From 8c60753db6b44fe99de849a4893955e92d97c340 Mon Sep 17 00:00:00 2001
From: Jon Burgess <jburgess777@gmail.com>
Date: Sat, 13 Jun 2009 18:27:44 +0000
Subject: [PATCH] Fix reduce_4() to make it consistent with reduce_8(). This
 was breaking tiles which were compressing down to a 16 entry colormap. All
 the pixels were being set to the alpha index.

---
 include/mapnik/png_io.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/mapnik/png_io.hpp b/include/mapnik/png_io.hpp
index 6701fd28c..16bf69049 100644
--- a/include/mapnik/png_io.hpp
+++ b/include/mapnik/png_io.hpp
@@ -126,7 +126,7 @@ namespace mapnik {
             mapnik::rgb c((val)&0xff, (val>>8)&0xff, (val>>16) & 0xff);
             byte index = tree.quantize(c);
             if (x%2 >  0) index = index<<4;
-            if ((val>>24)^0x80) index = 0;//alfa
+            if (!((val>>24)&0x80)) index = 0;//alfa
             row_out[x>>1] |= index;
          }
       }