normalise updates (#699)

* normalise

* some changes

* Update functional.py

* Update functional.py

* code changes

torchvision/transforms/functional.py

@@ -181,11 +181,11 @@ def to_pil_image(pic, mode=None):
     return Image.fromarray(npimg, mode=mode)
 
 
-def normalize(tensor, mean, std):
+def normalize(tensor, mean, std, inplace=False):
     """Normalize a tensor image with mean and standard deviation.
 
     .. note::
-        This transform acts in-place, i.e., it mutates the input tensor.
+        This transform acts out of place by default, i.e., it does not mutates the input tensor.
 
     See :class:`~torchvision.transforms.Normalize` for more details.
 
@@ -200,9 +200,12 @@ def normalize(tensor, mean, std):
     if not _is_tensor_image(tensor):
         raise TypeError('tensor is not a torch image.')
 
-    # This is faster than using broadcasting, don't change without benchmarking
-    for t, m, s in zip(tensor, mean, std):
-        t.sub_(m).div_(s)
+    if not inplace:
+        tensor = tensor.clone()
+
+    mean = torch.tensor(mean, dtype=torch.float32)
+    std = torch.tensor(std, dtype=torch.float32)
+    tensor.sub_(mean[:, None, None]).div_(std[:, None, None])
     return tensor
 
 

torchvision/transforms/transforms.py

@@ -136,16 +136,17 @@ class Normalize(object):
     ``input[channel] = (input[channel] - mean[channel]) / std[channel]``
 
     .. note::
-        This transform acts in-place, i.e., it mutates the input tensor.
+        This transform acts out of place, i.e., it does not mutates the input tensor.
 
     Args:
         mean (sequence): Sequence of means for each channel.
         std (sequence): Sequence of standard deviations for each channel.
     """
 
-    def __init__(self, mean, std):
+    def __init__(self, mean, std, inplace=False):
         self.mean = mean
         self.std = std
+        self.inplace = inplace
 
     def __call__(self, tensor):
         """
@@ -155,7 +156,7 @@ class Normalize(object):
         Returns:
             Tensor: Normalized Tensor image.
         """
-        return F.normalize(tensor, self.mean, self.std)
+        return F.normalize(tensor, self.mean, self.std, self.inplace)
 
     def __repr__(self):
         return self.__class__.__name__ + '(mean={0}, std={1})'.format(self.mean, self.std)