avoid divide by zero

frigate/motion.py

@@ -40,10 +40,12 @@ class MotionDetector:
         # Improve contrast
         minval = np.percentile(resized_frame, 4)
         maxval = np.percentile(resized_frame, 96)
-        resized_frame = np.clip(resized_frame, minval, maxval)
-        resized_frame = (((resized_frame - minval) / (maxval - minval)) * 255).astype(
-            np.uint8
-        )
+        # don't adjust if the image is a single color
+        if minval < maxval:
+            resized_frame = np.clip(resized_frame, minval, maxval)
+            resized_frame = (
+                ((resized_frame - minval) / (maxval - minval)) * 255
+            ).astype(np.uint8)
 
         # mask frame
         resized_frame[self.mask] = [255]