Add rgb2gray and gray2rgb (#139)

* add rgb2gray and gray2rgb

* update version

* minor fix for the docstring

mmcv/image/__init__.py

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

mmcv/image/transforms/__init__.py

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

mmcv/image/transforms/colorspace.py

@@ -59,11 +59,28 @@ def bgr2gray(img, keepdim=False):
     return out_img
 
 
+def rgb2gray(img, keepdim=False):
+    """Convert a RGB image to grayscale image.
+
+    Args:
+        img (ndarray): The input image.
+        keepdim (bool): If False (by default), then return the grayscale image
+            with 2 dims, otherwise 3 dims.
+
+    Returns:
+        ndarray: The converted grayscale image.
+    """
+    out_img = cv2.cvtColor(img, cv2.COLOR_RGB2GRAY)
+    if keepdim:
+        out_img = out_img[..., None]
+    return out_img
+
+
 def gray2bgr(img):
     """Convert a grayscale image to BGR image.
 
     Args:
-        img (ndarray or str): The input image.
+        img (ndarray): The input image.
 
     Returns:
         ndarray: The converted BGR image.
@@ -73,6 +90,20 @@ def gray2bgr(img):
     return out_img
 
 
+def gray2rgb(img):
+    """Convert a grayscale image to RGB image.
+
+    Args:
+        img (ndarray): The input image.
+
+    Returns:
+        ndarray: The converted BGR image.
+    """
+    img = img[..., None] if img.ndim == 2 else img
+    out_img = cv2.cvtColor(img, cv2.COLOR_GRAY2RGB)
+    return out_img
+
+
 def convert_color_factory(src, dst):
 
     code = getattr(cv2, 'COLOR_{}2{}'.format(src.upper(), dst.upper()))

mmcv/version.py

-__version__ = '0.2.13'
+__version__ = '0.2.14'

tests/test_image.py

@@ -66,6 +66,17 @@ class TestImage(object):
         assert out_img_3d.shape == (10, 10, 1)
         assert_array_almost_equal(out_img_3d[..., 0], out_img, decimal=4)
 
+    def test_rgb2gray(self):
+        in_img = np.random.rand(10, 10, 3).astype(np.float32)
+        out_img = mmcv.rgb2gray(in_img)
+        computed_gray = (
+            in_img[:, :, 0] * 0.299 + in_img[:, :, 1] * 0.587 +
+            in_img[:, :, 2] * 0.114)
+        assert_array_almost_equal(out_img, computed_gray, decimal=4)
+        out_img_3d = mmcv.rgb2gray(in_img, True)
+        assert out_img_3d.shape == (10, 10, 1)
+        assert_array_almost_equal(out_img_3d[..., 0], out_img, decimal=4)
+
     def test_gray2bgr(self):
         in_img = np.random.rand(10, 10).astype(np.float32)
         out_img = mmcv.gray2bgr(in_img)
@@ -73,6 +84,13 @@ class TestImage(object):
         for i in range(3):
             assert_array_almost_equal(out_img[..., i], in_img, decimal=4)
 
+    def test_gray2rgb(self):
+        in_img = np.random.rand(10, 10).astype(np.float32)
+        out_img = mmcv.gray2rgb(in_img)
+        assert out_img.shape == (10, 10, 3)
+        for i in range(3):
+            assert_array_almost_equal(out_img[..., i], in_img, decimal=4)
+
     def test_bgr2rgb(self):
         in_img = np.random.rand(10, 10, 3).astype(np.float32)
         out_img = mmcv.bgr2rgb(in_img)