[BC-breaking] ColorJitter gets its random params by calling get_params() (pytorch#3001)

* ColorJitter gets its random params by calling get_params().

* Update arguments.

* Styles.

* Add description for Nones.

* Chainging Nones to optional.

Author: datumbox

torchvision/transforms/transforms.py

@@ -1051,38 +1051,35 @@ def _check_input(self, value, name, center=1, bound=(0, float('inf')), clip_firs
         return value
 
     @staticmethod
-    @torch.jit.unused
-    def get_params(brightness, contrast, saturation, hue):
-        """Get a randomized transform to be applied on image.
+    def get_params(brightness: Optional[List[float]],
+                   contrast: Optional[List[float]],
+                   saturation: Optional[List[float]],
+                   hue: Optional[List[float]]
+                   ) -> Tuple[Tensor, Optional[float], Optional[float], Optional[float], Optional[float]]:
+        """Get the parameters for the randomized transform to be applied on image.
 
-        Arguments are same as that of __init__.
+        Args:
+            brightness (tuple of float (min, max), optional): The range from which the brightness_factor is chosen
+                uniformly. Pass None to turn off the transformation.
+            contrast (tuple of float (min, max), optional): The range from which the contrast_factor is chosen
+                uniformly. Pass None to turn off the transformation.
+            saturation (tuple of float (min, max), optional): The range from which the saturation_factor is chosen
+                uniformly. Pass None to turn off the transformation.
+            hue (tuple of float (min, max), optional): The range from which the hue_factor is chosen uniformly.
+                Pass None to turn off the transformation.
 
         Returns:
-            Transform which randomly adjusts brightness, contrast and
-            saturation in a random order.
+            tuple: The parameters used to apply the randomized transform
+            along with their random order.
         """
-        transforms = []
-
-        if brightness is not None:
-            brightness_factor = random.uniform(brightness[0], brightness[1])
-            transforms.append(Lambda(lambda img: F.adjust_brightness(img, brightness_factor)))
-
-        if contrast is not None:
-            contrast_factor = random.uniform(contrast[0], contrast[1])
-            transforms.append(Lambda(lambda img: F.adjust_contrast(img, contrast_factor)))
-
-        if saturation is not None:
-            saturation_factor = random.uniform(saturation[0], saturation[1])
-            transforms.append(Lambda(lambda img: F.adjust_saturation(img, saturation_factor)))
-
-        if hue is not None:
-            hue_factor = random.uniform(hue[0], hue[1])
-            transforms.append(Lambda(lambda img: F.adjust_hue(img, hue_factor)))
+        fn_idx = torch.randperm(4)
 
-        random.shuffle(transforms)
-        transform = Compose(transforms)
+        b = None if brightness is None else float(torch.empty(1).uniform_(brightness[0], brightness[1]))
+        c = None if contrast is None else float(torch.empty(1).uniform_(contrast[0], contrast[1]))
+        s = None if saturation is None else float(torch.empty(1).uniform_(saturation[0], saturation[1]))
+        h = None if hue is None else float(torch.empty(1).uniform_(hue[0], hue[1]))
 
-        return transform
+        return fn_idx, b, c, s, h
 
     def forward(self, img):
         """
@@ -1092,26 +1089,17 @@ def forward(self, img):
         Returns:
             PIL Image or Tensor: Color jittered image.
         """
-        fn_idx = torch.randperm(4)
+        fn_idx, brightness_factor, contrast_factor, saturation_factor, hue_factor = \
+            self.get_params(self.brightness, self.contrast, self.saturation, self.hue)
+
         for fn_id in fn_idx:
-            if fn_id == 0 and self.brightness is not None:
-                brightness = self.brightness
-                brightness_factor = torch.tensor(1.0).uniform_(brightness[0], brightness[1]).item()
+            if fn_id == 0 and brightness_factor is not None:
                 img = F.adjust_brightness(img, brightness_factor)
-
-            if fn_id == 1 and self.contrast is not None:
-                contrast = self.contrast
-                contrast_factor = torch.tensor(1.0).uniform_(contrast[0], contrast[1]).item()
+            elif fn_id == 1 and contrast_factor is not None:
                 img = F.adjust_contrast(img, contrast_factor)
-
-            if fn_id == 2 and self.saturation is not None:
-                saturation = self.saturation
-                saturation_factor = torch.tensor(1.0).uniform_(saturation[0], saturation[1]).item()
+            elif fn_id == 2 and saturation_factor is not None:
                 img = F.adjust_saturation(img, saturation_factor)
-
-            if fn_id == 3 and self.hue is not None:
-                hue = self.hue
-                hue_factor = torch.tensor(1.0).uniform_(hue[0], hue[1]).item()
+            elif fn_id == 3 and hue_factor is not None:
                 img = F.adjust_hue(img, hue_factor)
 
         return img