diff --git a/picksmaller b/picksmaller
new file mode 100755
index 000000000..3c73a446b
--- /dev/null
+++ b/picksmaller
@@ -0,0 +1,27 @@
+#!/bin/sh
+
+# For use in the pngzop project
+# Copyright 2013 by Glenn Randers-Pehrson
+# Released under the pngcrush license (equivalent to the libpng license)
+
+# Selects the smaller of file.zdat (extracted from a PNG) or
+# file.idat.zlib (same but recompressed with zopfli)
+
+# picksmall file1 file2
+
+for file in $*
+do
+file1=$1
+file2=`echo $file1 | sed -e "s/zdat/idat.zlib/"`
+shift
+
+size1=`ls -l $file1 | sed -e "s/[^ ]* [^ ]* [^ ]* [^ ]* //" -e "s/ .*//"`
+size2=`ls -l $file2 | sed -e "s/[^ ]* [^ ]* [^ ]* [^ ]* //" -e "s/ .*//"`
+
+if [ $size1 -le $size2 ] ; then
+echo $file1
+else
+echo $file2
+fi
+
+done
diff --git a/pngidat b/pngidat
index 327acd26b..a2b1f49de 100644
--- a/pngidat
+++ b/pngidat
@@ -1,5 +1,12 @@
 #!/bin/sh
 
+# For use in the pngzop project
+# Copyright 2013 by Glenn Randers-Pehrson
+# Released under the pngcrush license (equivalent to the libpng license)
+
+# Extracts and decompresses the data from the IDAT chunks in a set of
+# PNG files.
+
 for x in $*
 do
   root=`echo $1 | sed -e s/.png$//`
diff --git a/pngidat.c b/pngidat.c
index 0ca30ac09..6f4792cb1 100644
--- a/pngidat.c
+++ b/pngidat.c
@@ -1,18 +1,21 @@
 #include <stdio.h>
 
-/* Copyright 2013 Glenn Randers-Pehrson */
+/* Copyright 2013 Glenn Randers-Pehrson
+ * Released under the pngcrush license (equivalent to the libpng license)
+ */
 
 /* Usage:            
- * pngidat.exe < file.png | pigz -d > file.idat
+ * pngidat.exe < file.png > file.zdat
+ *
+ * file.idat is the zlib datastream from the PNG IDAT chunks.
  *
- * file.idat is the image datastream, with the filter bytes.
  */
 
 main()
 {
-   int i;
-   int buf[5];
-   int c;
+   unsigned int i;
+   unsigned int buf[5];
+   unsigned int c;
 
    buf[4]='\0';
 
@@ -23,7 +26,7 @@ main()
 for (;;)
 {
    /* read length */
-   int length;
+   unsigned int length;
    buf[0]=getchar();
    if (buf[0] == EOF)
       break;
@@ -46,7 +49,9 @@ for (;;)
             break;
          putchar(c);
       }
-      /* skip crc byte */
+      if (c == EOF)
+         break;
+      /* skip crc bytes */
       for (i=4; i; i--)
       {
          c=getchar();
@@ -59,7 +64,13 @@ for (;;)
    else
    {
       for (i=length+4; i; i--)
+      {
          c=getchar();
+         if (c == EOF)
+            break;
+      }
+      if (c == EOF)
+         break;
    }
 }
 }
diff --git a/pngzdat b/pngzdat
index 7631d48ab..a51cdba76 100755
--- a/pngzdat
+++ b/pngzdat
@@ -1,5 +1,11 @@
 #!/bin/sh
 
+# For use in the pngzop project
+# Copyright 2013 by Glenn Randers-Pehrson
+# Released under the pngcrush license (equivalent to the libpng license)
+
+# Extracts the data from the IDAT chunks in a set of # PNG files.
+
 for x in $*
 do
   root=`echo $1 | sed -e s/.png$//`