Merge a190d64165 into 86ab020736

CHANGES.rst

@@ -4,6 +4,9 @@ Changelog (Pillow)
 2.4.0 (unreleased)
 ------------------
 
+- Conversions enabled from RGBA->P, Fixes #544
+  [wiredfool]
+
 - Add more detailed error messages to Image.py 
   [larsmans]
 

PIL/Image.py

@@ -735,6 +735,9 @@ class Image:
             im = self.im.convert_matrix(mode, matrix)
             return self._new(im)
 
+        if mode == "P" and self.mode == "RGBA":
+            return self.quantize(colors)
+
         if mode == "P" and palette == ADAPTIVE:
             im = self.im.quantize(colors)
             new = self._new(im)
@@ -762,7 +765,7 @@ class Image:
 
         return self._new(im)
 
-    def quantize(self, colors=256, method=0, kmeans=0, palette=None):
+    def quantize(self, colors=256, method=None, kmeans=0, palette=None):
 
         # methods:
         #    0 = median cut
@@ -774,6 +777,17 @@ class Image:
 
         self.load()
         
+        if method is None:
+            # defaults:
+            method = 0
+            if self.mode == 'RGBA':
+                method = 2
+
+        if self.mode == 'RGBA' and method != 2:
+            # Caller specified an invalid mode. 
+            raise ValueError('Fast Octree (method == 2) is the ' +
+                             ' only valid method for quantizing RGBA images')
+        
         if palette:
             # use palette from reference image
             palette.load()

Tests/test_image_convert.py

@@ -46,5 +46,13 @@ def test_16bit_workaround():
     im = Image.open('Tests/images/16bit.cropped.tif')
     _test_float_conversion(im.convert('I'))
     
+def test_rgba_p():
+    im = lena('RGBA')
+    im.putalpha(lena('L'))
+
+    converted = im.convert('P')
+    comparable = converted.convert('RGBA')
+
+    assert_image_similar(im, comparable, 20)
                
     

Tests/test_image_quantize.py

@@ -20,3 +20,8 @@ def test_octree_quantize():
     assert_image(im, "P", im.size)
 
     assert len(im.getcolors()) == 100
+
+def test_rgba_quantize():
+    im = lena('RGBA')
+    assert_no_exception(lambda: im.quantize())
+    assert_exception(Exception, lambda: im.quantize(method=0))