diff --git a/ANNOUNCE b/ANNOUNCE
index 609faf8..bd7367d 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.2.15rc3 - December 25, 2006
+Libpng 1.2.15rc4 - December 27, 2006
 
 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -9,32 +9,32 @@
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   libpng-1.2.15rc3.tar.gz
-   libpng-1.2.15rc3.tar.bz2
+   libpng-1.2.15rc4.tar.gz
+   libpng-1.2.15rc4.tar.bz2
 
 Source files with LF line endings (for Unix/Linux) without the
 "configure" script
 
-   libpng-1.2.15rc3-no-config.tar.gz
-   libpng-1.2.15rc3-no-config.tar.bz2
+   libpng-1.2.15rc4-no-config.tar.gz
+   libpng-1.2.15rc4-no-config.tar.bz2
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lp1215r03.zip
-   lp1215r03.tar.bz2
+   lp1215r04.zip
+   lp1215r04.tar.bz2
 
 Project files
 
-   libpng-1.2.15rc3-project-netware.zip
-   libpng-1.2.15rc3-project-wince.zip
+   libpng-1.2.15rc4-project-netware.zip
+   libpng-1.2.15rc4-project-wince.zip
 
 Other information:
 
-   libpng-1.2.15rc3-README.txt
-   libpng-1.2.15rc3-KNOWNBUGS.txt
-   libpng-1.2.15rc3-LICENSE.txt
-   libpng-1.2.15rc3-Y2K-compliance.txt
+   libpng-1.2.15rc4-README.txt
+   libpng-1.2.15rc4-KNOWNBUGS.txt
+   libpng-1.2.15rc4-LICENSE.txt
+   libpng-1.2.15rc4-Y2K-compliance.txt
 
 Changes since the last public release (1.2.14):
 
@@ -69,7 +69,11 @@
 version 1.2.15rc3 [December 25, 2006]
   Fixed shared library numbering error that was intruduced in 1.2.15beta6.
 
+version 1.2.15rc4 [December 27, 2006]
+  Fixed handling of rgb_to_gray when png_ptr->color.gray isn't set.
+
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
+
 (subscription required; visit 
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 to subscribe) or to glennrp at users.sourceforge.net
diff --git a/CHANGES b/CHANGES
index 329a17a..60522c8 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1671,6 +1671,9 @@
 version 1.2.15rc3 [December 25, 2006]
   Fixed shared library numbering error that was intruduced in 1.2.15beta6.
 
+version 1.2.15rc4 [December 27, 2006]
+  Fixed handling of rgb_to_gray when png_ptr->color.gray isn't set.
+
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
diff --git a/INSTALL b/INSTALL
index 9daca1a..b3a0e3b 100644
--- a/INSTALL
+++ b/INSTALL
@@ -1,5 +1,5 @@
 
-Installing libpng version 1.2.15rc3 - December 25, 2006
+Installing libpng version 1.2.15rc4 - December 27, 2006
 
 On Unix/Linux and similar systems, you can simply type
 
@@ -44,7 +44,7 @@
 correspond to the version of zlib that's installed.
 
 You can rename the directories that you downloaded (they
-might be called "libpng-1.2.15rc3" or "lpng109" and "zlib-1.2.1"
+might be called "libpng-1.2.15rc4" or "lpng109" and "zlib-1.2.1"
 or "zlib121") so that you have directories called "zlib" and "libpng".
 
 Your directory structure should look like this:
@@ -101,14 +101,14 @@
  CMakeLists.txt    =>  "cmake" script
  makefile.std      =>  Generic UNIX makefile (cc, creates static libpng.a)
  makefile.elf      =>  Linux/ELF makefile symbol versioning,
-                       gcc, creates libpng12.so.0.1.2.15rc3)
+                       gcc, creates libpng12.so.0.1.2.15rc4)
  makefile.linux    =>  Linux/ELF makefile
-                       (gcc, creates libpng12.so.0.1.2.15rc3)
+                       (gcc, creates libpng12.so.0.1.2.15rc4)
  makefile.gcmmx    =>  Linux/ELF makefile
-                       (gcc, creates libpng12.so.0.1.2.15rc3,
+                       (gcc, creates libpng12.so.0.1.2.15rc4,
                        uses assembler code tuned for Intel MMX platform)
  makefile.nommx    =>  Linux/ELF makefile
-                       (gcc, creates libpng12.so.0.1.2.15rc3
+                       (gcc, creates libpng12.so.0.1.2.15rc4
                        does not use Intel MMX assembler code)
  makefile.gcc      =>  Generic makefile (gcc, creates static libpng.a)
  makefile.knr      =>  Archaic UNIX Makefile that converts files with
@@ -131,12 +131,12 @@
  makefile.openbsd  =>  OpenBSD makefile
  makefile.sgi      =>  Silicon Graphics IRIX makefile (cc, creates static lib)
  makefile.sggcc    =>  Silicon Graphics (gcc,
-                       creates libpng12.so.0.1.2.15rc3)
+                       creates libpng12.so.0.1.2.15rc4)
  makefile.sunos    =>  Sun makefile
  makefile.solaris  =>  Solaris 2.X makefile (gcc,
-                       creates libpng12.so.0.1.2.15rc3)
+                       creates libpng12.so.0.1.2.15rc4)
  makefile.so9      =>  Solaris 9 makefile (gcc,
-                       creates libpng12.so.0.1.2.15rc3)
+                       creates libpng12.so.0.1.2.15rc4)
  makefile.32sunu   =>  Sun Ultra 32-bit makefile
  makefile.64sunu   =>  Sun Ultra 64-bit makefile
  makefile.sco      =>  For SCO OSr5  ELF and Unixware 7 with Native cc
diff --git a/KNOWNBUG b/KNOWNBUG
index a44dd73..5cbc53b 100644
--- a/KNOWNBUG
+++ b/KNOWNBUG
@@ -1,5 +1,5 @@
 
-Known bugs in libpng version 1.2.15rc3
+Known bugs in libpng version 1.2.15rc4
 
 1. April 22, 2001: pnggccrd.c has been reported to crash on NetBSD when
    reading interlaced PNG files, when assembler code is enabled but running
diff --git a/LICENSE b/LICENSE
index 5df77e8..b38dcec 100644
--- a/LICENSE
+++ b/LICENSE
@@ -8,7 +8,7 @@
 If you modify libpng you may insert additional notices immediately following
 this sentence.
 
-libpng versions 1.2.6, August 15, 2004, through 1.2.15rc3, December 25, 2006, are
+libpng versions 1.2.6, August 15, 2004, through 1.2.15rc4, December 27, 2006, are
 Copyright (c) 2004, 2006 Glenn Randers-Pehrson, and are
 distributed according to the same disclaimer and license as libpng-1.2.5
 with the following individual added to the list of Contributing Authors
@@ -106,4 +106,4 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-December 25, 2006
+December 27, 2006
diff --git a/README b/README
index 4d2e4a5..26a7bc8 100644
--- a/README
+++ b/README
@@ -1,4 +1,4 @@
-README for libpng version 1.2.15rc3 - December 25, 2006 (shared library 12.0)
+README for libpng version 1.2.15rc4 - December 27, 2006 (shared library 12.0)
 See the note about version numbers near the top of png.h
 
 See INSTALL for instructions on how to install libpng.
@@ -190,11 +190,11 @@
        descrip.mms      =>  VMS makefile for MMS or MMK
        makefile.std     =>  Generic UNIX makefile (cc, creates static libpng.a)
        makefile.elf     =>  Linux/ELF makefile symbol versioning,
-                            gcc, creates libpng12.so.0.1.2.15rc3)
+                            gcc, creates libpng12.so.0.1.2.15rc4)
        makefile.linux   =>  Linux/ELF makefile
-                            (gcc, creates libpng12.so.0.1.2.15rc3)
+                            (gcc, creates libpng12.so.0.1.2.15rc4)
        makefile.gcmmx   =>  Linux/ELF makefile
-                            (gcc, creates libpng12.so.0.1.2.15rc3,
+                            (gcc, creates libpng12.so.0.1.2.15rc4,
                             uses assembler code tuned for Intel MMX platform)
        makefile.gcc     =>  Generic makefile (gcc, creates static libpng.a)
        makefile.knr     =>  Archaic UNIX Makefile that converts files with
@@ -216,12 +216,12 @@
        makefile.openbsd =>  OpenBSD makefile
        makefile.sgi     =>  Silicon Graphics IRIX (cc, creates static lib)
        makefile.sggcc   =>  Silicon Graphics
-                            (gcc, creates libpng12.so.0.1.2.15rc3)
+                            (gcc, creates libpng12.so.0.1.2.15rc4)
        makefile.sunos   =>  Sun makefile
        makefile.solaris =>  Solaris 2.X makefile
-                            (gcc, creates libpng12.so.0.1.2.15rc3)
+                            (gcc, creates libpng12.so.0.1.2.15rc4)
        makefile.so9     =>  Solaris 9 makefile
-                            (gcc, creates libpng12.so.0.1.2.15rc3)
+                            (gcc, creates libpng12.so.0.1.2.15rc4)
        makefile.32sunu  =>  Sun Ultra 32-bit makefile
        makefile.64sunu  =>  Sun Ultra 64-bit makefile
        makefile.sco     =>  For SCO OSr5  ELF and Unixware 7 with Native cc
diff --git a/Y2KINFO b/Y2KINFO
index 59bdd19..3d805e9 100644
--- a/Y2KINFO
+++ b/Y2KINFO
@@ -1,13 +1,13 @@
    Y2K compliance in libpng:
    =========================
 
-      December 25, 2006
+      December 27, 2006
 
       Since the PNG Development group is an ad-hoc body, we can't make
       an official declaration.
 
       This is your unofficial assurance that libpng from version 0.71 and
-      upward through 1.2.15rc3 are Y2K compliant.  It is my belief that earlier
+      upward through 1.2.15rc4 are Y2K compliant.  It is my belief that earlier
       versions were also Y2K compliant.
 
       Libpng only has three year fields.  One is a 2-byte unsigned integer
diff --git a/configure b/configure
index 2fa2ecc..01f4057 100755
--- a/configure
+++ b/configure
@@ -1,6 +1,6 @@
 #! /bin/sh
 # Guess values for system-dependent variables and create Makefiles.
-# Generated by GNU Autoconf 2.61 for libpng 1.2.15rc3.
+# Generated by GNU Autoconf 2.61 for libpng 1.2.15rc4.
 #
 # Report bugs to <png-mng-implement@lists.sourceforge.net>.
 #
@@ -728,8 +728,8 @@
 # Identity of this package.
 PACKAGE_NAME='libpng'
 PACKAGE_TARNAME='libpng'
-PACKAGE_VERSION='1.2.15rc3'
-PACKAGE_STRING='libpng 1.2.15rc3'
+PACKAGE_VERSION='1.2.15rc4'
+PACKAGE_STRING='libpng 1.2.15rc4'
 PACKAGE_BUGREPORT='png-mng-implement@lists.sourceforge.net'
 
 ac_unique_file="pngget.c"
@@ -1405,7 +1405,7 @@
   # Omit some internal or obsolete options to make the list less imposing.
   # This message is too long to be a string in the A/UX 3.1 sh.
   cat <<_ACEOF
-\`configure' configures libpng 1.2.15rc3 to adapt to many kinds of systems.
+\`configure' configures libpng 1.2.15rc4 to adapt to many kinds of systems.
 
 Usage: $0 [OPTION]... [VAR=VALUE]...
 
@@ -1475,7 +1475,7 @@
 
 if test -n "$ac_init_help"; then
   case $ac_init_help in
-     short | recursive ) echo "Configuration of libpng 1.2.15rc3:";;
+     short | recursive ) echo "Configuration of libpng 1.2.15rc4:";;
    esac
   cat <<\_ACEOF
 
@@ -1585,7 +1585,7 @@
 test -n "$ac_init_help" && exit $ac_status
 if $ac_init_version; then
   cat <<\_ACEOF
-libpng configure 1.2.15rc3
+libpng configure 1.2.15rc4
 generated by GNU Autoconf 2.61
 
 Copyright (C) 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001,
@@ -1599,7 +1599,7 @@
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
 
-It was created by libpng $as_me 1.2.15rc3, which was
+It was created by libpng $as_me 1.2.15rc4, which was
 generated by GNU Autoconf 2.61.  Invocation command line was
 
   $ $0 $@
@@ -2269,7 +2269,7 @@
 
 # Define the identity of the package.
  PACKAGE='libpng'
- VERSION='1.2.15rc3'
+ VERSION='1.2.15rc4'
 
 
 cat >>confdefs.h <<_ACEOF
@@ -2440,7 +2440,7 @@
 
 
 
-PNGLIB_VERSION=1.2.15rc3
+PNGLIB_VERSION=1.2.15rc4
 PNGLIB_MAJOR=1
 PNGLIB_MINOR=2
 PNGLIB_RELEASE=15
@@ -21119,7 +21119,7 @@
 # report actual input values of CONFIG_FILES etc. instead of their
 # values after options handling.
 ac_log="
-This file was extended by libpng $as_me 1.2.15rc3, which was
+This file was extended by libpng $as_me 1.2.15rc4, which was
 generated by GNU Autoconf 2.61.  Invocation command line was
 
   CONFIG_FILES    = $CONFIG_FILES
@@ -21172,7 +21172,7 @@
 _ACEOF
 cat >>$CONFIG_STATUS <<_ACEOF
 ac_cs_version="\\
-libpng config.status 1.2.15rc3
+libpng config.status 1.2.15rc4
 configured by $0, generated by GNU Autoconf 2.61,
   with options \\"`echo "$ac_configure_args" | sed 's/^ //; s/[\\""\`\$]/\\\\&/g'`\\"
 
diff --git a/configure.ac b/configure.ac
index e626167..cb5173c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -18,12 +18,12 @@
 
 dnl Version number stuff here:
 
-AC_INIT([libpng], [1.2.15rc3], [png-mng-implement@lists.sourceforge.net])
+AC_INIT([libpng], [1.2.15rc4], [png-mng-implement@lists.sourceforge.net])
 AM_INIT_AUTOMAKE
 dnl stop configure from automagically running automake
 AM_MAINTAINER_MODE
 
-PNGLIB_VERSION=1.2.15rc3
+PNGLIB_VERSION=1.2.15rc4
 PNGLIB_MAJOR=1
 PNGLIB_MINOR=2
 PNGLIB_RELEASE=15
diff --git a/libpng.3 b/libpng.3
index 9943287..43534e5 100644
--- a/libpng.3
+++ b/libpng.3
@@ -1,6 +1,6 @@
-.TH LIBPNG 3 "December 25, 2006"
+.TH LIBPNG 3 "December 27, 2006"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.2.15rc3
+libpng \- Portable Network Graphics (PNG) Reference Library 1.2.15rc4
 .SH SYNOPSIS
 \fB
 #include <png.h>\fP
@@ -410,7 +410,7 @@
 .SH LIBPNG.TXT
 libpng.txt - A description on how to use and modify libpng
 
- libpng version 1.2.15rc3 - December 25, 2006
+ libpng version 1.2.15rc4 - December 27, 2006
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2005 Glenn Randers-Pehrson
@@ -3327,13 +3327,13 @@
 
 .SH IX. Y2K Compliance in libpng
 
-December 25, 2006
+December 27, 2006
 
 Since the PNG Development group is an ad-hoc body, we can't make
 an official declaration.
 
 This is your unofficial assurance that libpng from version 0.71 and
-upward through 1.2.15rc3 are Y2K compliant.  It is my belief that earlier
+upward through 1.2.15rc4 are Y2K compliant.  It is my belief that earlier
 versions were also Y2K compliant.
 
 Libpng only has three year fields.  One is a 2-byte unsigned integer that
@@ -3507,8 +3507,8 @@
  1.0.22rc1           10    10022  10.so.0.22[.0]
  1.2.14rc1           13    10214  12.so.0.14[.0]
  1.2.15beta1-6       13    10215  12.so.0.15[.0]
- 1.0.23rc1-2         10    10023  10.so.0.23[.0]
- 1.2.15rc1-2         13    10215  12.so.0.15[.0]
+ 1.0.23rc1-4         10    10023  10.so.0.23[.0]
+ 1.2.15rc1-4         13    10215  12.so.0.15[.0]
 
 Henceforth the source version will match the shared-library minor
 and patch numbers; the shared-library major version number will be
@@ -3564,7 +3564,7 @@
 
 Thanks to Frank J. T. Wojcik for helping with the documentation.
 
-Libpng version 1.2.15rc3 - December 25, 2006:
+Libpng version 1.2.15rc4 - December 27, 2006:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
 
@@ -3585,7 +3585,7 @@
 If you modify libpng you may insert additional notices immediately following
 this sentence.
 
-libpng versions 1.2.6, August 15, 2004, through 1.2.15rc3, December 25, 2006, are
+libpng versions 1.2.6, August 15, 2004, through 1.2.15rc4, December 27, 2006, are
 Copyright (c) 2004-2006 Glenn Randers-Pehrson, and are
 distributed according to the same disclaimer and license as libpng-1.2.5
 with the following individual added to the list of Contributing Authors
@@ -3684,7 +3684,7 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-December 25, 2006
+December 27, 2006
 
 .\" end of man page
 
diff --git a/libpng.txt b/libpng.txt
index 77c76da..cb71b2e 100644
--- a/libpng.txt
+++ b/libpng.txt
@@ -1,6 +1,6 @@
 libpng.txt - A description on how to use and modify libpng
 
- libpng version 1.2.15rc3 - December 25, 2006
+ libpng version 1.2.15rc4 - December 27, 2006
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2005 Glenn Randers-Pehrson
@@ -2917,13 +2917,13 @@
 
 IX. Y2K Compliance in libpng
 
-December 25, 2006
+December 27, 2006
 
 Since the PNG Development group is an ad-hoc body, we can't make
 an official declaration.
 
 This is your unofficial assurance that libpng from version 0.71 and
-upward through 1.2.15rc3 are Y2K compliant.  It is my belief that earlier
+upward through 1.2.15rc4 are Y2K compliant.  It is my belief that earlier
 versions were also Y2K compliant.
 
 Libpng only has three year fields.  One is a 2-byte unsigned integer that
diff --git a/libpngpf.3 b/libpngpf.3
index ef98623..d440d50 100644
--- a/libpngpf.3
+++ b/libpngpf.3
@@ -1,6 +1,6 @@
-.TH LIBPNGPF 3 "December 25, 2006"
+.TH LIBPNGPF 3 "December 27, 2006"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.2.15rc3
+libpng \- Portable Network Graphics (PNG) Reference Library 1.2.15rc4
 (private functions)
 .SH SYNOPSIS
 \fB#include <png.h>\fP
diff --git a/png.5 b/png.5
index c0cf568..c95683c 100644
--- a/png.5
+++ b/png.5
@@ -1,4 +1,4 @@
-.TH PNG 5 "December 25, 2006"
+.TH PNG 5 "December 27, 2006"
 .SH NAME
 png \- Portable Network Graphics (PNG) format
 .SH DESCRIPTION
diff --git a/png.c b/png.c
index 79936c0..f9fc834 100644
--- a/png.c
+++ b/png.c
@@ -13,7 +13,7 @@
 #include "png.h"
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef version_1_2_15rc3 Your_png_h_is_not_version_1_2_15rc3;
+typedef version_1_2_15rc4 Your_png_h_is_not_version_1_2_15rc4;
 
 /* Version information for C files.  This had better match the version
  * string defined in png.h.  */
@@ -701,7 +701,7 @@
 png_get_copyright(png_structp png_ptr)
 {
    if (&png_ptr != NULL)  /* silence compiler warning about unused png_ptr */
-   return ((png_charp) "\n libpng version 1.2.15rc3 - December 25, 2006\n\
+   return ((png_charp) "\n libpng version 1.2.15rc4 - December 27, 2006\n\
    Copyright (c) 1998-2006 Glenn Randers-Pehrson\n\
    Copyright (c) 1996-1997 Andreas Dilger\n\
    Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.\n");
diff --git a/png.h b/png.h
index 2f35ce5..59606d8 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.2.15rc3 - December 25, 2006
+ * libpng version 1.2.15rc4 - December 27, 2006
  * Copyright (c) 1998-2006 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.)
@@ -9,7 +9,7 @@
  * Authors and maintainers:
  *  libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *  libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- *  libpng versions 0.97, January 1998, through 1.2.15rc3 - December 25, 2006: Glenn
+ *  libpng versions 0.97, January 1998, through 1.2.15rc4 - December 27, 2006: Glenn
  *  See also "Contributing Authors", below.
  *
  * Note about libpng version numbers:
@@ -135,8 +135,8 @@
  *    1.0.22                  10    10022  10.so.0.22[.0]
  *    1.2.14                  13    10214  12.so.0.14[.0]
  *    1.2.15beta1-6           13    10215  12.so.0.15[.0]
- *    1.0.23rc1-2             10    10023  10.so.0.23[.0]
- *    1.2.15rc1-2             13    10215  12.so.0.15[.0]
+ *    1.0.23rc1-4             10    10023  10.so.0.23[.0]
+ *    1.2.15rc1-4             13    10215  12.so.0.15[.0]
  *
  *    Henceforth the source version will match the shared-library major
  *    and minor numbers; the shared-library major version number will be
@@ -166,7 +166,7 @@
  * If you modify libpng you may insert additional notices immediately following
  * this sentence.
  *
- * libpng versions 1.2.6, August 15, 2004, through 1.2.15rc3, December 25, 2006, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.2.15rc4, December 27, 2006, are
  * Copyright (c) 2004, 2006 Glenn Randers-Pehrson, and are
  * distributed according to the same disclaimer and license as libpng-1.2.5
  * with the following individual added to the list of Contributing Authors:
@@ -278,13 +278,13 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    December 25, 2006
+ *    December 27, 2006
  *
  *    Since the PNG Development group is an ad-hoc body, we can't make
  *    an official declaration.
  *
  *    This is your unofficial assurance that libpng from version 0.71 and
- *    upward through 1.2.15rc3 are Y2K compliant.  It is my belief that earlier
+ *    upward through 1.2.15rc4 are Y2K compliant.  It is my belief that earlier
  *    versions were also Y2K compliant.
  *
  *    Libpng only has three year fields.  One is a 2-byte unsigned integer
@@ -340,9 +340,9 @@
  */
 
 /* Version information for png.h - this should match the version in png.c */
-#define PNG_LIBPNG_VER_STRING "1.2.15rc3"
+#define PNG_LIBPNG_VER_STRING "1.2.15rc4"
 #define PNG_HEADER_VERSION_STRING \
-   " libpng version 1.2.15rc3 - December 25, 2006 (header)\n"
+   " libpng version 1.2.15rc4 - December 27, 2006 (header)\n"
 
 #define PNG_LIBPNG_VER_SONUM   0
 #define PNG_LIBPNG_VER_DLLNUM  13
@@ -354,7 +354,7 @@
 /* This should match the numeric part of the final component of
  * PNG_LIBPNG_VER_STRING, omitting any leading zero: */
 
-#define PNG_LIBPNG_VER_BUILD  3
+#define PNG_LIBPNG_VER_BUILD  4
 
 /* Release Status */
 #define PNG_LIBPNG_BUILD_ALPHA    1
@@ -1388,7 +1388,7 @@
 /* This triggers a compiler error in png.c, if png.c and png.h
  * do not agree upon the version number.
  */
-typedef png_structp version_1_2_15rc3;
+typedef png_structp version_1_2_15rc4;
 
 typedef png_struct FAR * FAR * png_structpp;
 
diff --git a/pngconf.h b/pngconf.h
index f3948cc..d0c418e 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.2.15rc3 - December 25, 2006
+ * libpng version 1.2.15rc4 - December 27, 2006
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2005 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
diff --git a/pngrtran.c b/pngrtran.c
index 8f68603..b8d1d92 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -1,7 +1,7 @@
 
 /* pngrtran.c - transforms the data in a row for PNG readers
  *
- * Last changed in libpng 1.2.13 November 13, 2006
+ * Last changed in libpng 1.2.15 December 31, 2006
  * For conditions of distribution and use, see copyright notice in png.h
  * Copyright (c) 1998-2006 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -101,10 +101,16 @@
     * for the current code, which uses PNG_BACKGROUND_IS_GRAY only to
     * decide when to do the png_do_gray_to_rgb() transformation.
     */
-   if ((need_expand && !(png_ptr->color_type & PNG_COLOR_MASK_COLOR)) ||
-       (!need_expand && background_color->red == background_color->green &&
-        background_color->red == background_color->blue))
+   if ((need_expand && !(png_ptr->color_type & PNG_COLOR_MASK_COLOR)))
+   {
       png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+   } else if (!need_expand &&
+              background_color->red == background_color->green &&
+              background_color->red == background_color->blue)
+   {
+      png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
+      png_ptr->background.gray = background_color->red;
+   }
 }
 #endif
 
diff --git a/pngtest.c b/pngtest.c
index 47f4873..6906c45 100644
--- a/pngtest.c
+++ b/pngtest.c
@@ -1547,4 +1547,4 @@
 }
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef version_1_2_15rc3 your_png_h_is_not_version_1_2_15rc3;
+typedef version_1_2_15rc4 your_png_h_is_not_version_1_2_15rc4;
diff --git a/scripts/libpng-config-head.in b/scripts/libpng-config-head.in
index b3b343f..02710df 100755
--- a/scripts/libpng-config-head.in
+++ b/scripts/libpng-config-head.in
@@ -8,7 +8,7 @@
 
 # Modeled after libxml-config.
 
-version=1.2.15rc3
+version=1.2.15rc4
 prefix=""
 libdir=""
 libs=""
diff --git a/scripts/libpng.pc-configure.in b/scripts/libpng.pc-configure.in
index 0a03480..26bd14a 100644
--- a/scripts/libpng.pc-configure.in
+++ b/scripts/libpng.pc-configure.in
@@ -5,6 +5,6 @@
 
 Name: libpng
 Description: Loads and saves PNG files
-Version: 1.2.15rc3
+Version: 1.2.15rc4
 Libs: -L${libdir} -lpng12
 Cflags: -I${includedir} @LIBPNG_NO_MMX@
diff --git a/scripts/libpng.pc.in b/scripts/libpng.pc.in
index a8348a7..03fb3d4 100644
--- a/scripts/libpng.pc.in
+++ b/scripts/libpng.pc.in
@@ -5,6 +5,6 @@
 
 Name: libpng
 Description: Loads and saves PNG files
-Version: 1.2.15rc3
+Version: 1.2.15rc4
 Libs: -L${libdir} -lpng12
 Cflags: -I${includedir}
diff --git a/scripts/makefile.32sunu b/scripts/makefile.32sunu
index 3a0d1d6..0ec5365 100644
--- a/scripts/makefile.32sunu
+++ b/scripts/makefile.32sunu
@@ -8,7 +8,7 @@
 # Library name:
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.64sunu b/scripts/makefile.64sunu
index bd9d5b1..0787d11 100644
--- a/scripts/makefile.64sunu
+++ b/scripts/makefile.64sunu
@@ -8,7 +8,7 @@
 # Library name:
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.aix b/scripts/makefile.aix
index 4ca059d..df64f67 100644
--- a/scripts/makefile.aix
+++ b/scripts/makefile.aix
@@ -20,7 +20,7 @@
 
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 prefix=/usr/local
diff --git a/scripts/makefile.beos b/scripts/makefile.beos
index aca2ddf..595ebf0 100644
--- a/scripts/makefile.beos
+++ b/scripts/makefile.beos
@@ -8,7 +8,7 @@
 # Library name:
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.cygwin b/scripts/makefile.cygwin
index 8bf2488..bf3f9cf 100644
--- a/scripts/makefile.cygwin
+++ b/scripts/makefile.cygwin
@@ -80,7 +80,7 @@
 LIBNAME = libpng12
 PNGMAJ = 0
 CYGDLL = 12
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 SHAREDLIB=cygpng$(CYGDLL).dll
diff --git a/scripts/makefile.darwin b/scripts/makefile.darwin
index 143bbba..c27b892 100644
--- a/scripts/makefile.darwin
+++ b/scripts/makefile.darwin
@@ -19,7 +19,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.dec b/scripts/makefile.dec
index 34f049b..c102bf0 100644
--- a/scripts/makefile.dec
+++ b/scripts/makefile.dec
@@ -5,7 +5,7 @@
 
 # Library name:
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 LIBNAME = libpng12
 
diff --git a/scripts/makefile.elf b/scripts/makefile.elf
index 16f446d..968e61c 100644
--- a/scripts/makefile.elf
+++ b/scripts/makefile.elf
@@ -12,7 +12,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.gcmmx b/scripts/makefile.gcmmx
index befdb84..0a4c257 100644
--- a/scripts/makefile.gcmmx
+++ b/scripts/makefile.gcmmx
@@ -16,7 +16,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.hp64 b/scripts/makefile.hp64
index bcc5c48..a6ca46d 100644
--- a/scripts/makefile.hp64
+++ b/scripts/makefile.hp64
@@ -18,7 +18,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.hpgcc b/scripts/makefile.hpgcc
index 8f2c7b6..9592ebc 100644
--- a/scripts/makefile.hpgcc
+++ b/scripts/makefile.hpgcc
@@ -8,7 +8,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.hpux b/scripts/makefile.hpux
index 6406929..019c53c 100644
--- a/scripts/makefile.hpux
+++ b/scripts/makefile.hpux
@@ -18,7 +18,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.linux b/scripts/makefile.linux
index f02e90a..32695f3 100644
--- a/scripts/makefile.linux
+++ b/scripts/makefile.linux
@@ -6,7 +6,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.mingw b/scripts/makefile.mingw
index aae14b9..c4080eb 100644
--- a/scripts/makefile.mingw
+++ b/scripts/makefile.mingw
@@ -76,7 +76,7 @@
 LIBNAME = libpng12
 PNGMAJ = 0
 MINGDLL = 12
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 SHAREDLIB=libpng$(MINGDLL).dll
diff --git a/scripts/makefile.ne12bsd b/scripts/makefile.ne12bsd
index 72c650c..0e08e29 100644
--- a/scripts/makefile.ne12bsd
+++ b/scripts/makefile.ne12bsd
@@ -13,7 +13,7 @@
 
 LIB=	png12
 SHLIB_MAJOR=	0
-SHLIB_MINOR=	1.2.15rc3
+SHLIB_MINOR=	1.2.15rc4
 SRCS=	pnggccrd.c png.c pngset.c pngget.c pngrutil.c pngtrans.c pngwutil.c \
 		pngread.c pngrio.c pngwio.c pngwrite.c pngrtran.c \
 		pngwtran.c pngmem.c pngerror.c pngpread.c
diff --git a/scripts/makefile.netbsd b/scripts/makefile.netbsd
index 7069bfc..b8d9c07 100644
--- a/scripts/makefile.netbsd
+++ b/scripts/makefile.netbsd
@@ -13,7 +13,7 @@
 
 LIB=	png
 SHLIB_MAJOR=	3
-SHLIB_MINOR=	1.2.15rc3
+SHLIB_MINOR=	1.2.15rc4
 SRCS=	pnggccrd.c png.c pngset.c pngget.c pngrutil.c pngtrans.c pngwutil.c \
 		pngread.c pngrio.c pngwio.c pngwrite.c pngrtran.c \
 		pngwtran.c pngmem.c pngerror.c pngpread.c
diff --git a/scripts/makefile.nommx b/scripts/makefile.nommx
index 7d3f26d..d1ef7ca 100644
--- a/scripts/makefile.nommx
+++ b/scripts/makefile.nommx
@@ -6,7 +6,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.openbsd b/scripts/makefile.openbsd
index 5a0ed23..68624f3 100644
--- a/scripts/makefile.openbsd
+++ b/scripts/makefile.openbsd
@@ -7,7 +7,7 @@
 MANDIR= ${PREFIX}/man/cat
 
 SHLIB_MAJOR=	0
-SHLIB_MINOR=	1.2.15rc3
+SHLIB_MINOR=	1.2.15rc4
 
 LIB=	png
 SRCS=	png.c pngerror.c pnggccrd.c pngget.c pngmem.c pngpread.c \
diff --git a/scripts/makefile.sco b/scripts/makefile.sco
index ef1d84a..5a8016c 100644
--- a/scripts/makefile.sco
+++ b/scripts/makefile.sco
@@ -9,7 +9,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.sggcc b/scripts/makefile.sggcc
index f2eb017..96a661d 100644
--- a/scripts/makefile.sggcc
+++ b/scripts/makefile.sggcc
@@ -6,7 +6,7 @@
 # Library name:
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.sgi b/scripts/makefile.sgi
index fda9c3b..e40d3f0 100644
--- a/scripts/makefile.sgi
+++ b/scripts/makefile.sgi
@@ -6,7 +6,7 @@
 # Library name:
 LIBNAME=libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/makefile.so9 b/scripts/makefile.so9
index 5149da1..e0bd142 100644
--- a/scripts/makefile.so9
+++ b/scripts/makefile.so9
@@ -8,7 +8,7 @@
 
 # Library name:
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 LIBNAME = libpng12
 
diff --git a/scripts/makefile.solaris b/scripts/makefile.solaris
index ceea504..ac11b06 100644
--- a/scripts/makefile.solaris
+++ b/scripts/makefile.solaris
@@ -8,7 +8,7 @@
 # Library name:
 LIBNAME = libpng12
 PNGMAJ = 0
-PNGMIN = 1.2.15rc3
+PNGMIN = 1.2.15rc4
 PNGVER = $(PNGMAJ).$(PNGMIN)
 
 # Shared library names:
diff --git a/scripts/pngos2.def b/scripts/pngos2.def
index 759498a..7a78c18 100644
--- a/scripts/pngos2.def
+++ b/scripts/pngos2.def
@@ -2,7 +2,7 @@
 ; PNG.LIB module definition file for OS/2
 ;----------------------------------------
 
-; Version 1.2.15rc3
+; Version 1.2.15rc4
 
 LIBRARY		PNG
 DESCRIPTION	"PNG image compression library for OS/2"
diff --git a/scripts/pngw32.def b/scripts/pngw32.def
index 2a2f314..e57bed2 100644
--- a/scripts/pngw32.def
+++ b/scripts/pngw32.def
@@ -5,7 +5,7 @@
 LIBRARY
 
 EXPORTS
-;Version 1.2.15rc3
+;Version 1.2.15rc4
   png_build_grayscale_palette  @1
   png_check_sig        @2
   png_chunk_error      @3