From 636d4caeb3bc8d41a944b326649f5bd769be5298 Mon Sep 17 00:00:00 2001
From: Yusuke Shinyama <yusuke@shinyama.jp>
Date: Mon, 24 Mar 2014 19:57:05 +0900
Subject: [PATCH] Fixed the PNG predictor bug. Thanks to Gabor Molnar.

---
 pdfminer/utils.py | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/pdfminer/utils.py b/pdfminer/utils.py
index 5329640..ca1b30f 100644
--- a/pdfminer/utils.py
+++ b/pdfminer/utils.py
@@ -16,35 +16,36 @@ def apply_png_predictor(pred, colors, columns, bitspercomponent, data):
     i = 0
     buf = ''
     line0 = '\x00' * columns
-    while i < len(data):
-        pred = data[i]
+    for i in xrange(0, len(data), nbytes+1):
+        ft = data[i]
         i += 1
         line1 = data[i:i+nbytes]
-        i += nbytes
-        if pred == '\x00':
+        line2 = ''
+        if ft == '\x00':
             # PNG none
-            buf += line1
-        elif pred == '\x01':
+            line2 += line1
+        elif ft == '\x01':
             # PNG sub (UNTESTED)
             c = 0
             for b in line1:
                 c = (c+ord(b)) & 255
-                buf += chr(c)
-        elif pred == '\x02':
+                line2 += chr(c)
+        elif ft == '\x02':
             # PNG up
             for (a, b) in zip(line0, line1):
                 c = (ord(a)+ord(b)) & 255
-                buf += chr(c)
-        elif pred == '\x03':
+                line2 += chr(c)
+        elif ft == '\x03':
             # PNG average (UNTESTED)
             c = 0
             for (a, b) in zip(line0, line1):
                 c = ((c+ord(a)+ord(b))//2) & 255
-                buf += chr(c)
+                line2 += chr(c)
         else:
             # unsupported
-            raise ValueError(pred)
-        line0 = line1
+            raise ValueError(ft)
+        buf += line2
+        line0 = line2
     return buf