[Fix] Set random seed for generating palette if not given. (open-mmlab#1152)

* Fix colors

* fix comments

* Add comments

* Add comments. Add random seed in datasets

Author: jbwang1997

mmseg/datasets/custom.py

@@ -349,7 +349,16 @@ def get_palette_for_custom_classes(self, class_names, palette=None):
 
         elif palette is None:
             if self.PALETTE is None:
+                # Get random state before set seed, and restore
+                # random state later.
+                # It will prevent loss of randomness, as the palette
+                # may be different in each iteration if not specified.
+                # See: https://github.com/open-mmlab/mmdetection/issues/5844
+                state = np.random.get_state()
+                np.random.seed(42)
+                # random palette
                 palette = np.random.randint(0, 255, size=(len(class_names), 3))
+                np.random.set_state(state)
             else:
                 palette = self.PALETTE
 

mmseg/models/segmentors/base.py

@@ -245,8 +245,17 @@ def show_result(self,
         seg = result[0]
         if palette is None:
             if self.PALETTE is None:
+                # Get random state before set seed,
+                # and restore random state later.
+                # It will prevent loss of randomness, as the palette
+                # may be different in each iteration if not specified.
+                # See: https://github.com/open-mmlab/mmdetection/issues/5844
+                state = np.random.get_state()
+                np.random.seed(42)
+                # random palette
                 palette = np.random.randint(
                     0, 255, size=(len(self.CLASSES), 3))
+                np.random.set_state(state)
             else:
                 palette = self.PALETTE
         palette = np.array(palette)