diff --git a/pngwutil.c b/pngwutil.c
index 81acc2b..bbd3881 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -1,9 +1,9 @@
 
 /* pngwutil.c - utilities to write a PNG file
  *
- * libpng 1.2.6beta2 - November 1, 2002
+ * libpng version 1.2.6beta3 - July 18, 2004
  * For conditions of distribution and use, see copyright notice in png.h
- * Copyright (c) 1998-2002 Glenn Randers-Pehrson
+ * Copyright (c) 1998-2004 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
  */
@@ -464,6 +464,7 @@
 #if defined(PNG_MNG_FEATURES_SUPPORTED)
    png_ptr->filter_type = (png_byte)filter_type;
 #endif
+   png_ptr->compression_type = (png_byte)compression_type;
    png_ptr->width = width;
    png_ptr->height = height;
 
@@ -596,6 +597,46 @@
    PNG_IDAT;
 #endif
    png_debug(1, "in png_write_IDAT\n");
+
+   /* Optimize the CMF field in the zlib stream. */
+   /* This hack of the zlib stream is compliant to the stream specification. */
+   if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
+       png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
+   {
+      unsigned int z_cmf = data[0];  /* zlib compression method and flags */
+      if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
+      {
+         /* Avoid memory underflows and multiplication overflows. */
+         /* The conditions below are practically always satisfied;
+            however, they still must be checked. */
+         if (length >= 2 &&
+             png_ptr->height < 16384 && png_ptr->width < 16384)
+         {
+            png_uint_32 uncompressed_idat_size = png_ptr->height *
+               ((png_ptr->width *
+                  png_ptr->channels * png_ptr->bit_depth + 15) >> 3);
+            unsigned int z_cinfo = z_cmf >> 4;
+            unsigned int half_z_window_size = 1 << (z_cinfo + 7);
+            while (uncompressed_idat_size <= half_z_window_size &&
+                   half_z_window_size >= 256)
+            {
+               z_cinfo--;
+               half_z_window_size >>= 1;
+            }
+            z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
+            if (data[0] != (png_byte)z_cmf)
+            {
+               data[0] = (png_byte)z_cmf;
+               data[1] &= 0xe0;
+               data[1] += (png_byte)(0x1f - ((z_cmf << 8) + data[1]) % 0x1f);
+            }
+         }
+      }
+      else
+         png_error(png_ptr,
+            "Invalid zlib compression method or flags in IDAT");
+   }
+
    png_write_chunk(png_ptr, (png_bytep)png_IDAT, data, length);
    png_ptr->mode |= PNG_HAVE_IDAT;
 }
@@ -1353,7 +1394,7 @@
    {
       png_warning(png_ptr, "Empty language field in iTXt chunk");
       new_lang = NULL;
-      lang_len = 0;      
+      lang_len = 0;
    }
 
    if (lang_key == NULL)
@@ -2165,7 +2206,7 @@
 
          sum += (v < 128) ? v : 256 - v;
       }
-      for (lp = row_buf + 1; i < row_info->rowbytes;
+      for (lp = row_buf + 1; i < row_bytes;
          i++, rp++, lp++, dp++)
       {
          v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);