixuanyi <lixuanyi@sensetime.com>

* add inplace tests
Signed-off-by: lixuanyi <lixuanyi@sensetime.com>

* add comments
Signed-off-by: lixuanyi <lixuanyi@sensetime.com>

* fix
Signed-off-by: lixuanyi <lixuanyi@sensetime.com>

mmcv/image/__init__.py

@@ -2,15 +2,15 @@
 from .io import imfrombytes, imread, imwrite, supported_backends, use_backend
 from .transforms import (bgr2gray, bgr2hls, bgr2hsv, bgr2rgb, gray2bgr,
                          gray2rgb, hls2bgr, hsv2bgr, imcrop, imdenormalize,
-                         imflip, iminvert, imnormalize, impad,
+                         imflip, imflip_, iminvert, imnormalize, impad,
                          impad_to_multiple, imrescale, imresize, imresize_like,
                          imrotate, posterize, rgb2bgr, rgb2gray, solarize)
 
 __all__ = [
     'solarize', 'posterize', 'imread', 'imwrite', 'imfrombytes', 'bgr2gray',
     'rgb2gray', 'gray2bgr', 'gray2rgb', 'bgr2rgb', 'rgb2bgr', 'bgr2hsv',
-    'hsv2bgr', 'bgr2hls', 'hls2bgr', 'iminvert', 'imflip', 'imrotate',
-    'imcrop', 'impad', 'impad_to_multiple', 'imnormalize', 'imdenormalize',
-    'imresize', 'imresize_like', 'imrescale', 'use_backend',
+    'hsv2bgr', 'bgr2hls', 'hls2bgr', 'iminvert', 'imflip', 'imflip_',
+    'imrotate', 'imcrop', 'impad', 'impad_to_multiple', 'imnormalize',
+    'imdenormalize', 'imresize', 'imresize_like', 'imrescale', 'use_backend',
     'supported_backends'
 ]

mmcv/image/transforms/__init__.py

@@ -2,13 +2,15 @@
 from .colorspace import (bgr2gray, bgr2hls, bgr2hsv, bgr2rgb, gray2bgr,
                          gray2rgb, hls2bgr, hsv2bgr, iminvert, posterize,
                          rgb2bgr, rgb2gray, solarize)
-from .geometry import imcrop, imflip, impad, impad_to_multiple, imrotate
+from .geometry import (imcrop, imflip, imflip_, impad, impad_to_multiple,
+                       imrotate)
 from .normalize import imdenormalize, imnormalize
 from .resize import imrescale, imresize, imresize_like
 
 __all__ = [
     'solarize', 'posterize', 'bgr2gray', 'rgb2gray', 'gray2bgr', 'gray2rgb',
     'bgr2rgb', 'rgb2bgr', 'bgr2hsv', 'hsv2bgr', 'bgr2hls', 'hls2bgr',
-    'iminvert', 'imflip', 'imrotate', 'imcrop', 'impad', 'impad_to_multiple',
-    'imnormalize', 'imdenormalize', 'imresize', 'imresize_like', 'imrescale'
+    'iminvert', 'imflip', 'imflip_', 'imrotate', 'imcrop', 'impad',
+    'impad_to_multiple', 'imnormalize', 'imdenormalize', 'imresize',
+    'imresize_like', 'imrescale'
 ]

mmcv/image/transforms/geometry.py

@@ -22,6 +22,22 @@ def imflip(img, direction='horizontal'):
         return np.flip(img, axis=0)
 
 
+def imflip_(img, direction='horizontal'):
+    """Inplace flip an image horizontally or vertically.
+    Args:
+        img (ndarray): Image to be flipped.
+        direction (str): The flip direction, either "horizontal" or "vertical".
+
+    Returns:
+        ndarray: The flipped image(inplace).
+    """
+    assert direction in ['horizontal', 'vertical']
+    if direction == 'horizontal':
+        return cv2.flip(img, 1, img)
+    else:
+        return cv2.flip(img, 0, img)
+
+
 def imrotate(img,
              angle,
              center=None,

tests/test_image.py

@@ -313,6 +313,57 @@ class TestImage(object):
             for j in range(w):
                 assert flipped_img[i, j] == img[h - 1 - i, j]
 
+    def test_imflip_(self):
+        # test horizontal flip (color image)
+        img = np.random.rand(80, 60, 3)
+        h, w, c = img.shape
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip)
+        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[i, w - 1 - j, k]
+                    assert flipped_img[i, j, k] == img_for_flip[i, j, k]
+
+        # test vertical flip (color image)
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip, direction='vertical')
+        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, 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
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip)
+        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[i, w - 1 - j]
+                assert flipped_img[i, j] == img_for_flip[i, j]
+
+        # test vertical flip (grayscale image)
+        img_for_flip = img.copy()
+        flipped_img = mmcv.imflip_(img_for_flip, direction='vertical')
+        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, 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