diff --git a/ANNOUNCE b/ANNOUNCE
index 51c3a7c..94a3969 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,4 +1,4 @@
-Libpng 1.6.30 - June 28, 2017
+Libpng 1.6.31 - July 27, 2017
 
 This is a public release of libpng, intended for use in production codes.
 
@@ -7,42 +7,51 @@
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   libpng-1.6.30.tar.xz (LZMA-compressed, recommended)
-   libpng-1.6.30.tar.gz
+   libpng-1.6.31.tar.xz (LZMA-compressed, recommended)
+   libpng-1.6.31.tar.gz
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lpng1630.7z  (LZMA-compressed, recommended)
-   lpng1630.zip
+   lpng1631.7z  (LZMA-compressed, recommended)
+   lpng1631.zip
 
 Other information:
 
-   libpng-1.6.30-README.txt
-   libpng-1.6.30-LICENSE.txt
-   libpng-1.6.30-*.asc (armored detached GPG signatures)
+   libpng-1.6.31-README.txt
+   libpng-1.6.31-LICENSE.txt
+   libpng-1.6.31-*.asc (armored detached GPG signatures)
 
-Changes since the last public release (1.6.29):
+Changes since the last public release (1.6.30):
 
-  Added missing "$(CPPFLAGS)" to the compile line for c.pic.o in
-    makefile.linux and makefile.solaris-x86 (Cosmin).
-  Revised documentation of png_get_error_ptr() in the libpng manual.
-  Silence clang -Wcomma and const drop warnings (Viktor Szakats).
-  Update Sourceforge URLs in documentation (https instead of http).
-  Document need to check for integer overflow when allocating a pixel
-    buffer for multiple rows in contrib/gregbook, contrib/pngminus,
-    example.c, and in the manual (suggested by Jaeseung Choi). This
-    is similar to the bug reported against pngquant in CVE-2016-5735.
-  Removed reference to the obsolete PNG_SAFE_LIMITS macro in the documentation.
-  Check for integer overflow in contrib/visupng and contrib/tools/genpng.
-  Do not double evaluate CMAKE_SYSTEM_PROCESSOR in CMakeLists.txt.
-  Test CMAKE_HOST_WIN32 instead of WIN32 in CMakeLists.txt.
-  Fix some URL in documentation.
-  Avoid writing an empty IDAT when the last IDAT exactly fills the
-    compression buffer (bug report by Brian Baird).  This bug was
-    introduced in libpng-1.6.0.
-  Update copyright year in pnglibconf.h, make ltmain.sh executable.
-  Add a reference to the libpng.download site in README.
+  Guard the definition of _POSIX_SOURCE in pngpriv.h (AIX already defines it;
+    bug report by Michael Felt).
+  Revised pngpriv.h to work around failure to compile arm/filter_neon.S
+    ("typedef" directive is unrecognized by the assembler). The problem
+    was introduced in libpng-1.6.30beta01.
+  Added "Requires: zlib" to libpng.pc.in (Pieter Neerincx).
+  Added special case for FreeBSD in arm/filter_neon.S (Maya Rashish).
+  Added instructions for disabling hardware optimizations in INSTALL.
+  Added "--enable-hardware-optimizations" configuration flag to enable
+    or disable all hardware optimizations with one flag.
+  Updated CMakeLists.txt to add INTEL_SSE and MIPS_MSA platforms.
+  Changed "int" to "png_size_t" in intel/filter_sse2.c to prevent
+    possible integer overflow (Bug report by John Bowler).
+  Quieted "declaration after statement" warnings in intel/filter_sse2.c.
+  Added scripts/makefile-linux-opt, which has hardware optimizations enabled.
+  Removed one of the GCC-7.1.0 'strict-overflow' warnings that result when
+    integers appear on both sides of a compare.  Worked around the others by
+    forcing the strict-overflow setting in the relevant functions to a level
+    where they are not reported (John Bowler).
+  Changed "FALL THROUGH" comments to "FALLTHROUGH" because GCC doesn't like
+    the space.
+  Worked around some C-style casts from (void*) because g++ 5.4.0 objects
+    to them.
+  Increased the buffer size for 'sprint' to pass the gcc 7.1.0 'sprint
+    overflow' check that is on by default with -Wall -Wextra.
+  Added eXIf chunk support.
+  Added a minimal eXIf chunk (with Orientation and FocalLengthIn35mmFilm
+    tags) to pngtest.png.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index b8e0f97..a2f367a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5855,6 +5855,59 @@
 Version 1.6.30 [June 28, 2017]
   No changes.
 
+Version 1.6.31beta01 [July 5, 2017]
+  Guard the definition of _POSIX_SOURCE in pngpriv.h (AIX already defines it;
+    bug report by Michael Felt).
+  Revised pngpriv.h to work around failure to compile arm/filter_neon.S
+    ("typedef" directive is unrecognized by the assembler). The problem
+    was introduced in libpng-1.6.30beta01.
+  Added "Requires: zlib" to libpng.pc.in (Pieter Neerincx).
+  Added special case for FreeBSD in arm/filter_neon.S (Maya Rashish).
+
+Version 1.6.31beta02 [July 8, 2017]
+  Added instructions for disabling hardware optimizations in INSTALL.
+  Added "--enable-hardware-optimizations" configuration flag to enable
+    or disable all hardware optimizations with one flag.
+
+Version 1.6.31beta03 [July 9, 2017]
+  Updated CMakeLists.txt to add INTEL_SSE and MIPS_MSA platforms.
+  Changed "int" to "png_size_t" in intel/filter_sse2.c to prevent
+    possible integer overflow (Bug report by John Bowler).
+  Quieted "declaration after statement" warnings in intel/filter_sse2.c.
+  Added scripts/makefile-linux-opt, which has hardware optimizations enabled.
+
+Version 1.6.31beta04 [July 11, 2017]
+  Removed one of the GCC-7.1.0 'strict-overflow' warnings that result when
+    integers appear on both sides of a compare.  Worked around the others by
+    forcing the strict-overflow setting in the relevant functions to a level
+    where they are not reported (John Bowler).
+  Changed "FALL THROUGH" comments to "FALLTHROUGH" because GCC doesn't like
+    the space.
+  Worked around some C-style casts from (void*) because g++ 5.4.0 objects
+    to them.
+  Increased the buffer size for 'sprint' to pass the gcc 7.1.0 'sprint
+    overflow' check that is on by default with -Wall -Wextra.
+
+Version 1.6.31beta05 [July 13, 2017]
+  Added eXIf chunk support.
+
+Version 1.6.31beta06 [July 17, 2017]
+  Added a minimal eXIf chunk (with Orientation and FocalLengthIn35mmFilm
+    tags) to pngtest.png.
+
+Version 1.6.31beta07 [July 18, 2017]
+  Revised the eXIf chunk in pngtest.png to fix "Bad IFD1 Directory" warning.
+
+Version 1.6.31rc01 [July 19, 2017]
+  No changes.
+
+Version 1.6.31rc02 [July 25, 2017]
+  Fixed typo in example.c (png_free_image should be png_image_free) (Bug
+    report by John Smith)
+
+Version 1.6.31 [July 27, 2017]
+  No changes.
+
 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/CMakeLists.txt b/CMakeLists.txt
index 739ce15..0c72c36 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 # CMakeLists.txt
 
-# Copyright (C) 2007,2009-2016 Glenn Randers-Pehrson
+# Copyright (C) 2007,2009-2017 Glenn Randers-Pehrson
 # Written by Christian Ehrlicher, 2007
 # Revised by Roger Lowman, 2009-2010
 # Revised by Clifford Yapp, 2011-2012
@@ -36,7 +36,7 @@
 
 set(PNGLIB_MAJOR 1)
 set(PNGLIB_MINOR 6)
-set(PNGLIB_RELEASE 30)
+set(PNGLIB_RELEASE 31)
 set(PNGLIB_NAME libpng${PNGLIB_MAJOR}${PNGLIB_MINOR})
 set(PNGLIB_VERSION ${PNGLIB_MAJOR}.${PNGLIB_MINOR}.${PNGLIB_RELEASE})
 
@@ -76,9 +76,13 @@
 option(PNG_DEBUG     "Build with debug output" OFF)
 option(PNGARG        "Disable ANSI-C prototypes" OFF)
 
+option(PNG_HARDWARE_OPTIMIZATIONS "Enable Hardware Optimizations" ON)
+
+
 set(PNG_PREFIX "" CACHE STRING "Prefix to add to the API function names")
 set(DFA_XTRA "" CACHE FILEPATH "File containing extra configuration settings")
 
+if(PNG_HARDWARE_OPTIMIZATIONS)
 # set definitions and sources for arm
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "^arm" OR
   CMAKE_SYSTEM_PROCESSOR MATCHES "^aarch64")
@@ -112,11 +116,9 @@
 # set definitions and sources for powerpc
 if(CMAKE_SYSTEM_PROCESSOR MATCHES "^powerpc*" OR
 	CMAKE_SYSTEM_PROCESSOR MATCHES "^ppc64*" )
-  set(PNG_POWERPC_VSX_POSSIBLE_VALUES check on off)
-  set(PNG_POWERPC_VSX "check" CACHE STRING "Enable POWERPC VSX optimizations:
-     check: (default) use internal checking code;
-     off: disable the optimizations;
-     on: turn on unconditionally.")
+  set(PNG_POWERPC_VSX_POSSIBLE_VALUES on off)
+  set(PNG_POWERPC_VSX "on" CACHE STRING "Enable POWERPC VSX optimizations:
+     off: disable the optimizations.")
   set_property(CACHE PNG_POWERPC_VSX PROPERTY STRINGS
      ${PNG_POWERPC_VSX_POSSIBLE_VALUES})
   list(FIND PNG_POWERPC_VSX_POSSIBLE_VALUES ${PNG_POWERPC_VSX} index)
@@ -127,19 +129,62 @@
     set(libpng_powerpc_sources
       powerpc/powerpc_init.c
       powerpc/filter_vsx_intrinsics.c)
-
     if(${PNG_POWERPC_VSX} STREQUAL "on")
       add_definitions(-DPNG_POWERPC_VSX_OPT=2)
-    elseif(${PNG_POWERPC_VSX} STREQUAL "check")
-      add_definitions(-DPNG_POWERPC_VSX_CHECK_SUPPORTED)
-      message(WARNING
-      "[PNG_POWERPC_VSX==check] Please check contrib/powerpc/README file for the list of supported OSes.")
     endif()
   else()
     add_definitions(-DPNG_POWERPC_VSX_OPT=0)
   endif()
 endif()
 
+# set definitions and sources for intel
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "^i?86" OR
+	CMAKE_SYSTEM_PROCESSOR MATCHES "^x86_64*" )
+  set(PNG_INTEL_SSE_POSSIBLE_VALUES on off)
+  set(PNG_INTEL_SSE "on" CACHE STRING "Enable INTEL_SSE optimizations:
+     off: disable the optimizations")
+  set_property(CACHE PNG_INTEL_SSE PROPERTY STRINGS
+     ${PNG_INTEL_SSE_POSSIBLE_VALUES})
+  list(FIND PNG_INTEL_SSE_POSSIBLE_VALUES ${PNG_INTEL_SSE} index)
+  if(index EQUAL -1)
+    message(FATAL_ERROR
+      " PNG_INTEL_SSE must be one of [${PNG_INTEL_SSE_POSSIBLE_VALUES}]")
+  elseif(NOT ${PNG_INTEL_SSE} STREQUAL "no")
+    set(libpng_intel_sources
+      intel/intel_init.c
+      intel/filter_sse2_intrinsics.c)
+    if(${PNG_INTEL_SSE} STREQUAL "on")
+      add_definitions(-DPNG_INTEL_SSE_OPT=1)
+    endif()
+  else()
+    add_definitions(-DPNG_INTEL_SSE_OPT=0)
+  endif()
+endif()
+
+# set definitions and sources for MIPS
+if(CMAKE_SYSTEM_PROCESSOR MATCHES "mipsel*" OR
+	CMAKE_SYSTEM_PROCESSOR MATCHES "mips64el*" )
+  set(PNG_MIPS_MSA_POSSIBLE_VALUES on off)
+  set(PNG_MIPS_MSA "on" CACHE STRING "Enable MIPS_MSA optimizations:
+     off: disable the optimizations")
+  set_property(CACHE PNG_MIPS_MSA PROPERTY STRINGS
+     ${PNG_MIPS_MSA_POSSIBLE_VALUES})
+  list(FIND PNG_MIPS_MSA_POSSIBLE_VALUES ${PNG_MIPS_MSA} index)
+  if(index EQUAL -1)
+    message(FATAL_ERROR
+      " PNG_MIPS_MSA must be one of [${PNG_MIPS_MSA_POSSIBLE_VALUES}]")
+  elseif(NOT ${PNG_MIPS_MSA} STREQUAL "no")
+    set(libpng_mips_sources
+      mips/mips_init.c
+      mips/filter_msa_intrinsics.c)
+    if(${PNG_MIPS_MSA} STREQUAL "on")
+      add_definitions(-DPNG_MIPS_MSA_OPT=2)
+    endif()
+  else()
+    add_definitions(-DPNG_MIPS_MSA_OPT=0)
+  endif()
+endif()
+endif(PNG_HARDWARE_OPTIMIZATIONS)
 
 # SET LIBNAME
 set(PNG_LIB_NAME png${PNGLIB_MAJOR}${PNGLIB_MINOR})
@@ -432,6 +477,8 @@
   pngwtran.c
   pngwutil.c
   ${libpng_arm_sources}
+  ${libpng_intel_sources}
+  ${libpng_mips_sources}
   ${libpng_powerpc_sources}
 )
 set(pngtest_sources
@@ -726,12 +773,12 @@
         DEPENDS ${PNG_LIB_TARGETS}
         )
     ADD_CUSTOM_TARGET(${DEST_FILE}_COPY ALL DEPENDS ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/${DEST_FILE})
-  else(WIN32 AND NOT CYGWIN AND NOT MSYS)
+  else(CMAKE_HOST_WIN32 AND NOT CYGWIN AND NOT MSYS)
     get_filename_component(LINK_TARGET "${SRC_FILE}" NAME)
     execute_process(COMMAND ${CMAKE_COMMAND} -E make_directory ${CMAKE_CURRENT_BINARY_DIR}/${CMAKE_LIBRARY_OUTPUT_DIRECTORY})
     execute_process(COMMAND ${CMAKE_COMMAND} -E create_symlink "${LINK_TARGET}" ${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/${DEST_FILE} WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
     execute_process(COMMAND ${CMAKE_COMMAND} -E create_symlink "${LINK_TARGET}" ${DEST_FILE} WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR})
-  endif(WIN32 AND NOT CYGWIN AND NOT MSYS)
+  endif(CMAKE_HOST_WIN32 AND NOT CYGWIN AND NOT MSYS)
 endmacro()
 
 # Create source generation scripts.
@@ -770,7 +817,7 @@
 # SET UP LINKS
 if(PNG_SHARED)
   set_target_properties(png PROPERTIES
-#   VERSION 16.${PNGLIB_RELEASE}.1.6.30
+#   VERSION 16.${PNGLIB_RELEASE}.1.6.31
     VERSION 16.${PNGLIB_RELEASE}.0
     SOVERSION 16
     CLEAN_DIRECT_OUTPUT 1)
@@ -855,7 +902,7 @@
             DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)
     install(PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/${PNGLIB_NAME}-config
             DESTINATION bin)
-  endif(NOT WIN32 OR CYGWIN OR MINGW)
+  endif(NOT CMAKE_HOST_WIN32 OR CYGWIN OR MINGW)
 endif()
 
 # On versions of CMake that support it, create an export file CMake
diff --git a/INSTALL b/INSTALL
index 48b1250..e8edb72 100644
--- a/INSTALL
+++ b/INSTALL
@@ -16,10 +16,11 @@
       XI. Prepending a prefix to exported symbols
      XII. Configuring for compiler xxx:
     XIII. Removing unwanted object code
-     XIV. Changes to the build and configuration of libpng in libpng-1.5.x
-      XV. Setjmp/longjmp issues
-     XVI. Common linking failures
-    XVII. Other sources of information about libpng
+     XIV. Enabling or disabling hardware optimizations
+      XV. Changes to the build and configuration of libpng in libpng-1.5.x
+     XVI. Setjmp/longjmp issues
+    XVII. Common linking failures
+   XVIII. Other sources of information about libpng
 
 I. Simple installation
 
@@ -281,7 +282,57 @@
 The size of the library itself should not be an issue, because only
 those sections that are actually used will be loaded into memory.
 
-XIV. Changes to the build and configuration of libpng in libpng-1.5.x
+XIV. Enabling or disabling hardware optimizations
+
+Certain hardware capabilites, such as the Intel SSE instructions,
+are normally detected at run time. Enable them with configure options
+such as one of
+
+   --enable-arm-neon=yes
+   --enable-mips-msa=yes
+   --enable-intel-sse=yes
+   --enable-powerpc-vsx=yes
+
+or enable them all at once with
+
+   --enable-hardware-optimizations=yes
+
+or, if you are not using "configure", you can use one
+or more of
+
+   CPPFLAGS += "-DPNG_ARM_NEON"
+   CPPFLAGS += "-DPNG_MIPS_MSA"
+   CPPFLAGS += "-DPNG_INTEL_SSE"
+   CPPFLAGS += "-DPNG_POWERPC_VSX"
+
+See for example scripts/makefile.linux-opt
+
+If you wish to avoid using them,
+you can disable them via the configure option
+
+   --disable-hardware-optimizations
+
+to disable them all, or
+
+   --enable-intel-sse=no
+
+to disable a particular one,
+or via compiler-command options such as
+
+   CPPFLAGS += "-DPNG_ARM_NEON_OPT=0, -DPNG_MIPS_MSA_OPT=0,
+   -DPNG_INTEL_SSE_OPT=0, -DPNG_POWERPC_VSX_OPT=0"
+
+If you are using cmake, hardware optimizations are "on"
+by default. To disable them, use
+
+    cmake . -DPNG_ARM_NEON=no -DPNG_INTEL_SSE=no \
+            -DPNG_MIPS_MSA=no -DPNG_POWERPC_VSX=no
+
+or disable them all at once with
+
+    cmake . -DPNG_HARDWARE_OPTIMIZATIONS=no
+
+XV. Changes to the build and configuration of libpng in libpng-1.5.x
 
 Details of internal changes to the library code can be found in the CHANGES
 file and in the GIT repository logs.  These will be of no concern to the vast
@@ -372,7 +423,7 @@
 libpng, because than the settings would not accurately reflect the settings
 that were used to build libpng.
 
-XV. Setjmp/longjmp issues
+XVI. Setjmp/longjmp issues
 
 Libpng uses setjmp()/longjmp() for error handling.  Unfortunately setjmp()
 is known to be not thread-safe on some platforms and we don't know of
@@ -390,7 +441,7 @@
 with PNG_SETJMP_SUPPORTED defined, or with PNG_SIMPLIFIED_READ_SUPPORTED
 and PNG_SIMPLIFIED_WRITE_SUPPORTED undefined.
 
-XVI. Common linking failures
+XVII. Common linking failures
 
 If your application fails to find libpng or zlib entries while linking:
 
@@ -402,7 +453,7 @@
   If you are using the vstudio project, observe the WARNING in
   project/vstudio/README.txt.
 
-XVII. Other sources of information about libpng:
+XVIII. Other sources of information about libpng:
 
 Further information can be found in the README and libpng-manual.txt
 files, in the individual makefiles, in png.h, and the manual pages
diff --git a/LICENSE b/LICENSE
index 9e93578..1df0cbb 100644
--- a/LICENSE
+++ b/LICENSE
@@ -10,7 +10,7 @@
 
 This code is released under the libpng license.
 
-libpng versions 1.0.7, July 1, 2000 through 1.6.30, June 28, 2017 are
+libpng versions 1.0.7, July 1, 2000 through 1.6.31, July 27, 2017 are
 Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
 derived from libpng-1.0.6, and are distributed according to the same
 disclaimer and license as libpng-1.0.6 with the following individuals
diff --git a/README b/README
index 65dccaf..1f68cfa 100644
--- a/README
+++ b/README
@@ -1,4 +1,4 @@
-README for libpng version 1.6.30 - June 28, 2017 (shared library 16.0)
+README for libpng version 1.6.31 - July 27, 2017 (shared library 16.0)
 See the note about version numbers near the top of png.h
 
 See INSTALL for instructions on how to install libpng.
diff --git a/arm/filter_neon.S b/arm/filter_neon.S
index 3b061d6..000764c 100644
--- a/arm/filter_neon.S
+++ b/arm/filter_neon.S
@@ -1,9 +1,9 @@
 
 /* filter_neon.S - NEON optimised filter functions
  *
- * Copyright (c) 2014 Glenn Randers-Pehrson
+ * Copyright (c) 2014,2017 Glenn Randers-Pehrson
  * Written by Mans Rullgard, 2011.
- * Last changed in libpng 1.6.16 [December 22, 2014]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -16,7 +16,7 @@
 #define PNG_VERSION_INFO_ONLY
 #include "../pngpriv.h"
 
-#if defined(__linux__) && defined(__ELF__)
+#if (defined(__linux__) || defined(__FreeBSD__)) && defined(__ELF__)
 .section .note.GNU-stack,"",%progbits /* mark stack as non-executable */
 #endif
 
diff --git a/configure.ac b/configure.ac
index 706dbf1..b1fd158 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,7 +25,7 @@
 
 dnl Version number stuff here:
 
-AC_INIT([libpng],[1.6.30],[png-mng-implement@lists.sourceforge.net])
+AC_INIT([libpng],[1.6.31],[png-mng-implement@lists.sourceforge.net])
 AC_CONFIG_MACRO_DIR([scripts])
 
 # libpng does not follow GNU file name conventions (hence 'foreign')
@@ -46,10 +46,10 @@
 dnl AM_PREREQ([1.11.2])
 dnl stop configure from automagically running automake
 
-PNGLIB_VERSION=1.6.30
+PNGLIB_VERSION=1.6.31
 PNGLIB_MAJOR=1
 PNGLIB_MINOR=6
-PNGLIB_RELEASE=30
+PNGLIB_RELEASE=31
 
 dnl End of version number stuff
 
@@ -300,6 +300,55 @@
 # HOST SPECIFIC OPTIONS
 # =====================
 #
+# DEFAULT
+# =======
+#
+AC_ARG_ENABLE([hardware-optimizations],
+   AS_HELP_STRING([[[--enable-hardware-optimizations]]],
+      [Enable hardware optimizations: =no/off, yes/on:]),
+   [case "$enableval" in
+      no|off)
+         # disable hardware optimization on all systems:
+         enable_arm_neon=no
+         AC_DEFINE([PNG_ARM_NEON_OPT], [0],
+           [Disable ARM_NEON optimizations])
+         enable_mips_msa=no
+         AC_DEFINE([PNG_MIPS_MSA_OPT], [0],
+           [Disable MIPS_MSA optimizations])
+         enable_powerpc_vsx=no
+         AC_DEFINE([PNG_POWERPC_VSX_OPT], [0],
+           [Disable POWERPC VSX optimizations])
+         enable_intel_sse=no
+         AC_DEFINE([PNG_INTEL_SSE_OPT], [0],
+           [Disable INTEL_SSE optimizations])
+         ;;
+      *)
+         # allow enabling hardware optimization on any system:
+         case "$host_cpu" in
+            arm*|aarch64*)
+              enable_arm_neon=yes
+              AC_DEFINE([PNG_ARM_NEON_OPT], [0],
+                [Enable ARM_NEON optimizations])
+              ;;
+            mipsel*|mips64el*)
+              enable_mips_msa=yes
+              AC_DEFINE([PNG_MIPS_MSA_OPT], [0],
+                [Enable MIPS_MSA optimizations])
+              ;;
+            i?86|x86_64)
+              enable_intel_sse=yes
+              AC_DEFINE([PNG_INTEL_SSE_OPT], [1],
+                [Enable Intel SSE optimizations])
+              ;;
+            powerpc*|ppc64*)
+              enable_powerpc_vsx=yes
+              AC_DEFINE([PNG_POWERPC_VSX_OPT], [2],
+                [Enable POWERPC VSX optimizations])
+              ;;
+         esac
+         ;;
+   esac])
+
 # ARM
 # ===
 #
diff --git a/contrib/arm-neon/linux.c b/contrib/arm-neon/linux.c
index 94f9bb1..a9bc360 100644
--- a/contrib/arm-neon/linux.c
+++ b/contrib/arm-neon/linux.c
@@ -1,8 +1,8 @@
 /* contrib/arm-neon/linux.c
  *
- * Copyright (c) 2014 Glenn Randers-Pehrson
- * Written by John Bowler, 2014.
- * Last changed in libpng 1.6.16 [December 22, 2014]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 2014, 2017 Glenn Randers-Pehrson
+ * Written by John Bowler, 2014, 2017.
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -62,7 +62,7 @@
 
                counter=0;
                state = Feature;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case Feature:
                /* Match 'FEATURE', ASCII case insensitive. */
@@ -75,7 +75,7 @@
 
                /* did not match 'feature' */
                state = SkipLine;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case SkipLine:
             skipLine:
@@ -110,7 +110,7 @@
 
                state = Neon;
                counter = 0;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case Neon:
                /* Look for 'neon' tag */
@@ -122,7 +122,7 @@
                }
 
                state = SkipTag;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case SkipTag:
                /* Skip non-space characters */
diff --git a/contrib/libtests/pngstest.c b/contrib/libtests/pngstest.c
index 30f57a9..0617dbb 100644
--- a/contrib/libtests/pngstest.c
+++ b/contrib/libtests/pngstest.c
@@ -1,9 +1,8 @@
 /*-
  * pngstest.c
  *
- * Copyright (c) 2013-2016 John Cunningham Bowler
- *
- * Last changed in libpng 1.6.24 [August 4, 2016]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 2013-2017 John Cunningham Bowler
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -2746,22 +2745,27 @@
        */
       else if ((a->opts & ACCUMULATE) == 0)
       {
+#        ifdef __GNUC__
+#           define BYTE_CHARS 20 /* 2^32: GCC sprintf warning */
+#        else
+#           define BYTE_CHARS 3 /* 2^8: real maximum value */
+#        endif
          /* Check the original image first,
           * TODO: deal with input images with bad pixel values?
           */
          if (amax >= a->image.colormap_entries)
          {
-            char pindex[9];
-            sprintf(pindex, "%d[%lu]", amax,
-               (unsigned long)a->image.colormap_entries);
+            char pindex[3+2*BYTE_CHARS];
+            sprintf(pindex, "%d[%u]", amax,
+               (png_byte)/*SAFE*/a->image.colormap_entries);
             return logerror(a, a->file_name, ": bad pixel index: ", pindex);
          }
 
          else if (bmax >= b->image.colormap_entries)
          {
-            char pindex[9];
-            sprintf(pindex, "%d[%lu]", bmax,
-               (unsigned long)b->image.colormap_entries);
+            char pindex[3+2*BYTE_CHARS];
+            sprintf(pindex, "%d[%u]", bmax,
+               (png_byte)/*SAFE*/b->image.colormap_entries);
             return logerror(b, b->file_name, ": bad pixel index: ", pindex);
          }
       }
@@ -2881,10 +2885,13 @@
                {
                   case 4:
                      if (pua[btoa[3]] != pub[3]) break;
+                     /* FALLTHROUGH */
                   case 3:
                      if (pua[btoa[2]] != pub[2]) break;
+                     /* FALLTHROUGH */
                   case 2:
                      if (pua[btoa[1]] != pub[1]) break;
+                     /* FALLTHROUGH */
                   case 1:
                      if (pua[btoa[0]] != pub[0]) break;
                      if (alpha_added != 4 && pub[alpha_added] != 65535) break;
@@ -2900,10 +2907,13 @@
                {
                   case 4:
                      if (psa[btoa[3]] != psb[3]) break;
+                     /* FALLTHROUGH */
                   case 3:
                      if (psa[btoa[2]] != psb[2]) break;
+                     /* FALLTHROUGH */
                   case 2:
                      if (psa[btoa[1]] != psb[1]) break;
+                     /* FALLTHROUGH */
                   case 1:
                      if (psa[btoa[0]] != psb[0]) break;
                      if (alpha_added != 4 && psb[alpha_added] != 255) break;
diff --git a/contrib/libtests/pngunknown.c b/contrib/libtests/pngunknown.c
index aba605e..7bb33f8 100644
--- a/contrib/libtests/pngunknown.c
+++ b/contrib/libtests/pngunknown.c
@@ -1,8 +1,8 @@
 
 /* pngunknown.c - test the read side unknown chunk handling
  *
- * Last changed in libpng 1.6.26 [October 20, 2016]
- * Copyright (c) 2015,2016 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 2015,2017 Glenn Randers-Pehrson
  * Written by John Cunningham Bowler
  *
  * This code is released under the libpng license.
@@ -614,7 +614,7 @@
                   ++(d->error_count);
                   break;
                }
-               /* FALL THROUGH (safe) */
+               /* FALLTHROUGH */ /* (safe) */
             case PNG_HANDLE_CHUNK_ALWAYS:
                break;
          }
diff --git a/contrib/libtests/pngvalid.c b/contrib/libtests/pngvalid.c
index b0daa18..4dc4f84 100644
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -1,7 +1,7 @@
 
 /* pngvalid.c - validate libpng by constructing then reading png files.
  *
- * Last changed in libpng 1.6.29 [March 16, 2017]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  * Copyright (c) 2014-2017 John Cunningham Bowler
  *
  * This code is released under the libpng license.
@@ -6584,16 +6584,16 @@
    {
    case PNG_COLOR_TYPE_PALETTE:
       if (dp->output_bit_depth > 8) goto error;
-      /*FALL THROUGH*/
+      /* FALLTHROUGH */
    case PNG_COLOR_TYPE_GRAY:
       if (dp->output_bit_depth == 1 || dp->output_bit_depth == 2 ||
          dp->output_bit_depth == 4)
          break;
-      /*FALL THROUGH*/
+      /* FALLTHROUGH */
    default:
       if (dp->output_bit_depth == 8 || dp->output_bit_depth == 16)
          break;
-      /*FALL THROUGH*/
+      /* FALLTHROUGH */
    error:
       {
          char message[128];
@@ -9994,9 +9994,9 @@
                case PNG_BACKGROUND_GAMMA_FILE:
                case PNG_BACKGROUND_GAMMA_UNIQUE:
                   use_background = (alpha >= 0 && alpha < 1);
-                  /*FALL THROUGH*/
 #           endif
 #           ifdef PNG_READ_ALPHA_MODE_SUPPORTED
+               /* FALLTHROUGH */
                case ALPHA_MODE_OFFSET + PNG_ALPHA_STANDARD:
                case ALPHA_MODE_OFFSET + PNG_ALPHA_BROKEN:
                case ALPHA_MODE_OFFSET + PNG_ALPHA_OPTIMIZED:
diff --git a/contrib/testpngs/makepngs.sh b/contrib/testpngs/makepngs.sh
index 8187587..059503e 100755
--- a/contrib/testpngs/makepngs.sh
+++ b/contrib/testpngs/makepngs.sh
@@ -5,7 +5,7 @@
 
 # Copyright (c) 2015 John Cunningham Bowler
 
-# Last changed in libpng 1.7.0 [(PENDING RELEASE)]
+# Last changed in libpng 1.6.20 [December 3, 2015]
 
 # This code is released under the libpng license.
 # For conditions of distribution and use, see the disclaimer
diff --git a/contrib/tools/pngfix.c b/contrib/tools/pngfix.c
index 6da970c..69ffc17 100644
--- a/contrib/tools/pngfix.c
+++ b/contrib/tools/pngfix.c
@@ -1,8 +1,7 @@
 /* pngfix.c
  *
- * Copyright (c) 2014-2016 John Cunningham Bowler
- *
- * Last changed in libpng 1.6.26 [October 20, 2016]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 2014-2017 John Cunningham Bowler
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -2416,7 +2415,7 @@
                   endrc = ZLIB_TOO_FAR_BACK;
                   break;
                }
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             default:
                zlib_message(zlib, 0/*stream error*/);
@@ -2570,7 +2569,7 @@
                   list->lengths[i] -= zlib->extra_bytes;
                   list->count = i+1;
                   zlib->idat->idat_list_tail = list;
-                  /* FALL THROUGH */
+                  /* FALLTHROUGH */
 
                default:
                   return rc;
@@ -2673,7 +2672,7 @@
             /* Truncated stream; unrecoverable, gets converted to ZLIB_FATAL */
             zlib.z.msg = PNGZ_MSG_CAST("[truncated]");
             zlib_message(&zlib, 0/*expected*/);
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
 
          default:
             /* Unrecoverable error; skip the chunk; a zlib_message has already
@@ -3341,7 +3340,7 @@
                if (file->state != STATE_IDAT && length > 0)
                   setpos(chunk);
             }
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
 
          default:
             assert(chunk != NULL);
diff --git a/example.c b/example.c
index a71000f..99d2f05 100644
--- a/example.c
+++ b/example.c
@@ -114,13 +114,13 @@
 
          else
          {
-            /* Calling png_free_image is optional unless the simplified API was
+            /* Calling png_image_free is optional unless the simplified API was
              * not run to completion.  In this case if there wasn't enough
              * memory for 'buffer' we didn't complete the read, so we must free
              * the image:
              */
             if (buffer == NULL)
-               png_free_image(&image);
+               png_image_free(&image);
 
             else
                free(buffer);
diff --git a/intel/filter_sse2_intrinsics.c b/intel/filter_sse2_intrinsics.c
index b91d8da..5e8553f 100644
--- a/intel/filter_sse2_intrinsics.c
+++ b/intel/filter_sse2_intrinsics.c
@@ -5,7 +5,7 @@
  * Written by Mike Klein and Matt Sarett
  * Derived from arm/filter_neon_intrinsics.c
  *
- * Last changed in libpng 1.6.29 [March 16, 2017]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -40,7 +40,7 @@
    /* We'll load 2 bytes, then 1 byte,
     * then mask them together, and finally load into SSE.
     */
-   const png_uint_16* p01 = p;
+   const png_uint_16* p01 = (png_const_uint_16p)p;
    const png_byte*    p2  = (const png_byte*)(p01+1);
 
    png_uint_32 v012 = (png_uint_32)(*p01)
@@ -53,12 +53,15 @@
     * its bottom two bytes, then its third byte.
     */
    png_uint_32 v012;
+   png_uint_16* p01;
+   png_byte*    p2;
+
    store4(&v012, v);
 
-   png_uint_16* p01 = p;
-   png_byte*    p2  = (png_byte*)(p01+1);
-   *p01 = v012;
-   *p2  = v012 >> 16;
+   p01 = (png_uint_16p)p;
+   p2  = (png_byte*)(p01+1);
+   *p01 = (png_uint_16)v012;
+   *p2  = (png_byte)(v012 >> 16);
 }
 
 void png_read_filter_row_sub3_sse2(png_row_infop row_info, png_bytep row,
@@ -68,10 +71,13 @@
     * There is no pixel to the left of the first pixel.  It's encoded directly.
     * That works with our main loop if we just say that left pixel was zero.
     */
-   png_debug(1, "in png_read_filter_row_sub3_sse2");
+   png_size_t rb;
+
    __m128i a, d = _mm_setzero_si128();
 
-   int rb = row_info->rowbytes;
+   png_debug(1, "in png_read_filter_row_sub3_sse2");
+
+   rb = row_info->rowbytes;
    while (rb >= 4) {
       a = d; d = load4(row);
       d = _mm_add_epi8(d, a);
@@ -88,6 +94,7 @@
       row += 3;
       rb  -= 3;
    }
+   PNG_UNUSED(prev)
 }
 
 void png_read_filter_row_sub4_sse2(png_row_infop row_info, png_bytep row,
@@ -97,11 +104,14 @@
     * There is no pixel to the left of the first pixel.  It's encoded directly.
     * That works with our main loop if we just say that left pixel was zero.
     */
-   png_debug(1, "in png_read_filter_row_sub4_sse2");
+   png_size_t rb;
+
    __m128i a, d = _mm_setzero_si128();
 
-   int rb = row_info->rowbytes;
-   while (rb > 0) {
+   png_debug(1, "in png_read_filter_row_sub4_sse2");
+
+   rb = row_info->rowbytes+4;
+   while (rb > 4) {
       a = d; d = load4(row);
       d = _mm_add_epi8(d, a);
       store4(row, d);
@@ -109,6 +119,7 @@
       row += 4;
       rb  -= 4;
    }
+   PNG_UNUSED(prev)
 }
 
 void png_read_filter_row_avg3_sse2(png_row_infop row_info, png_bytep row,
@@ -119,18 +130,23 @@
     * predicted to be half of the pixel above it.  So again, this works
     * perfectly with our loop if we make sure a starts at zero.
     */
-   png_debug(1, "in png_read_filter_row_avg3_sse2");
+
+   png_size_t rb;
+
    const __m128i zero = _mm_setzero_si128();
+
    __m128i    b;
    __m128i a, d = zero;
 
-   int rb = row_info->rowbytes;
+   png_debug(1, "in png_read_filter_row_avg3_sse2");
+   rb = row_info->rowbytes;
    while (rb >= 4) {
+      __m128i avg;
              b = load4(prev);
       a = d; d = load4(row );
 
       /* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
-      __m128i avg = _mm_avg_epu8(a,b);
+      avg = _mm_avg_epu8(a,b);
       /* ...but we can fix it up by subtracting off 1 if it rounded up. */
       avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
                                             _mm_set1_epi8(1)));
@@ -142,11 +158,12 @@
       rb   -= 3;
    }
    if (rb > 0) {
+      __m128i avg;
              b = load3(prev);
       a = d; d = load3(row );
 
       /* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
-      __m128i avg = _mm_avg_epu8(a,b);
+      avg = _mm_avg_epu8(a,b);
       /* ...but we can fix it up by subtracting off 1 if it rounded up. */
       avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
                                             _mm_set1_epi8(1)));
@@ -168,18 +185,21 @@
     * predicted to be half of the pixel above it.  So again, this works
     * perfectly with our loop if we make sure a starts at zero.
     */
-   png_debug(1, "in png_read_filter_row_avg4_sse2");
+   png_size_t rb;
    const __m128i zero = _mm_setzero_si128();
    __m128i    b;
    __m128i a, d = zero;
 
-   int rb = row_info->rowbytes;
-   while (rb > 0) {
+   png_debug(1, "in png_read_filter_row_avg4_sse2");
+
+   rb = row_info->rowbytes+4;
+   while (rb > 4) {
+      __m128i avg;
              b = load4(prev);
       a = d; d = load4(row );
 
       /* PNG requires a truncating average, so we can't just use _mm_avg_epu8 */
-      __m128i avg = _mm_avg_epu8(a,b);
+      avg = _mm_avg_epu8(a,b);
       /* ...but we can fix it up by subtracting off 1 if it rounded up. */
       avg = _mm_sub_epi8(avg, _mm_and_si128(_mm_xor_si128(a,b),
                                             _mm_set1_epi8(1)));
@@ -237,38 +257,42 @@
     * Here we zero b and d, which become c and a respectively at the start of
     * the loop.
     */
-   png_debug(1, "in png_read_filter_row_paeth3_sse2");
+   png_size_t rb;
    const __m128i zero = _mm_setzero_si128();
    __m128i c, b = zero,
            a, d = zero;
 
-   int rb = row_info->rowbytes;
+   png_debug(1, "in png_read_filter_row_paeth3_sse2");
+
+   rb = row_info->rowbytes;
    while (rb >= 4) {
       /* It's easiest to do this math (particularly, deal with pc) with 16-bit
        * intermediates.
        */
+      __m128i pa,pb,pc,smallest,nearest;
       c = b; b = _mm_unpacklo_epi8(load4(prev), zero);
       a = d; d = _mm_unpacklo_epi8(load4(row ), zero);
 
       /* (p-a) == (a+b-c - a) == (b-c) */
-      __m128i pa = _mm_sub_epi16(b,c);
+   
+      pa = _mm_sub_epi16(b,c);
 
       /* (p-b) == (a+b-c - b) == (a-c) */
-      __m128i pb = _mm_sub_epi16(a,c);
+      pb = _mm_sub_epi16(a,c);
 
       /* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
-      __m128i pc = _mm_add_epi16(pa,pb);
+      pc = _mm_add_epi16(pa,pb);
 
       pa = abs_i16(pa);  /* |p-a| */
       pb = abs_i16(pb);  /* |p-b| */
       pc = abs_i16(pc);  /* |p-c| */
 
-      __m128i smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
+      smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
 
       /* Paeth breaks ties favoring a over b over c. */
-      __m128i nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
-                         if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
-                                                                     c));
+      nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
+                 if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
+                                                             c));
 
       /* Note `_epi8`: we need addition to wrap modulo 255. */
       d = _mm_add_epi8(d, nearest);
@@ -282,26 +306,27 @@
       /* It's easiest to do this math (particularly, deal with pc) with 16-bit
        * intermediates.
        */
+      __m128i pa,pb,pc,smallest,nearest;
       c = b; b = _mm_unpacklo_epi8(load3(prev), zero);
       a = d; d = _mm_unpacklo_epi8(load3(row ), zero);
 
       /* (p-a) == (a+b-c - a) == (b-c) */
-      __m128i pa = _mm_sub_epi16(b,c);
+      pa = _mm_sub_epi16(b,c);
 
       /* (p-b) == (a+b-c - b) == (a-c) */
-      __m128i pb = _mm_sub_epi16(a,c);
+      pb = _mm_sub_epi16(a,c);
 
       /* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
-      __m128i pc = _mm_add_epi16(pa,pb);
+      pc = _mm_add_epi16(pa,pb);
 
       pa = abs_i16(pa);  /* |p-a| */
       pb = abs_i16(pb);  /* |p-b| */
       pc = abs_i16(pc);  /* |p-c| */
 
-      __m128i smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
+      smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
 
       /* Paeth breaks ties favoring a over b over c. */
-      __m128i nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
+      nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
                          if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
                                                                      c));
 
@@ -331,13 +356,16 @@
     * Here we zero b and d, which become c and a respectively at the start of
     * the loop.
     */
-   png_debug(1, "in png_read_filter_row_paeth4_sse2");
+   png_size_t rb;
    const __m128i zero = _mm_setzero_si128();
+   __m128i pa,pb,pc,smallest,nearest;
    __m128i c, b = zero,
            a, d = zero;
 
-   int rb = row_info->rowbytes;
-   while (rb > 0) {
+   png_debug(1, "in png_read_filter_row_paeth4_sse2");
+
+   rb = row_info->rowbytes+4;
+   while (rb > 4) {
       /* It's easiest to do this math (particularly, deal with pc) with 16-bit
        * intermediates.
        */
@@ -345,22 +373,22 @@
       a = d; d = _mm_unpacklo_epi8(load4(row ), zero);
 
       /* (p-a) == (a+b-c - a) == (b-c) */
-      __m128i pa = _mm_sub_epi16(b,c);
+      pa = _mm_sub_epi16(b,c);
 
       /* (p-b) == (a+b-c - b) == (a-c) */
-      __m128i pb = _mm_sub_epi16(a,c);
+      pb = _mm_sub_epi16(a,c);
 
       /* (p-c) == (a+b-c - c) == (a+b-c-c) == (b-c)+(a-c) */
-      __m128i pc = _mm_add_epi16(pa,pb);
+      pc = _mm_add_epi16(pa,pb);
 
       pa = abs_i16(pa);  /* |p-a| */
       pb = abs_i16(pb);  /* |p-b| */
       pc = abs_i16(pc);  /* |p-c| */
 
-      __m128i smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
+      smallest = _mm_min_epi16(pc, _mm_min_epi16(pa, pb));
 
       /* Paeth breaks ties favoring a over b over c. */
-      __m128i nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
+      nearest  = if_then_else(_mm_cmpeq_epi16(smallest, pa), a,
                          if_then_else(_mm_cmpeq_epi16(smallest, pb), b,
                                                                      c));
 
diff --git a/libpng-manual.txt b/libpng-manual.txt
index 6cde89a..b81d2a6 100644
--- a/libpng-manual.txt
+++ b/libpng-manual.txt
@@ -1,6 +1,6 @@
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.30 - June 28, 2017
+ libpng version 1.6.31 - July 27, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -11,7 +11,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.30 - June 28, 2017
+ libpng versions 0.97, January 1998, through 1.6.31 - July 27, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
 
@@ -1330,6 +1330,11 @@
     rowbytes = png_get_rowbytes(png_ptr, info_ptr);
 
     rowbytes       - number of bytes needed to hold a row
+                     This value, the bit_depth, color_type,
+                     and the number of channels can change
+                     if you use transforms such as
+                     png_set_expand(). See
+                     png_read_update_info(), below.
 
     signature = png_get_signature(png_ptr, info_ptr);
 
@@ -1448,6 +1453,11 @@
                      the single transparent color for
                      non-paletted images (PNG_INFO_tRNS)
 
+    png_get_eXIf(png_ptr, info_ptr, &exif);
+                     (PNG_INFO_eXIf)
+
+    exif           - Exif profile (array of png_byte)
+
     png_get_hIST(png_ptr, info_ptr, &hist);
                      (PNG_INFO_hIST)
 
@@ -2493,6 +2503,7 @@
              PNG_INFO_gAMA, PNG_INFO_sBIT,
              PNG_INFO_cHRM, PNG_INFO_PLTE,
              PNG_INFO_tRNS, PNG_INFO_bKGD,
+             PNG_INFO_eXIf,
              PNG_INFO_hIST, PNG_INFO_pHYs,
              PNG_INFO_oFFs, PNG_INFO_tIME,
              PNG_INFO_pCAL, PNG_INFO_sRGB,
@@ -3092,6 +3103,11 @@
                      single transparent color for
                      non-paletted images (PNG_INFO_tRNS)
 
+    png_set_eXIf(png_ptr, info_ptr, exif);
+
+    hist           - Exif profile (array of
+                     png_byte) (PNG_INFO_eXIf)
+
     png_set_hIST(png_ptr, info_ptr, hist);
 
     hist           - histogram of palette (array of
@@ -5200,6 +5216,11 @@
 enforced, and the palette was always limited to 256 entries. An over-length
 PLTE chunk found in an input PNG is silently truncated.
 
+Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
+attempt to decode the Exif profile; it simply returns a byte array
+containing the profile to the calling application which must do its own
+decoding.
+
 XIII.  Detecting libpng
 
 The png_get_io_ptr() function has been present since libpng-0.88, has never
@@ -5383,7 +5404,7 @@
 an official declaration.
 
 This is your unofficial assurance that libpng from version 0.71 and
-upward through 1.6.30 are Y2K compliant.  It is my belief that earlier
+upward through 1.6.31 are Y2K compliant.  It is my belief that earlier
 versions were also Y2K compliant.
 
 Libpng only has two year fields.  One is a 2-byte unsigned integer
diff --git a/libpng.3 b/libpng.3
index 12eb2e2..345aba1 100644
--- a/libpng.3
+++ b/libpng.3
@@ -1,6 +1,6 @@
-.TH LIBPNG 3 "June 28, 2017"
+.TH LIBPNG 3 "July 27, 2017"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.6.30
+libpng \- Portable Network Graphics (PNG) Reference Library 1.6.31
 .SH SYNOPSIS
 \fB
 #include <png.h>\fP
@@ -97,6 +97,8 @@
 
 \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
 
+\fBpng_uint_32 png_get_eXIf (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fI*exif\fP\fB);\fP
+
 \fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
 
 \fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
@@ -347,6 +349,8 @@
 
 \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
 
+\fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP
+
 \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
 
 \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
@@ -510,7 +514,7 @@
 .SH LIBPNG.TXT
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.30 - June 28, 2017
+ libpng version 1.6.31 - July 27, 2017
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
@@ -521,7 +525,7 @@
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.30 - June 28, 2017
+ libpng versions 0.97, January 1998, through 1.6.31 - July 27, 2017
  Updated and distributed by Glenn Randers-Pehrson
  Copyright (c) 1998-2017 Glenn Randers-Pehrson
 
@@ -1840,6 +1844,11 @@
     rowbytes = png_get_rowbytes(png_ptr, info_ptr);
 
     rowbytes       - number of bytes needed to hold a row
+                     This value, the bit_depth, color_type,
+                     and the number of channels can change
+                     if you use transforms such as
+                     png_set_expand(). See
+                     png_read_update_info(), below.
 
     signature = png_get_signature(png_ptr, info_ptr);
 
@@ -1958,6 +1967,11 @@
                      the single transparent color for
                      non-paletted images (PNG_INFO_tRNS)
 
+    png_get_eXIf(png_ptr, info_ptr, &exif);
+                     (PNG_INFO_eXIf)
+
+    exif           - Exif profile (array of png_byte)
+
     png_get_hIST(png_ptr, info_ptr, &hist);
                      (PNG_INFO_hIST)
 
@@ -3003,6 +3017,7 @@
              PNG_INFO_gAMA, PNG_INFO_sBIT,
              PNG_INFO_cHRM, PNG_INFO_PLTE,
              PNG_INFO_tRNS, PNG_INFO_bKGD,
+             PNG_INFO_eXIf,
              PNG_INFO_hIST, PNG_INFO_pHYs,
              PNG_INFO_oFFs, PNG_INFO_tIME,
              PNG_INFO_pCAL, PNG_INFO_sRGB,
@@ -3602,6 +3617,11 @@
                      single transparent color for
                      non-paletted images (PNG_INFO_tRNS)
 
+    png_set_eXIf(png_ptr, info_ptr, exif);
+
+    hist           - Exif profile (array of
+                     png_byte) (PNG_INFO_eXIf)
+
     png_set_hIST(png_ptr, info_ptr, hist);
 
     hist           - histogram of palette (array of
@@ -5710,6 +5730,11 @@
 enforced, and the palette was always limited to 256 entries. An over-length
 PLTE chunk found in an input PNG is silently truncated.
 
+Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
+attempt to decode the Exif profile; it simply returns a byte array
+containing the profile to the calling application which must do its own
+decoding.
+
 .SH XIII.  Detecting libpng
 
 The png_get_io_ptr() function has been present since libpng-0.88, has never
@@ -5893,7 +5918,7 @@
 an official declaration.
 
 This is your unofficial assurance that libpng from version 0.71 and
-upward through 1.6.30 are Y2K compliant.  It is my belief that earlier
+upward through 1.6.31 are Y2K compliant.  It is my belief that earlier
 versions were also Y2K compliant.
 
 Libpng only has two year fields.  One is a 2-byte unsigned integer
@@ -5995,7 +6020,7 @@
  ...
  1.5.28                  15    10528  15.so.15.28[.0]
  ...
- 1.6.30                  16    10630  16.so.16.30[.0]
+ 1.6.31                  16    10631  16.so.16.31[.0]
 
 Henceforth the source version will match the shared-library minor
 and patch numbers; the shared-library major version number will be
@@ -6051,7 +6076,7 @@
 
 Thanks to Frank J. T. Wojcik for helping with the documentation.
 
-Libpng version 1.6.30 - June 28, 2017:
+Libpng version 1.6.31 - July 27, 2017:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
 
@@ -6076,7 +6101,7 @@
 
 This code is released under the libpng license.
 
-libpng versions 1.0.7, July 1, 2000 through 1.6.30, June 28, 2017 are
+libpng versions 1.0.7, July 1, 2000 through 1.6.31, July 27, 2017 are
 Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
 derived from libpng-1.0.6, and are distributed according to the same
 disclaimer and license as libpng-1.0.6 with the following individuals
@@ -6204,7 +6229,7 @@
 
 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-June 28, 2017
+July 27, 2017
 
 .\" end of man page
 
diff --git a/libpng.pc.in b/libpng.pc.in
index 3e7e2c5..9708e9a 100644
--- a/libpng.pc.in
+++ b/libpng.pc.in
@@ -6,6 +6,7 @@
 Name: libpng
 Description: Loads and saves PNG files
 Version: @PNGLIB_VERSION@
+Requires: zlib
 Libs: -L${libdir} -lpng@PNGLIB_MAJOR@@PNGLIB_MINOR@
 Libs.private: @LIBS@
 Cflags: -I${includedir}
diff --git a/libpngpf.3 b/libpngpf.3
index c7ae9ed..70992ab 100644
--- a/libpngpf.3
+++ b/libpngpf.3
@@ -1,6 +1,6 @@
 .TH LIBPNGPF 3 "April 1, 2017"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.6.30
+libpng \- Portable Network Graphics (PNG) Reference Library 1.6.31
 (private functions)
 .SH SYNOPSIS
 \fB\fB#include \fI\fI"pngpriv.h"
diff --git a/png.c b/png.c
index 40688be..ae5e1d9 100644
--- a/png.c
+++ b/png.c
@@ -1,7 +1,7 @@
 
 /* png.c - location for general purpose libpng functions
  *
- * Last changed in libpng 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  * Copyright (c) 1998-2002,2004,2006-2017 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.)
@@ -14,7 +14,27 @@
 #include "pngpriv.h"
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_6_30 Your_png_h_is_not_version_1_6_30;
+typedef png_libpng_version_1_6_31 Your_png_h_is_not_version_1_6_31;
+
+#ifdef __GNUC__
+/* The version tests may need to be added to, but the problem warning has
+ * consistently been fixed in GCC versions which obtain wide-spread release.
+ * The problem is that many versions of GCC rearrange comparison expressions in
+ * the optimizer in such a way that the results of the comparison will change
+ * if signed integer overflow occurs.  Such comparisons are not permitted in
+ * ANSI C90, however GCC isn't clever enough to work out that that do not occur
+ * below in png_ascii_from_fp and png_muldiv, so it produces a warning with
+ * -Wextra.  Unfortunately this is highly dependent on the optimizer and the
+ * machine architecture so the warning comes and goes unpredictably and is
+ * impossible to "fix", even were that a good idea.
+ */
+#if __GNUC__ == 7 && __GNUC_MINOR__ == 1
+#define GCC_STRICT_OVERFLOW 1
+#endif /* GNU 7.1.x */
+#endif /* GNU */
+#ifndef GCC_STRICT_OVERFLOW
+#define GCC_STRICT_OVERFLOW 0
+#endif
 
 /* Tells libpng that we have already handled the first "num_bytes" bytes
  * of the PNG file signature.  If the PNG data is embedded into another
@@ -595,6 +615,16 @@
    }
 #endif
 
+#ifdef PNG_eXIf_SUPPORTED
+   /* Free any eXIf entry */
+   if (((mask & PNG_FREE_EXIF) & info_ptr->free_me) != 0)
+   {
+      png_free(png_ptr, info_ptr->exif);
+      info_ptr->exif = NULL;
+      info_ptr->valid &= ~PNG_INFO_eXIf;
+   }
+#endif
+
 #ifdef PNG_hIST_SUPPORTED
    /* Free any hIST entry */
    if (((mask & PNG_FREE_HIST) & info_ptr->free_me) != 0)
@@ -776,14 +806,14 @@
 #else
 #  ifdef __STDC__
    return PNG_STRING_NEWLINE \
-      "libpng version 1.6.30 - June 28, 2017" PNG_STRING_NEWLINE \
+      "libpng version 1.6.31 - July 27, 2017" PNG_STRING_NEWLINE \
       "Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson" \
       PNG_STRING_NEWLINE \
       "Copyright (c) 1996-1997 Andreas Dilger" PNG_STRING_NEWLINE \
       "Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc." \
       PNG_STRING_NEWLINE;
 #  else
-   return "libpng version 1.6.30 - June 28, 2017\
+   return "libpng version 1.6.31 - July 27, 2017\
       Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson\
       Copyright (c) 1996-1997 Andreas Dilger\
       Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
@@ -2857,6 +2887,14 @@
 /* Function to format a floating point value in ASCII with a given
  * precision.
  */
+#if GCC_STRICT_OVERFLOW
+#pragma GCC diagnostic push
+/* The problem arises below with exp_b10, which can never overflow because it
+ * comes, originally, from frexp and is therefore limited to a range which is
+ * typically +/-710 (log2(DBL_MAX)/log2(DBL_MIN)).
+ */
+#pragma GCC diagnostic warning "-Wstrict-overflow=2"
+#endif /* GCC_STRICT_OVERFLOW */
 void /* PRIVATE */
 png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
     double fp, unsigned int precision)
@@ -2946,7 +2984,7 @@
              */
             if (exp_b10 < 0 && exp_b10 > -3) /* PLUS 3 TOTAL 4 */
             {
-               czero = (unsigned int)(-exp_b10); /* PLUS 2 digits: TOTAL 3 */
+               czero = 0U-exp_b10; /* PLUS 2 digits: TOTAL 3 */
                exp_b10 = 0;      /* Dot added below before first output. */
             }
             else
@@ -3087,7 +3125,7 @@
 
             /* Check for an exponent, if we don't need one we are
              * done and just need to terminate the string.  At
-             * this point exp_b10==(-1) is effectively if flag - it got
+             * this point exp_b10==(-1) is effectively a flag - it got
              * to '-1' because of the decrement after outputting
              * the decimal point above (the exponent required is
              * *not* -1!)
@@ -3101,7 +3139,7 @@
                 * zeros were *not* output, so this doesn't increase
                 * the output count.
                 */
-               while (--exp_b10 >= 0) *ascii++ = 48;
+               while (exp_b10-- > 0) *ascii++ = 48;
 
                *ascii = 0;
 
@@ -3131,11 +3169,11 @@
                if (exp_b10 < 0)
                {
                   *ascii++ = 45; --size; /* '-': PLUS 1 TOTAL 3+precision */
-                  uexp_b10 = (unsigned int)(-exp_b10);
+                  uexp_b10 = 0U-exp_b10;
                }
 
                else
-                  uexp_b10 = (unsigned int)exp_b10;
+                  uexp_b10 = 0U+exp_b10;
 
                cdigits = 0;
 
@@ -3178,6 +3216,9 @@
    /* Here on buffer too small. */
    png_error(png_ptr, "ASCII conversion buffer too small");
 }
+#if GCC_STRICT_OVERFLOW
+#pragma GCC diagnostic pop
+#endif /* GCC_STRICT_OVERFLOW */
 
 #  endif /* FLOATING_POINT */
 
@@ -3291,6 +3332,15 @@
  * the nearest .00001).  Overflow and divide by zero are signalled in
  * the result, a boolean - true on success, false on overflow.
  */
+#if GCC_STRICT_OVERFLOW /* from above */
+/* It is not obvious which comparison below gets optimized in such a way that
+ * signed overflow would change the result; looking through the code does not
+ * reveal any tests which have the form GCC complains about, so presumably the
+ * optimizer is moving an add or subtract into the 'if' somewhere.
+ */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic warning "-Wstrict-overflow=2"
+#endif /* GCC_STRICT_OVERFLOW */
 int
 png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times,
     png_int_32 divisor)
@@ -3405,6 +3455,9 @@
 
    return 0;
 }
+#if GCC_STRICT_OVERFLOW
+#pragma GCC diagnostic pop
+#endif /* GCC_STRICT_OVERFLOW */
 #endif /* READ_GAMMA || INCH_CONVERSIONS */
 
 #if defined(PNG_READ_GAMMA_SUPPORTED) || defined(PNG_INCH_CONVERSIONS_SUPPORTED)
diff --git a/png.h b/png.h
index c2c4fdf..4321416 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.6.30, June 28, 2017
+ * libpng version 1.6.31, July 27, 2017
  *
  * Copyright (c) 1998-2002,2004,2006-2017 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -12,7 +12,7 @@
  * Authors and maintainers:
  *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *   libpng versions 0.89, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.6.30, June 28, 2017:
+ *   libpng versions 0.97, January 1998, through 1.6.31, July 27, 2017:
  *     Glenn Randers-Pehrson.
  *   See also "Contributing Authors", below.
  */
@@ -25,7 +25,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.0.7, July 1, 2000 through 1.6.30, June 28, 2017 are
+ * libpng versions 1.0.7, July 1, 2000 through 1.6.31, July 27, 2017 are
  * Copyright (c) 2000-2002, 2004, 2006-2017 Glenn Randers-Pehrson, are
  * derived from libpng-1.0.6, and are distributed according to the same
  * disclaimer and license as libpng-1.0.6 with the following individuals
@@ -213,7 +213,7 @@
  *    ...
  *    1.5.28                  15    10527  15.so.15.28[.0]
  *    ...
- *    1.6.30                  16    10630  16.so.16.30[.0]
+ *    1.6.31                  16    10631  16.so.16.31[.0]
  *
  *    Henceforth the source version will match the shared-library major
  *    and minor numbers; the shared-library major version number will be
@@ -241,13 +241,13 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    June 28, 2017
+ *    July 27, 2017
  *
  *    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 1.6.30 are Y2K compliant.  It is my belief that
+ *    upward through 1.6.31 are Y2K compliant.  It is my belief that
  *    earlier versions were also Y2K compliant.
  *
  *    Libpng only has two year fields.  One is a 2-byte unsigned integer
@@ -309,8 +309,8 @@
  */
 
 /* Version information for png.h - this should match the version in png.c */
-#define PNG_LIBPNG_VER_STRING "1.6.30"
-#define PNG_HEADER_VERSION_STRING " libpng version 1.6.30 - June 28, 2017\n"
+#define PNG_LIBPNG_VER_STRING "1.6.31"
+#define PNG_HEADER_VERSION_STRING " libpng version 1.6.31 - July 27, 2017\n"
 
 #define PNG_LIBPNG_VER_SONUM   16
 #define PNG_LIBPNG_VER_DLLNUM  16
@@ -318,7 +318,7 @@
 /* These should match the first 3 components of PNG_LIBPNG_VER_STRING: */
 #define PNG_LIBPNG_VER_MAJOR   1
 #define PNG_LIBPNG_VER_MINOR   6
-#define PNG_LIBPNG_VER_RELEASE 30
+#define PNG_LIBPNG_VER_RELEASE 31
 
 /* This should match the numeric part of the final component of
  * PNG_LIBPNG_VER_STRING, omitting any leading zero:
@@ -349,7 +349,7 @@
  * version 1.0.0 was mis-numbered 100 instead of 10000).  From
  * version 1.0.1 it's    xxyyzz, where x=major, y=minor, z=release
  */
-#define PNG_LIBPNG_VER 10630 /* 1.6.30 */
+#define PNG_LIBPNG_VER 10631 /* 1.6.31 */
 
 /* Library configuration: these options cannot be changed after
  * the library has been built.
@@ -459,7 +459,7 @@
 /* This triggers a compiler error in png.c, if png.c and png.h
  * do not agree upon the version number.
  */
-typedef char* png_libpng_version_1_6_30;
+typedef char* png_libpng_version_1_6_31;
 
 /* Basic control structions.  Read libpng-manual.txt or libpng.3 for more info.
  *
@@ -776,6 +776,7 @@
 #define PNG_INFO_sPLT 0x2000U  /* ESR, 1.0.6 */
 #define PNG_INFO_sCAL 0x4000U  /* ESR, 1.0.6 */
 #define PNG_INFO_IDAT 0x8000U  /* ESR, 1.0.6 */
+#define PNG_INFO_eXIf 0x10000U /* GR-P, 1.6.31 */
 
 /* This is used for the transformation routines, as some of them
  * change these values for the row.  It also should enable using
@@ -1788,7 +1789,8 @@
 #define PNG_FREE_PLTE 0x1000U
 #define PNG_FREE_TRNS 0x2000U
 #define PNG_FREE_TEXT 0x4000U
-#define PNG_FREE_ALL  0x7fffU
+#define PNG_FREE_EXIF 0x8000U /* Added at libpng-1.6.31 */
+#define PNG_FREE_ALL  0xffffU
 #define PNG_FREE_MUL  0x4220U /* PNG_FREE_SPLT|PNG_FREE_TEXT|PNG_FREE_UNKN */
 
 #ifdef PNG_USER_MEM_SUPPORTED
@@ -2007,6 +2009,13 @@
     png_fixed_point int_blue_Z))
 #endif
 
+#ifdef PNG_eXIf_SUPPORTED
+PNG_EXPORT(246, png_uint_32, png_get_eXIf, (png_const_structrp png_ptr,
+    png_inforp info_ptr, png_bytep *exif));
+PNG_EXPORT(247, void, png_set_eXIf, (png_const_structrp png_ptr,
+    png_inforp info_ptr, const png_bytep exif));
+#endif
+
 #ifdef PNG_gAMA_SUPPORTED
 PNG_FP_EXPORT(137, png_uint_32, png_get_gAMA, (png_const_structrp png_ptr,
     png_const_inforp info_ptr, double *file_gamma))
@@ -2025,9 +2034,6 @@
 #ifdef PNG_hIST_SUPPORTED
 PNG_EXPORT(141, png_uint_32, png_get_hIST, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_uint_16p *hist));
-#endif
-
-#ifdef PNG_hIST_SUPPORTED
 PNG_EXPORT(142, void, png_set_hIST, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_const_uint_16p hist));
 #endif
@@ -3253,7 +3259,7 @@
  * one to use is one more than this.)
  */
 #ifdef PNG_EXPORT_LAST_ORDINAL
-  PNG_EXPORT_LAST_ORDINAL(245);
+  PNG_EXPORT_LAST_ORDINAL(247);
 #endif
 
 #ifdef __cplusplus
diff --git a/pngconf.h b/pngconf.h
index f64592a..af6e80c 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.6.30, June 28, 2017
+ * libpng version 1.6.31, July 27, 2017
  *
  * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
diff --git a/pngerror.c b/pngerror.c
index 00d76f7..ad48bfb 100644
--- a/pngerror.c
+++ b/pngerror.c
@@ -1,8 +1,8 @@
 
 /* pngerror.c - stub functions for i/o and memory allocation
  *
- * Last changed in libpng 1.6.26 [October 20, 2016]
- * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 1998-2002,2004,2006-2017 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.)
  *
@@ -163,7 +163,7 @@
          case PNG_NUMBER_FORMAT_02u:
             /* Expects at least 2 digits. */
             mincount = 2;
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
 
          case PNG_NUMBER_FORMAT_u:
             *--end = digits[number % 10];
@@ -173,7 +173,7 @@
          case PNG_NUMBER_FORMAT_02x:
             /* This format expects at least two digits */
             mincount = 2;
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
 
          case PNG_NUMBER_FORMAT_x:
             *--end = digits[number & 0xf];
diff --git a/pngget.c b/pngget.c
index 141c393..ace9e63 100644
--- a/pngget.c
+++ b/pngget.c
@@ -773,6 +773,24 @@
 }
 #endif
 
+#ifdef PNG_eXIf_SUPPORTED
+png_uint_32 PNGAPI
+png_get_eXIf(png_const_structrp png_ptr, png_inforp info_ptr,
+    png_bytep *exif)
+{
+   png_debug1(1, "in %s retrieval function", "eXIf");
+
+   if (png_ptr != NULL && info_ptr != NULL &&
+       (info_ptr->valid & PNG_INFO_eXIf) != 0 && exif != NULL)
+   {
+      *exif = info_ptr->exif;
+      return (PNG_INFO_eXIf);
+   }
+
+   return (0);
+}
+#endif
+
 #ifdef PNG_hIST_SUPPORTED
 png_uint_32 PNGAPI
 png_get_hIST(png_const_structrp png_ptr, png_inforp info_ptr,
diff --git a/pnginfo.h b/pnginfo.h
index 361ed8b..6e6d46a 100644
--- a/pnginfo.h
+++ b/pnginfo.h
@@ -185,6 +185,11 @@
    png_byte phys_unit_type; /* resolution type (see PNG_RESOLUTION_ below) */
 #endif
 
+#ifdef PNG_eXIf_SUPPORTED
+   int num_exif;
+   png_bytep exif;
+#endif
+
 #ifdef PNG_hIST_SUPPORTED
    /* The hIST chunk contains the relative frequency or importance of the
     * various palette entries, so that a viewer can intelligently select a
diff --git a/pngpriv.h b/pngpriv.h
index a062a8d..ef45ab7 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1,7 +1,7 @@
 
 /* pngpriv.h - private declarations for use inside libpng
  *
- * Last changed in libpng 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  * Copyright (c) 1998-2002,2004,2006-2017 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.)
@@ -35,7 +35,9 @@
  * Windows/Visual Studio) there is no effect; the OS specific tests below are
  * still required (as of 2011-05-02.)
  */
-#define _POSIX_SOURCE 1 /* Just the POSIX 1003.1 and C89 APIs */
+#ifndef _POSIX_SOURCE
+# define _POSIX_SOURCE 1 /* Just the POSIX 1003.1 and C89 APIs */
+#endif
 
 #ifndef PNG_VERSION_INFO_ONLY
 /* Standard library headers not required by png.h: */
@@ -452,6 +454,21 @@
 #  define png_fixed_error(s1,s2) png_err(s1)
 #endif
 
+/* Some fixed point APIs are still required even if not exported because
+ * they get used by the corresponding floating point APIs.  This magic
+ * deals with this:
+ */
+#ifdef PNG_FIXED_POINT_SUPPORTED
+#  define PNGFAPI PNGAPI
+#else
+#  define PNGFAPI /* PRIVATE */
+#endif
+
+#ifndef PNG_VERSION_INFO_ONLY
+/* Other defines specific to compilers can go here.  Try to keep
+ * them inside an appropriate ifdef/endif pair for portability.
+ */
+
 /* C allows up-casts from (void*) to any pointer and (const void*) to any
  * pointer to a const object.  C++ regards this as a type error and requires an
  * explicit, static, cast and provides the static_cast<> rune to ensure that
@@ -480,20 +497,6 @@
 #  define png_aligncastconst(type, value) ((const void*)(value))
 #endif /* __cplusplus */
 
-/* Some fixed point APIs are still required even if not exported because
- * they get used by the corresponding floating point APIs.  This magic
- * deals with this:
- */
-#ifdef PNG_FIXED_POINT_SUPPORTED
-#  define PNGFAPI PNGAPI
-#else
-#  define PNGFAPI /* PRIVATE */
-#endif
-
-#ifndef PNG_VERSION_INFO_ONLY
-/* Other defines specific to compilers can go here.  Try to keep
- * them inside an appropriate ifdef/endif pair for portability.
- */
 #if defined(PNG_FLOATING_POINT_SUPPORTED) ||\
     defined(PNG_FLOATING_ARITHMETIC_SUPPORTED)
    /* png.c requires the following ANSI-C constants if the conversion of
@@ -839,6 +842,7 @@
 #define png_PLTE PNG_U32( 80,  76,  84,  69)
 #define png_bKGD PNG_U32( 98,  75,  71,  68)
 #define png_cHRM PNG_U32( 99,  72,  82,  77)
+#define png_eXIf PNG_U32(101,  88,  73, 102) /* registered July 2017 */
 #define png_fRAc PNG_U32(102,  82,  65,  99) /* registered, not defined */
 #define png_gAMA PNG_U32(103,  65,  77,  65)
 #define png_gIFg PNG_U32(103,  73,  70, 103)
@@ -1438,6 +1442,11 @@
     png_inforp info_ptr, png_uint_32 length),PNG_EMPTY);
 #endif
 
+#ifdef PNG_READ_eXIf_SUPPORTED
+PNG_INTERNAL_FUNCTION(void,png_handle_eXIf,(png_structrp png_ptr,
+    png_inforp info_ptr, png_uint_32 length),PNG_EMPTY);
+#endif
+
 #ifdef PNG_READ_gAMA_SUPPORTED
 PNG_INTERNAL_FUNCTION(void,png_handle_gAMA,(png_structrp png_ptr,
     png_inforp info_ptr, png_uint_32 length),PNG_EMPTY);
diff --git a/pngread.c b/pngread.c
index 106a805..331ce12 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1,8 +1,8 @@
 
 /* pngread.c - read a PNG file
  *
- * Last changed in libpng 1.6.26 [October 20, 2016]
- * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 1998-2002,2004,2006-2017 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.)
  *
@@ -1883,7 +1883,7 @@
          {
             case 4:
                entry[afirst ? 0 : 3] = (png_uint_16)alpha;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case 3:
                if (alpha < 65535)
@@ -1905,7 +1905,7 @@
 
             case 2:
                entry[1 ^ afirst] = (png_uint_16)alpha;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case 1:
                if (alpha < 65535)
@@ -1934,6 +1934,7 @@
          {
             case 4:
                entry[afirst ? 0 : 3] = (png_byte)alpha;
+               /* FALLTHROUGH */
             case 3:
                entry[afirst + (2 ^ bgr)] = (png_byte)blue;
                entry[afirst + 1] = (png_byte)green;
@@ -1942,6 +1943,7 @@
 
             case 2:
                entry[1 ^ afirst] = (png_byte)alpha;
+               /* FALLTHROUGH */
             case 1:
                entry[afirst] = (png_byte)green;
                break;
@@ -2861,7 +2863,7 @@
       case P_sRGB:
          /* Change to 8-bit sRGB */
          png_set_alpha_mode_fixed(png_ptr, PNG_ALPHA_PNG, PNG_GAMMA_sRGB);
-         /* FALL THROUGH */
+         /* FALLTHROUGH */
 
       case P_FILE:
          if (png_ptr->bit_depth > 8)
@@ -3179,8 +3181,7 @@
             image->colormap_entries == 244 /* 216 + 1 + 27 */)
             break;
 
-         /* goto bad_output; */
-         /* FALL THROUGH */
+         goto bad_output;
 
       default:
       bad_output:
diff --git a/pngrtran.c b/pngrtran.c
index 3886833..9a30ddf 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 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  * Copyright (c) 1998-2002,2004,2006-2017 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.)
@@ -49,6 +49,7 @@
       case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
          png_warning(png_ptr,
              "Can't discard critical data on CRC error");
+         /* FALLTHROUGH */
       case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
 
       case PNG_CRC_DEFAULT:
@@ -1253,7 +1254,7 @@
             default:
 
             case 8:
-               /* FALL THROUGH (Already 8 bits) */
+               /* FALLTHROUGH */ /*  (Already 8 bits) */
 
             case 16:
                /* Already a full 16 bits */
diff --git a/pngrutil.c b/pngrutil.c
index f60545b..7fe5cd1 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1,7 +1,7 @@
 
 /* pngrutil.c - utilities to read a PNG file
  *
- * Last changed in libpng 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.31 [July 27, 2017]
  * Copyright (c) 1998-2002,2004,2006-2017 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.)
@@ -2009,6 +2009,44 @@
 }
 #endif
 
+#ifdef PNG_READ_eXIf_SUPPORTED
+void /* PRIVATE */
+png_handle_eXIf(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
+{
+   unsigned int i;
+   png_bytep eXIf_buf;
+
+   png_debug(1, "in png_handle_eXIf");
+
+   if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
+      png_chunk_error(png_ptr, "missing IHDR");
+
+   else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_eXIf) != 0)
+   {
+      png_crc_finish(png_ptr, length);
+      png_chunk_benign_error(png_ptr, "duplicate");
+      return;
+   }
+
+   eXIf_buf = png_voidcast(png_bytep,
+             png_malloc_warn(png_ptr, length));
+
+   for (i = 0; i < length; i++)
+   {
+      png_byte buf[1];
+      png_crc_read(png_ptr, buf, 1);
+      eXIf_buf[i] = buf[0];
+   }
+
+   if (png_crc_finish(png_ptr, 0) != 0)
+      return;
+
+   info_ptr->num_exif = length;
+
+   png_set_eXIf(png_ptr, info_ptr, eXIf_buf);
+}
+#endif
+
 #ifdef PNG_READ_hIST_SUPPORTED
 void /* PRIVATE */
 png_handle_hIST(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
@@ -2978,7 +3016,7 @@
          case 2:
             png_ptr->user_chunk_cache_max = 1;
             png_chunk_benign_error(png_ptr, "no space in chunk cache");
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
          case 1:
             /* NOTE: prior to 1.6.0 this case resulted in an unknown critical
              * chunk being skipped, now there will be a hard error below.
@@ -2987,7 +3025,7 @@
 
          default: /* not at limit */
             --(png_ptr->user_chunk_cache_max);
-            /* FALL THROUGH */
+            /* FALLTHROUGH */
          case 0: /* no limit */
 #  endif /* USER_LIMITS */
             /* Here when the limit isn't reached or when limits are compiled
diff --git a/pngset.c b/pngset.c
index fb495ac..9984735 100644
--- a/pngset.c
+++ b/pngset.c
@@ -1,7 +1,7 @@
 
 /* pngset.c - storage of image information into info struct
  *
- * Last changed in libpng 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.30 [June 28, 2017]
  * Copyright (c) 1998-2017 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.)
@@ -134,6 +134,39 @@
 
 #endif /* cHRM */
 
+#ifdef PNG_eXIf_SUPPORTED
+void PNGAPI
+png_set_eXIf(png_const_structrp png_ptr, png_inforp info_ptr,
+    const png_bytep eXIf_buf)
+{
+   int i;
+
+   png_debug1(1, "in %s storage function", "eXIf");
+
+   if (png_ptr == NULL || info_ptr == NULL)
+      return;
+
+   png_free_data(png_ptr, info_ptr, PNG_FREE_EXIF, 0);
+
+   info_ptr->exif = png_voidcast(png_bytep, png_malloc_warn(png_ptr,
+       info_ptr->num_exif));
+
+   if (info_ptr->exif == NULL)
+   {
+      png_warning(png_ptr, "Insufficient memory for eXIf chunk data");
+
+      return;
+   }
+
+   info_ptr->free_me |= PNG_FREE_EXIF;
+
+   for (i = 0; i < info_ptr->num_exif; i++)
+      info_ptr->exif[i] = eXIf_buf[i];
+
+   info_ptr->valid |= PNG_INFO_eXIf;
+}
+#endif /* eXIf */
+
 #ifdef PNG_gAMA_SUPPORTED
 void PNGFAPI
 png_set_gAMA_fixed(png_const_structrp png_ptr, png_inforp info_ptr,
diff --git a/pngstruct.h b/pngstruct.h
index 749d7e3..44b79de 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -479,5 +479,8 @@
    png_colorspace   colorspace;
 #endif
 #endif
+
+/* New member added in libpng-1.6.31 */
+   int num_exif;
 };
 #endif /* PNGSTRUCT_H */
diff --git a/pngtest.c b/pngtest.c
index d2938d1..bdd37db 100644
--- a/pngtest.c
+++ b/pngtest.c
@@ -1192,6 +1192,14 @@
       }
    }
 #endif
+#ifdef PNG_eXIf_SUPPORTED
+   {
+      png_bytep exif;
+
+      if (png_get_eXIf(read_ptr, read_info_ptr, &exif) != 0)
+         png_set_eXIf(write_ptr, write_info_ptr, exif);
+   }
+#endif
 #ifdef PNG_hIST_SUPPORTED
    {
       png_uint_16p hist;
@@ -1530,6 +1538,14 @@
       }
    }
 #endif
+#ifdef PNG_eXIf_SUPPORTED
+   {
+      png_bytep exif;
+
+      if (png_get_eXIf(read_ptr, end_info_ptr, &exif) != 0)
+         png_set_eXIf(write_ptr, write_end_info_ptr, exif);
+   }
+#endif
 #ifdef PNG_tIME_SUPPORTED
    {
       png_timep mod_time;
@@ -2088,4 +2104,4 @@
 #endif
 
 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_6_30 Your_png_h_is_not_version_1_6_30;
+typedef png_libpng_version_1_6_31 Your_png_h_is_not_version_1_6_31;
diff --git a/pngtest.png b/pngtest.png
index cb3fef4..66df0c4 100644
--- a/pngtest.png
+++ b/pngtest.png
Binary files differ
diff --git a/pngtrans.c b/pngtrans.c
index 6c8c646..326ac33 100644
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -1,7 +1,7 @@
 
 /* pngtrans.c - transforms the data in a row (used by both readers and writers)
  *
- * Last changed in libpng 1.6.30 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.30 [June 28, 2017]
  * Copyright (c) 1998-2002,2004,2006-2017 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.)
diff --git a/pngwrite.c b/pngwrite.c
index 07088ee..70d47c4 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -1,8 +1,8 @@
 
 /* pngwrite.c - general routines to write a PNG file
  *
- * Last changed in libpng 1.6.26 [October 20, 2016]
- * Copyright (c) 1998-2002,2004,2006-2016 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.31 [July 27, 2017]
+ * Copyright (c) 1998-2002,2004,2006-2017 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.)
  *
@@ -1007,8 +1007,8 @@
          case 5:
          case 6:
          case 7: png_app_error(png_ptr, "Unknown row filter for method 0");
-            /* FALL THROUGH */
 #endif /* WRITE_FILTER */
+            /* FALLTHROUGH */
          case PNG_FILTER_VALUE_NONE:
             png_ptr->do_filter = PNG_FILTER_NONE; break;
 
@@ -1875,7 +1875,7 @@
                tRNS[i] = entry[afirst ? 0 : 3];
                if (tRNS[i] < 255)
                   num_trans = i+1;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
             case 3:
                palette[i].blue = entry[afirst + (2 ^ bgr)];
                palette[i].green = entry[afirst + 1];
@@ -1886,7 +1886,7 @@
                tRNS[i] = entry[1 ^ afirst];
                if (tRNS[i] < 255)
                   num_trans = i+1;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
             case 1:
                palette[i].blue = palette[i].red = palette[i].green =
                   entry[afirst];
diff --git a/pngwutil.c b/pngwutil.c
index dd80058..348bb52 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -1473,6 +1473,37 @@
 }
 #endif
 
+#ifdef PNG_WRITE_eXIf_SUPPORTED
+/* Write the Exif data */
+void /* PRIVATE */
+png_write_eXIf(png_structrp png_ptr, png_bytep exif, int num_exif)
+{
+   int i;
+   png_byte buf[3];
+
+   png_debug(1, "in png_write_eXIf");
+
+   if (num_exif > (int)png_ptr->num_exif)
+   {
+      png_debug2(3, "num_exif = %d, png_ptr->num_exif = %d", num_exif,
+          png_ptr->num_exif);
+
+      png_warning(png_ptr, "Invalid number of exif bytes specified");
+      return;
+   }
+
+   png_write_chunk_header(png_ptr, png_eXIf, (png_uint_32)(num_exif));
+
+   for (i = 0; i < num_exif; i++)
+   {
+      buf[i] = exif[i];
+      png_write_chunk_data(png_ptr, buf, (png_size_t)1);
+   }
+
+   png_write_chunk_end(png_ptr);
+}
+#endif
+
 #ifdef PNG_WRITE_hIST_SUPPORTED
 /* Write the histogram */
 void /* PRIVATE */
diff --git a/projects/vstudio/README.txt b/projects/vstudio/README.txt
index 1856022..38c159c 100644
--- a/projects/vstudio/README.txt
+++ b/projects/vstudio/README.txt
@@ -1,7 +1,7 @@
 
 VisualStudio instructions
 
-libpng version 1.6.30 - June 28, 2017
+libpng version 1.6.31 - July 27, 2017
 
 Copyright (c) 2010,2013,2015 Glenn Randers-Pehrson
 
diff --git a/projects/vstudio/zlib.props b/projects/vstudio/zlib.props
index df9c4d6..f3fa101 100644
--- a/projects/vstudio/zlib.props
+++ b/projects/vstudio/zlib.props
@@ -2,7 +2,7 @@
 <!--
  * zlib.props - location of zlib source
  *
- * libpng version 1.6.30 - June 28, 2017
+ * libpng version 1.6.31 - July 27, 2017
  *
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  *
diff --git a/scripts/README.txt b/scripts/README.txt
index 24b1228..76e70e6 100644
--- a/scripts/README.txt
+++ b/scripts/README.txt
@@ -1,9 +1,11 @@
 
-Makefiles for  libpng version 1.6.30 - June 28, 2017
+Makefiles for  libpng version 1.6.31 - July 27, 2017
 
 pnglibconf.h.prebuilt       =>  Stores configuration settings
  makefile.linux    =>  Linux/ELF makefile
-                       (gcc, creates libpng16.so.16.1.6.30)
+                       (gcc, creates libpng16.so.16.1.6.31)
+ makefile.linux-opt=>  Linux/ELF makefile with hardware optimizations on
+                       (gcc, creates libpng16.so.16.1.6.31)
  makefile.gcc      =>  Generic makefile (gcc, creates static libpng.a)
  makefile.knr      =>  Archaic UNIX Makefile that converts files with
                        ansi2knr (Requires ansi2knr.c from
@@ -33,12 +35,12 @@
  makefile.os2      =>  OS/2 Makefile (gcc and emx, requires libpng.def)
  makefile.sco      =>  For SCO OSr5  ELF and Unixware 7 with Native cc
  makefile.sggcc    =>  Silicon Graphics (gcc,
-                       creates libpng16.so.16.1.6.30)
+                       creates libpng16.so.16.1.6.31)
  makefile.sgi      =>  Silicon Graphics IRIX makefile (cc, creates static lib)
  makefile.solaris  =>  Solaris 2.X makefile (gcc,
-                       creates libpng16.so.16.1.6.30)
+                       creates libpng16.so.16.1.6.31)
  makefile.so9      =>  Solaris 9 makefile (gcc,
-                       creates libpng16.so.16.1.6.30)
+                       creates libpng16.so.16.1.6.31)
  makefile.std      =>  Generic UNIX makefile (cc, creates static libpng.a)
  makefile.sunos    =>  Sun makefile
  makefile.32sunu   =>  Sun Ultra 32-bit makefile
diff --git a/scripts/def.c b/scripts/def.c
index f474f1f..aedaec8 100644
--- a/scripts/def.c
+++ b/scripts/def.c
@@ -21,7 +21,7 @@
 PNG_DFN "OS2 CODE PRELOAD MOVEABLE DISCARDABLE"
 PNG_DFN ""
 PNG_DFN "EXPORTS"
-PNG_DFN ";Version 1.6.30"
+PNG_DFN ";Version 1.6.31"
 
 #define PNG_EXPORTA(ordinal, type, name, args, attributes)\
         PNG_DFN "@" SYMBOL_PREFIX "@@" name "@"
diff --git a/scripts/libpng-config-head.in b/scripts/libpng-config-head.in
index 4efbab7..9e7d952 100644
--- a/scripts/libpng-config-head.in
+++ b/scripts/libpng-config-head.in
@@ -11,7 +11,7 @@
 
 # Modeled after libxml-config.
 
-version=1.6.30
+version=1.6.31
 prefix=""
 libdir=""
 libs=""
diff --git a/scripts/libpng.pc.in b/scripts/libpng.pc.in
index 08365a4..8210520 100644
--- a/scripts/libpng.pc.in
+++ b/scripts/libpng.pc.in
@@ -5,6 +5,6 @@
 
 Name: libpng
 Description: Loads and saves PNG files
-Version: 1.6.30
+Version: 1.6.31
 Libs: -L${libdir} -lpng16
 Cflags: -I${includedir}
diff --git a/scripts/makefile.cegcc b/scripts/makefile.cegcc
index 6043845..ef17dab 100644
--- a/scripts/makefile.cegcc
+++ b/scripts/makefile.cegcc
@@ -23,7 +23,7 @@
 
 VERMAJ = 1
 VERMIN = 6
-VERMIC = 30
+VERMIC = 31
 VER = $(VERMAJ).$(VERMIN).$(VERMIC)
 NAME = libpng
 PACKAGE = $(NAME)-$(VER)
diff --git a/scripts/makefile.linux b/scripts/makefile.linux
index f3f9550..8bb5ba7 100644
--- a/scripts/makefile.linux
+++ b/scripts/makefile.linux
@@ -10,7 +10,7 @@
 # Library name:
 LIBNAME = libpng16
 PNGMAJ = 16
-RELEASE = 30
+RELEASE = 31
 
 # Shared library names:
 LIBSO=$(LIBNAME).so
diff --git a/scripts/makefile.linux-opt b/scripts/makefile.linux-opt
new file mode 100644
index 0000000..f93c545
--- /dev/null
+++ b/scripts/makefile.linux-opt
@@ -0,0 +1,265 @@
+# makefile for libpng.a and libpng16.so on Linux ELF with gcc
+# Copyright (C) 1998,1999,2002,2006,2008,2010-2014,2017 Greg Roelofs and
+# Glenn Randers-Pehrson
+# Copyright (C) 1996,1997 Andreas Dilger
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Library name:
+LIBNAME = libpng16
+PNGMAJ = 16
+RELEASE = 31
+
+# Shared library names:
+LIBSO=$(LIBNAME).so
+LIBSOMAJ=$(LIBNAME).so.$(PNGMAJ)
+LIBSOREL=$(LIBSOMAJ).$(RELEASE)
+OLDSO=libpng.so
+
+# Utilities:
+AR_RC=ar rc
+CC=gcc
+MKDIR_P=mkdir -p
+LN_SF=ln -sf
+RANLIB=ranlib
+CP=cp
+RM_F=/bin/rm -f
+
+# where "make install" puts libpng16.a, libpng16.so*,
+# libpng16/png.h, libpng16/pngconf.h, and libpng16/pnglibconf.h
+# Prefix must be a full pathname.
+prefix=/usr/local
+exec_prefix=$(prefix)
+
+# Where the zlib library and include files are located.
+#ZLIBLIB=/usr/local/lib
+#ZLIBINC=/usr/local/include
+ZLIBLIB=../zlib
+ZLIBINC=../zlib
+
+ALIGN=
+# for i386:
+#ALIGN=-malign-loops=2 -malign-functions=2
+
+#WARNMORE=-Wwrite-strings -Wpointer-arith \
+#	-Wmissing-declarations -Wtraditional -Wcast-align \
+#	-Wstrict-prototypes -Wmissing-prototypes
+
+# for pgcc version 2.95.1, -O3 is buggy; don't use it.
+
+CPPFLAGS=-I$(ZLIBINC)
+CPPFLAGS += -DPNG_ARM_NEON
+CPPFLAGS += -DPNG_MIPS_MSA
+CPPFLAGS += -DPNG_INTEL_SSE
+CPPFLAGS += -DPNG_POWERPC_VSX
+CPPFLAGS+=-ansi -pedantic -Wextra -Wall -Wshadow -Wno-sign-conversion
+CPPFLAGS+=-W -Wall -Wconversion $(ALIGN)
+# CPPFLAGS+=$(WARNMORE)
+CFLAGS= -O3 -funroll-loops
+
+LDFLAGS=-L. -Wl,-rpath,. -L$(ZLIBLIB) -Wl,-rpath,$(ZLIBLIB) -lpng16 -lz -lm
+LDFLAGS_A=-L$(ZLIBLIB) -Wl,-rpath,$(ZLIBLIB) libpng.a -lz -lm
+
+INCPATH=$(prefix)/include
+LIBPATH=$(exec_prefix)/lib
+MANPATH=$(prefix)/man
+BINPATH=$(exec_prefix)/bin
+
+# override DESTDIR= on the make install command line to easily support
+# installing into a temporary location.  Example:
+#
+#    make install DESTDIR=/tmp/build/libpng
+#
+# If you're going to install into a temporary location
+# via DESTDIR, $(DESTDIR)$(prefix) must already exist before
+# you execute make install.
+DESTDIR=
+
+DB=$(DESTDIR)$(BINPATH)
+DI=$(DESTDIR)$(INCPATH)
+DL=$(DESTDIR)$(LIBPATH)
+DM=$(DESTDIR)$(MANPATH)
+
+# Pre-built configuration
+# See scripts/pnglibconf.mak for more options
+PNGLIBCONF_H_PREBUILT = scripts/pnglibconf.h.prebuilt
+
+OBJS =  png.o pngset.o pngget.o pngrutil.o pngtrans.o pngwutil.o \
+	pngread.o pngrio.o pngwio.o pngwrite.o pngrtran.o \
+	pngwtran.o pngmem.o pngerror.o pngpread.o \
+	arm/arm_init.o arm/filter_neon_intrinsics.o \
+	mips/mips_init.o mips/filter_msa_intrinsics.o \
+	intel/intel_init.o intel/filter_sse2_intrinsics.o\
+	powerpc/powerpc_init.o powerpc/filter_vsx_intrinsics.o
+
+OBJSDLL = $(OBJS:.o=.pic.o)
+
+.SUFFIXES:      .c .o .pic.o
+
+.c.o:
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -o $@ $<
+
+.c.pic.o:
+	$(CC) -c $(CPPFLAGS) $(CFLAGS) -fPIC -o $@ $*.c
+
+all: libpng.a $(LIBSO) pngtest pngtest-static libpng.pc libpng-config
+
+pnglibconf.h: $(PNGLIBCONF_H_PREBUILT)
+	$(CP) $(PNGLIBCONF_H_PREBUILT) $@
+
+libpng.a: $(OBJS)
+	$(AR_RC) $@ $(OBJS)
+	$(RANLIB) $@
+
+libpng.pc:
+	cat scripts/libpng.pc.in | sed -e s!@prefix@!$(prefix)! \
+	-e s!@exec_prefix@!$(exec_prefix)! \
+	-e s!@libdir@!$(LIBPATH)! \
+	-e s!@includedir@!$(INCPATH)! \
+	-e s!-lpng16!-lpng16\ -lz\ -lm! > libpng.pc
+
+libpng-config:
+	( cat scripts/libpng-config-head.in; \
+	echo prefix=\"$(prefix)\"; \
+	echo I_opts=\"-I$(INCPATH)/$(LIBNAME)\"; \
+	echo L_opts=\"-L$(LIBPATH)\"; \
+	echo R_opts=\"-Wl,-rpath,$(LIBPATH)\"; \
+	echo libs=\"-lpng16 -lz -lm\"; \
+	cat scripts/libpng-config-body.in ) > libpng-config
+	chmod +x libpng-config
+
+$(LIBSO): $(LIBSOMAJ)
+	$(LN_SF) $(LIBSOMAJ) $(LIBSO)
+
+$(LIBSOMAJ): $(OBJSDLL)
+	$(CC) -shared -Wl,-soname,$(LIBSOMAJ) -o $(LIBSOMAJ) $(OBJSDLL)
+
+pngtest: pngtest.o $(LIBSO)
+	$(CC) -o pngtest $(CFLAGS) pngtest.o $(LDFLAGS)
+
+pngtest-static: pngtest.o libpng.a
+	$(CC) -o pngtest-static $(CFLAGS) pngtest.o $(LDFLAGS_A)
+
+test: pngtest pngtest-static
+	@echo ""
+	@echo "   Running pngtest dynamically linked with $(LIBSO):"
+	@echo ""
+	./pngtest
+	@echo ""
+	@echo "   Running pngtest statically linked with libpng.a:"
+	@echo ""
+	./pngtest-static
+
+install-headers: png.h pngconf.h pnglibconf.h
+	-@if [ ! -d $(DI) ]; then $(MKDIR_P) $(DI); fi
+	-@if [ ! -d $(DI)/$(LIBNAME) ]; then $(MKDIR_P) $(DI)/$(LIBNAME); fi
+	cp png.h pngconf.h pnglibconf.h $(DI)/$(LIBNAME)
+	chmod 644 $(DI)/$(LIBNAME)/png.h $(DI)/$(LIBNAME)/pngconf.h $(DI)/$(LIBNAME)/pnglibconf.h
+	-@$(RM_F) $(DI)/png.h $(DI)/pngconf.h $(DI)/pnglibconf.h
+	-@$(RM_F) $(DI)/libpng
+	(cd $(DI); $(LN_SF) $(LIBNAME) libpng; $(LN_SF) $(LIBNAME)/* .)
+
+install-static: install-headers libpng.a
+	-@if [ ! -d $(DL) ]; then $(MKDIR_P) $(DL); fi
+	cp libpng.a $(DL)/$(LIBNAME).a
+	chmod 644 $(DL)/$(LIBNAME).a
+	-@$(RM_F) $(DL)/libpng.a
+	(cd $(DL); $(LN_SF) $(LIBNAME).a libpng.a)
+
+install-shared: install-headers $(LIBSOMAJ) libpng.pc
+	-@if [ ! -d $(DL) ]; then $(MKDIR_P) $(DL); fi
+	-@$(RM_F) $(DL)/$(LIBSO)
+	-@$(RM_F) $(DL)/$(LIBSOREL)
+	-@$(RM_F) $(DL)/$(OLDSO)
+	cp $(LIBSOMAJ) $(DL)/$(LIBSOREL)
+	chmod 755 $(DL)/$(LIBSOREL)
+	(cd $(DL); \
+	$(LN_SF) $(LIBSOREL) $(LIBSO); \
+	$(LN_SF) $(LIBSO) $(OLDSO))
+
+	-@if [ ! -d $(DL)/pkgconfig ]; then $(MKDIR_P) $(DL)/pkgconfig; fi
+	-@$(RM_F) $(DL)/pkgconfig/$(LIBNAME).pc
+	-@$(RM_F) $(DL)/pkgconfig/libpng.pc
+	cp libpng.pc $(DL)/pkgconfig/$(LIBNAME).pc
+	chmod 644 $(DL)/pkgconfig/$(LIBNAME).pc
+	(cd $(DL)/pkgconfig; $(LN_SF) $(LIBNAME).pc libpng.pc)
+
+install-man: libpng.3 libpngpf.3 png.5
+	-@if [ ! -d $(DM) ]; then $(MKDIR_P) $(DM); fi
+	-@if [ ! -d $(DM)/man3 ]; then $(MKDIR_P) $(DM)/man3; fi
+	-@$(RM_F) $(DM)/man3/libpng.3
+	-@$(RM_F) $(DM)/man3/libpngpf.3
+	cp libpng.3 $(DM)/man3
+	cp libpngpf.3 $(DM)/man3
+	-@if [ ! -d $(DM)/man5 ]; then $(MKDIR_P) $(DM)/man5; fi
+	-@$(RM_F) $(DM)/man5/png.5
+	cp png.5 $(DM)/man5
+
+install-config: libpng-config
+	-@if [ ! -d $(DB) ]; then $(MKDIR_P) $(DB); fi
+	-@$(RM_F) $(DB)/libpng-config
+	-@$(RM_F) $(DB)/$(LIBNAME)-config
+	cp libpng-config $(DB)/$(LIBNAME)-config
+	chmod 755 $(DB)/$(LIBNAME)-config
+	(cd $(DB); $(LN_SF) $(LIBNAME)-config libpng-config)
+
+install: install-static install-shared install-man install-config
+
+# If you installed in $(DESTDIR), test-installed won't work until you
+# move the library to its final location.  Use test-dd to test it
+# before then.
+
+test-dd:
+	echo
+	echo Testing installed dynamic shared library in $(DL).
+	$(CC) -I$(DI) $(CPPFLAGS) \
+	   `$(BINPATH)/$(LIBNAME)-config --cflags` pngtest.c \
+	   -L$(DL) -L$(ZLIBLIB) -Wl, -rpath,$(DL) -Wl,-rpath,$(ZLIBLIB) \
+	   -o pngtestd `$(BINPATH)/$(LIBNAME)-config --ldflags`
+	./pngtestd pngtest.png
+
+test-installed:
+	$(CC) $(CPPFLAGS) \
+	   `$(BINPATH)/$(LIBNAME)-config --cflags` pngtest.c \
+	   -L$(ZLIBLIB) -Wl,-rpath,$(ZLIBLIB) \
+	   -o pngtesti `$(BINPATH)/$(LIBNAME)-config --ldflags`
+	./pngtesti pngtest.png
+
+clean:
+	$(RM_F) *.o libpng.a pngtest pngout.png libpng-config \
+	$(LIBSO) $(LIBSOMAJ)* pngtest-static pngtesti \
+	libpng.pc pnglibconf.h
+
+DOCS = ANNOUNCE CHANGES INSTALL KNOWNBUG LICENSE README TODO Y2KINFO
+writelock:
+	chmod a-w *.[ch35] $(DOCS) scripts/*
+
+# DO NOT DELETE THIS LINE -- make depend depends on it.
+
+png.o png.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngerror.o pngerror.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrio.o pngrio.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwio.o pngwio.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngmem.o pngmem.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngset.o pngset.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngget.o pngget.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngread.o pngread.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrtran.o pngrtran.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngrutil.o pngrutil.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngtrans.o pngtrans.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwrite.o pngwrite.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwtran.o pngwtran.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngwutil.o pngwutil.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+pngpread.o pngpread.pic.o: png.h pngconf.h pnglibconf.h pngpriv.h pngstruct.h pnginfo.h pngdebug.h
+arm/arm_init.o arm/arm_init.o: pngpriv.h
+arm/filter_neon_intrinsics.o arm/filter_neon_intrinsics.pic.o: pngpriv.h
+mips/mips_init.o mips/mips_init.pic.o: pngpriv.h
+mips/filter_msa_intrinsics.o mips/filter_msa_intrinsics.pic.:  pngpriv.h
+intel/intel_init.o intel/intel_init.pic.:  pngpriv.h
+intel/filter_sse2_intrinsics.o intel/filter_sse2_intrinsics.pic.:  pngpriv.h
+powerpc/powerpc_init.o powerpc/powerpc_init.pic.:  pngpriv.h
+powerpc/filter_vsx_intrinsics.o powerpc/filter_vsx_intrinsics.pic.:  pngpriv.h
+
+pngtest.o: png.h pngconf.h pnglibconf.h
diff --git a/scripts/makefile.msys b/scripts/makefile.msys
index c603673..3056542 100644
--- a/scripts/makefile.msys
+++ b/scripts/makefile.msys
@@ -18,7 +18,7 @@
 # Library name:
 LIBNAME = libpng16
 PNGMAJ = 16
-RELEASE = 30
+RELEASE = 31
 
 # Shared library names:
 LIBSO=$(LIBNAME).dll
diff --git a/scripts/makefile.ne12bsd b/scripts/makefile.ne12bsd
index 54f7a6e..01d9727 100644
--- a/scripts/makefile.ne12bsd
+++ b/scripts/makefile.ne12bsd
@@ -17,7 +17,7 @@
 
 LIB=	png16
 SHLIB_MAJOR=	0
-SHLIB_MINOR=	1.6.30
+SHLIB_MINOR=	1.6.31
 SRCS=	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 e296b08..7e39344 100644
--- a/scripts/makefile.netbsd
+++ b/scripts/makefile.netbsd
@@ -17,7 +17,7 @@
 
 LIB=	png
 SHLIB_MAJOR=	16
-SHLIB_MINOR=	1.6.30
+SHLIB_MINOR=	1.6.31
 SRCS=	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.openbsd b/scripts/makefile.openbsd
index e881933..f3f8105 100644
--- a/scripts/makefile.openbsd
+++ b/scripts/makefile.openbsd
@@ -11,7 +11,7 @@
 MANDIR= ${PREFIX}/man/cat
 
 SHLIB_MAJOR=	16
-SHLIB_MINOR=	1.6.30
+SHLIB_MINOR=	1.6.31
 
 LIB=	png
 SRCS=	png.c pngerror.c pngget.c pngmem.c pngpread.c \
diff --git a/scripts/pnglibconf.dfa b/scripts/pnglibconf.dfa
index 4d4e13b..cd7aaaf 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -741,6 +741,8 @@
 # Ancillary chunks
 chunk bKGD
 chunk cHRM enables COLORSPACE
+# enable eXIf only after chunk is approved
+chunk eXIf
 chunk gAMA enables GAMMA
 chunk hIST
 chunk iCCP enables COLORSPACE, GAMMA
diff --git a/scripts/pnglibconf.h.prebuilt b/scripts/pnglibconf.h.prebuilt
index da3d835..9b9bbce 100644
--- a/scripts/pnglibconf.h.prebuilt
+++ b/scripts/pnglibconf.h.prebuilt
@@ -1,8 +1,8 @@
-/* libpng 1.6.30 STANDARD API DEFINITION */
+/* libpng 1.6.31 STANDARD API DEFINITION */
 
 /* pnglibconf.h - library build configuration */
 
-/* Libpng version 1.6.30 - June 28, 2017 */
+/* Libpng version 1.6.31 - July 27, 2017 */
 
 /* Copyright (c) 1998-2017 Glenn Randers-Pehrson */
 
@@ -84,6 +84,7 @@
 #define PNG_READ_USER_TRANSFORM_SUPPORTED
 #define PNG_READ_bKGD_SUPPORTED
 #define PNG_READ_cHRM_SUPPORTED
+#define PNG_READ_eXIf_SUPPORTED
 #define PNG_READ_gAMA_SUPPORTED
 #define PNG_READ_hIST_SUPPORTED
 #define PNG_READ_iCCP_SUPPORTED
@@ -153,6 +154,7 @@
 #define PNG_WRITE_WEIGHTED_FILTER_SUPPORTED
 #define PNG_WRITE_bKGD_SUPPORTED
 #define PNG_WRITE_cHRM_SUPPORTED
+#define PNG_WRITE_eXIf_SUPPORTED
 #define PNG_WRITE_gAMA_SUPPORTED
 #define PNG_WRITE_hIST_SUPPORTED
 #define PNG_WRITE_iCCP_SUPPORTED
@@ -170,6 +172,7 @@
 #define PNG_WRITE_zTXt_SUPPORTED
 #define PNG_bKGD_SUPPORTED
 #define PNG_cHRM_SUPPORTED
+#define PNG_eXIf_SUPPORTED
 #define PNG_gAMA_SUPPORTED
 #define PNG_hIST_SUPPORTED
 #define PNG_iCCP_SUPPORTED
diff --git a/scripts/symbols.def b/scripts/symbols.def
index fe90a29..d714cf6 100644
--- a/scripts/symbols.def
+++ b/scripts/symbols.def
@@ -1,4 +1,4 @@
-;Version 1.6.30
+;Version 1.6.31
 ;--------------------------------------------------------------
 ; LIBPNG symbol list as a Win32 DEF file
 ; Contains all the symbols that can be exported from libpng
@@ -250,3 +250,5 @@
  png_get_palette_max @243
  png_set_option @244
  png_image_write_to_memory @245
+ png_get_eXIf @246
+ png_set_eXIf @247