Merge pull request #2313 from wiredfool/pr_2196

Unified different GIF optimize conditions #2196, Test for #2196

PIL/GifImagePlugin.py

@@ -434,13 +434,11 @@ def _get_local_header(fp, im, offset, flags):
         # optimize the block away if transparent color is not used
         transparent_color_exists = True
 
-        if _get_optimize(im, im.encoderinfo):
+        used_palette_colors = _get_optimize(im, im.encoderinfo)
-            used_palette_colors = _get_used_palette_colors(im)
+        if used_palette_colors is not None:
-
             # adjust the transparency index after optimize
-            if len(used_palette_colors) < 256:
+            for i, palette_color in enumerate(used_palette_colors):
-                for i in range(len(used_palette_colors)):
+                if palette_color == transparency:
-                    if used_palette_colors[i] == transparency:
                     transparency = i
                     transparent_color_exists = True
                     break
@@ -552,9 +550,28 @@ def _save_netpbm(im, fp, filename):
 # --------------------------------------------------------------------
 # GIF utilities
 
-def _get_optimize(im, info):
+# Force optimization so that we can test performance against
-    return im.mode in ("P", "L") and info and info.get("optimize", 0)
+# cases where it took lots of memory and time previously.
+_FORCE_OPTIMIZE = False
 
+def _get_optimize(im, info):
+    if im.mode in ("P", "L") and info and info.get("optimize", 0):
+        # Potentially expensive operation.
+
+        # The palette saves 3 bytes per color not used, but palette
+        # lengths are restricted to 3*(2**N) bytes. Max saving would
+        # be 768 -> 6 bytes if we went all the way down to 2 colors.
+        # * If we're over 128 colors, we can't save any space.
+        # * If there aren't any holes, it's not worth collapsing.
+        # * If we have a 'large' image, the palette is in the noise.
+
+        # create the new palette if not every color is used
+        used_palette_colors = _get_used_palette_colors(im)
+        if _FORCE_OPTIMIZE or im.mode == 'L' or \
+           (len(used_palette_colors) <= 128 and
+            max(used_palette_colors) > len(used_palette_colors) and
+            im.width * im.height < 512 * 512):
+            return used_palette_colors
 
 def _get_used_palette_colors(im):
     used_palette_colors = []
@@ -586,10 +603,6 @@ def _get_header_palette(palette_bytes):
         palette_bytes += o8(0) * 3 * actual_target_size_diff
     return palette_bytes
 
-# Force optimization so that we can test performance against
-# cases where it took lots of memory and time previously. 
-_FORCE_OPTIMIZE = False
-
 def _get_palette_bytes(im, palette, info):
     if im.mode == "P":
         if palette and isinstance(palette, bytes):
@@ -602,25 +615,10 @@ def _get_palette_bytes(im, palette, info):
         else:
             source_palette = bytearray(i//3 for i in range(768))
 
-    used_palette_colors = palette_bytes = None
+    palette_bytes = None
 
-    if _get_optimize(im, info):
+    used_palette_colors = _get_optimize(im, info)
-        used_palette_colors = _get_used_palette_colors(im)
+    if used_palette_colors is not None:
-
-        # Potentially expensive operation.
-
-        # The palette saves 3 bytes per color not used, but palette
-        # lengths are restricted to 3*(2**N) bytes. Max saving would
-        # be 768 -> 6 bytes if we went all the way down to 2 colors.
-        # * If we're over 128 colors, we can't save any space.
-        # * If there aren't any holes, it's not worth collapsing. 
-        # * If we have a 'large' image, the palette is in the noise.
-
-        # create the new palette if not every color is used
-        if _FORCE_OPTIMIZE or im.mode == 'L' or \
-               (len(used_palette_colors) <= 128 and  
-                max(used_palette_colors) > len(used_palette_colors) and
-                im.width * im.height < 512 * 512):
         palette_bytes = b""
         new_positions = [0]*256
 

Tests/test_file_gif.py

@@ -362,5 +362,28 @@ class TestFileGif(PillowTestCase):
         reread = Image.open(out)
         self.assertEqual(reread.n_frames, 10)
 
+    def test_transparent_optimize(self):
+        # from issue #2195, if the transparent color is incorrectly
+        # optimized out, gif loses transparency Need a palette that
+        # isn't using the 0 color, and one that's > 128 items where
+        # the transparent color is actually the top palette entry to
+        # trigger the bug.
+
+        from PIL import ImagePalette
+
+        data = bytes(bytearray(range(1,254)))
+        palette = ImagePalette.ImagePalette("RGB", list(range(256))*3)
+
+        im = Image.new('L', (253,1))
+        im.frombytes(data)
+        im.putpalette(palette)
+
+        out = self.tempfile('temp.gif')
+        im.save(out, transparency=253)
+        reloaded = Image.open(out)
+
+        self.assertEqual(reloaded.info['transparency'], 253)
+        
+
 if __name__ == '__main__':
     unittest.main()