generalization of Expand transfrom probability (#1633)

Allows to use not only 0.5 probability.

mmdet/datasets/pipelines/transforms.py

@@ -509,13 +509,15 @@ class Expand(object):
         mean (tuple): mean value of dataset.
         to_rgb (bool): if need to convert the order of mean to align with RGB.
         ratio_range (tuple): range of expand ratio.
+        prob (float): probability of applying this transformation
     """
 
     def __init__(self,
                  mean=(0, 0, 0),
                  to_rgb=True,
                  ratio_range=(1, 4),
-                 seg_ignore_label=None):
+                 seg_ignore_label=None,
+                 prob=0.5):
         self.to_rgb = to_rgb
         self.ratio_range = ratio_range
         if to_rgb:
@@ -524,9 +526,10 @@ class Expand(object):
             self.mean = mean
         self.min_ratio, self.max_ratio = ratio_range
         self.seg_ignore_label = seg_ignore_label
+        self.prob = prob
 
     def __call__(self, results):
-        if random.randint(2):
+        if random.uniform(0, 1) > self.prob:
             return results
 
         img, boxes = [results[k] for k in ('img', 'gt_bboxes')]