From f848993c89753304911830cd14d553db59cf4eac Mon Sep 17 00:00:00 2001
From: David Schmidt <david.schmiddi.86@gmail.com>
Date: Tue, 25 Feb 2014 09:50:42 +0100
Subject: [PATCH 1/3] fixes #528

Accept 0 as transparency value.
---
 PIL/PngImagePlugin.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/PIL/PngImagePlugin.py b/PIL/PngImagePlugin.py
index a6038d9f2..18abf27d3 100644
--- a/PIL/PngImagePlugin.py
+++ b/PIL/PngImagePlugin.py
@@ -561,7 +561,7 @@ def _save(im, fp, filename, chunk=putchunk, check=0):
 
     transparency = im.encoderinfo.get('transparency',im.info.get('transparency', None))
     
-    if transparency:
+    if transparency or transparency == 0:
         if im.mode == "P":
             # limit to actual palette size
             alpha_bytes = 2**bits

From 0d453d9805f203989ac58815fc88358dadb16a8a Mon Sep 17 00:00:00 2001
From: wiredfool <eric-github@soroos.net>
Date: Fri, 28 Feb 2014 16:29:34 -0800
Subject: [PATCH 2/3] Added test for Palette transparency=0

---
 Tests/test_file_png.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/Tests/test_file_png.py b/Tests/test_file_png.py
index e8d2a1208..c17829194 100644
--- a/Tests/test_file_png.py
+++ b/Tests/test_file_png.py
@@ -251,6 +251,20 @@ def test_trns_rgb():
     im = roundtrip(im, transparency=(0, 1, 2))
     assert_equal(im.info["transparency"], (0, 1, 2))
 
+def test_trns_p():
+    # Check writing a transparency of 0, issue #528
+    im = lena('P')
+    im.info['transparency']=0
+    
+    f = tempfile("temp.png")
+    im.save(f)
+
+    im2 = Image.open(f)
+    assert_true('transparency' in im2.info)
+
+    assert_image_equal(im2.convert('RGBA'), im.convert('RGBA'))
+        
+    
 def test_save_icc_profile_none():
     # check saving files with an ICC profile set to None (omit profile)
     in_file = "Tests/images/icc_profile_none.png"

From 7baaf296d27b0a380357efdbbd3789c6e89b37e2 Mon Sep 17 00:00:00 2001
From: wiredfool <eric-github@soroos.net>
Date: Fri, 28 Feb 2014 16:32:55 -0800
Subject: [PATCH 3/3] Updated changes

---
 CHANGES.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/CHANGES.rst b/CHANGES.rst
index 8c28bc415..abdf73b33 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -4,6 +4,9 @@ Changelog (Pillow)
 2.4.0 (unreleased)
 ------------------
 
+- Fixed saving mode P image as a PNG with transparency = palette color 0
+  [d-schmidt]
+
 - Improve heuristic used when saving progressive and optimized JPEGs with high quality values
   [e98cuenc]