Merge pull request #7593 from florath/ImageStat_getextrema_opt

 Optimize ImageStat.Stat._getextrema function

src/PIL/ImageStat.py

@@ -51,13 +51,16 @@ def _getextrema(self):
         """Get min/max values for each band in the image"""
 
         def minmax(histogram):
-            n = 255
-            x = 0
+            res_min, res_max = 255, 0
             for i in range(256):
                 if histogram[i]:
-                    n = min(n, i)
-                    x = max(x, i)
-            return n, x  # returns (255, 0) if there's no data in the histogram
+                    res_min = i
+                    break
+            for i in range(255, -1, -1):
+                if histogram[i]:
+                    res_max = i
+                    break
+            return res_min, res_max
 
         return [minmax(self.h[i:]) for i in range(0, len(self.h), 256)]