can pass list of integer to set different duration for each frame when saving GIF

PIL/GifImagePlugin.py

@@ -352,10 +352,21 @@ def _save(im, fp, filename, save_all=False):
 
         first_frame = None
         append_images = im.encoderinfo.get("append_images", [])
+        if "duration" in im.encoderinfo:
+            duration = im.encoderinfo["duration"]
+        else:
+            duration = None
+        frame_count = 0
         for imSequence in [im]+append_images:
             for im_frame in ImageSequence.Iterator(imSequence):
                 encoderinfo = im.encoderinfo.copy()
                 im_frame = _convert_mode(im_frame)
+                if duration is not None:
+                    if not isinstance(duration, list):
+                        encoderinfo["duration"] = duration
+                    else:
+                        encoderinfo["duration"] = duration[frame_count]
+                frame_count += 1
 
                 # To specify duration, add the time in milliseconds to getdata(),
                 # e.g. getdata(im_frame, duration=1000)

Tests/test_file_gif.py

@@ -281,6 +281,25 @@ class TestFileGif(PillowTestCase):
 
         self.assertEqual(reread.info['duration'], duration)
 
+    def test_multiple_duration(self):
+        duration_list = [1000, 2000, 3000]
+
+        out = self.tempfile('temp.gif')
+        im_list = [
+            Image.new('L', (100, 100), '#000'),
+            Image.new('L', (100, 100), '#111'),
+            Image.new('L', (100, 100), '#222'),
+        ]
+        im_list[0].save(out, save_all=True, append_images=im_list[1:], duration=duration_list)
+        reread = Image.open(out)
+
+        for duration in duration_list:
+            self.assertEqual(reread.info['duration'], duration)
+            try:
+                reread.seek(reread.tell() + 1)
+            except EOFError:
+                pass
+
     def test_number_of_loops(self):
         number_of_loops = 2
 

docs/handbook/image-file-formats.rst

@@ -111,7 +111,9 @@ additional frames when saving, the ``append_images`` parameter works with
 
 If present, the ``loop`` parameter can be used to set the number of times
 the GIF should loop, and the ``duration`` parameter can set the number of
-milliseconds between each frame.
+milliseconds between each frame. The ``duration`` parameter can be either
+an integer or a list of integer. Passing a list to ``duration`` parameter
+will set the ``duration`` of each frame respectively.
 
 Reading local images
 ~~~~~~~~~~~~~~~~~~~~