Optimize ImageStat.Stat._getextrema function

The optimzed function improves the performance. The original function always runs through the complete historgram of length 256 even if it is possible to exit the loop early (break). Running some tests I found performance improvements of factor >10 depending on the image. Signed-off-by: Andreas Florath <[email protected]>
python-pillow · Dec 1, 2023 · 1b8f9d3 · 1b8f9d3
1 parent 76446ee
commit 1b8f9d3
Showing 1 changed file with 12 additions and 6 deletions.
diff --git a/src/PIL/ImageStat.py b/src/PIL/ImageStat.py
@@ -53,17 +53,23 @@ 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
+            if res_max >= res_min:
+                return res_min, res_max
+            else:
+                return (255, 0)
 
         v = []
         for i in range(0, len(self.h), 256):
-            v.append(minmax(self.h[i:]))
+            v.append(minmax(self.h[i:i+256]))
         return v
 
     def _getcount(self):