Efficient channel swapping

Author: MatthijsBurgh

mmcv/image/io.py

@@ -284,7 +284,7 @@ def imfrombytes(content: bytes,
         flag = imread_flags[flag] if is_str(flag) else flag
         img = cv2.imdecode(img_np, flag)
         if flag == IMREAD_COLOR and channel_order == 'rgb':
-            cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)
+            img = img[..., ::-1]  # Faster than cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)
         return img
 
 

mmcv/image/photometric.py

@@ -44,7 +44,7 @@ def imnormalize_(img, mean, std, to_rgb=True):
     mean = np.float64(mean.reshape(1, -1))
     stdinv = 1 / np.float64(std.reshape(1, -1))
     if to_rgb:
-        cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)  # inplace
+        img = img[..., ::-1]  # Faster than cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)  # inplace
     cv2.subtract(img, mean, img)  # inplace
     cv2.multiply(img, stdinv, img)  # inplace
     return img
@@ -57,7 +57,7 @@ def imdenormalize(img, mean, std, to_bgr=True):
     img = cv2.multiply(img, std)  # make a copy
     cv2.add(img, mean, img)  # inplace
     if to_bgr:
-        cv2.cvtColor(img, cv2.COLOR_RGB2BGR, img)  # inplace
+        img = img[..., ::-1]  # Faster than cv2.cvtColor(img, cv2.COLOR_RGB2BGR, img)  # inplace
     return img
 
 
@@ -427,7 +427,7 @@ def adjust_lighting(img, eigval, eigvec, alphastd=0.1, to_rgb=True):
 
     img = img.copy().astype(np.float32)
     if to_rgb:
-        cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)  # inplace
+        img = img[..., ::-1]  # Faster than cv2.cvtColor(img, cv2.COLOR_BGR2RGB, img)  # inplace
 
     alpha = np.random.normal(0, alphastd, n_eigval)
     alter = eigvec \