diff --git a/ANNOUNCE b/ANNOUNCE
index 51c3a7ca7..94a3969e9 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 @@ Files available for download:
 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 b8e0f9742..a2f367a5f 100644
--- a/CHANGES
+++ b/CHANGES
@@ -5855,6 +5855,59 @@ Version 1.6.30rc02 [June 25, 2017]
 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 739ce1581..0c72c36dd 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 @@ enable_testing()
 
 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_FRAMEWORK "Build OS X framework" OFF)
 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 @@ endif()
 # 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 ${PNG_POWERPC_VSX} index)
@@ -127,19 +129,62 @@ if(CMAKE_SYSTEM_PROCESSOR MATCHES "^powerpc*" OR
     set(libpng_powerpc_sources
       powerpc/powerpc_init.c
       powerpc/filter_vsx_intrinsics.c)
-
     if(${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 @@ set(libpng_sources
   pngwtran.c
   pngwutil.c
   ${libpng_arm_sources}
+  ${libpng_intel_sources}
+  ${libpng_mips_sources}
   ${libpng_powerpc_sources}
 )
 set(pngtest_sources
@@ -726,12 +773,12 @@ macro(CREATE_SYMLINK SRC_FILE DEST_FILE)
         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 @@ endif(NOT WIN32 OR CYGWIN OR MINGW)
 # 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 @@ if(NOT SKIP_INSTALL_FILES AND NOT SKIP_INSTALL_ALL )
             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 48b125049..e8edb7240 100644
--- a/INSTALL
+++ b/INSTALL
@@ -16,10 +16,11 @@ Contents
       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 @@ library to fail if they call functions not available in your library.
 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 @@ $PREFIX/include directory).  Do not edit pnglibconf.h after you have built
 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 @@ This requires setjmp/longjmp, so you must either build the library
 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 your application fails to find libpng or zlib entries while linking:
   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 9e935787d..1df0cbbdd 100644
--- a/LICENSE
+++ b/LICENSE
@@ -10,7 +10,7 @@ this sentence.
 
 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 65dccaf64..1f68cfa64 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 3b061d6bb..000764cd2 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 706dbf13e..b1fd1585d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -25,7 +25,7 @@ AC_PREREQ([2.68])
 
 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 automake, so the following is not necessary (and is not defined anyway):
 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 @@ AM_CONDITIONAL([DO_INSTALL_LIBPNG_CONFIG],
 # 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 94f9bb1e0..a9bc360dd 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 @@ png_have_neon(png_structp png_ptr)
 
                counter=0;
                state = Feature;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case Feature:
                /* Match 'FEATURE', ASCII case insensitive. */
@@ -75,7 +75,7 @@ png_have_neon(png_structp png_ptr)
 
                /* did not match 'feature' */
                state = SkipLine;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case SkipLine:
             skipLine:
@@ -110,7 +110,7 @@ png_have_neon(png_structp png_ptr)
 
                state = Neon;
                counter = 0;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case Neon:
                /* Look for 'neon' tag */
@@ -122,7 +122,7 @@ png_have_neon(png_structp png_ptr)
                }
 
                state = SkipTag;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case SkipTag:
                /* Skip non-space characters */
diff --git a/contrib/libtests/pngstest.c b/contrib/libtests/pngstest.c
index 30f57a966..0617dbb04 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 @@ compare_two_images(Image *a, Image *b, int via_linear,
        */
       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 @@ compare_two_images(Image *a, Image *b, int via_linear,
                {
                   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 @@ compare_two_images(Image *a, Image *b, int via_linear,
                {
                   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 aba605e2d..7bb33f829 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 @@ get_unknown(display *d, png_infop info_ptr, int after_IDAT)
                   ++(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 b0daa18b1..4dc4f8447 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 @@ transform_info_imp(transform_display *dp, png_structp pp, png_infop pi)
    {
    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 @@ gamma_component_validate(const char *name, const validate_info *vi,
                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 818758715..059503e23 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 6da970ccb..69ffc170e 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 @@ zlib_advance(struct zlib *zlib, png_uint_32 nbytes)
                   endrc = ZLIB_TOO_FAR_BACK;
                   break;
                }
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             default:
                zlib_message(zlib, 0/*stream error*/);
@@ -2570,7 +2569,7 @@ zlib_run(struct zlib *zlib)
                   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 @@ zlib_check(struct file *file, png_uint_32 offset)
             /* 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 @@ read_callback(png_structp png_ptr, png_bytep buffer, size_t count)
                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 a71000fa0..99d2f054a 100644
--- a/example.c
+++ b/example.c
@@ -114,13 +114,13 @@ int main(int argc, const char **argv)
 
          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 b91d8da96..5e8553fbb 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 @@ static __m128i load3(const void* p) {
    /* 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 @@ static void store3(void* p, __m128i v) {
     * 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 @@ void png_read_filter_row_sub3_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_sub3_sse2(png_row_infop row_info, png_bytep row,
       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 @@ void png_read_filter_row_sub4_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_sub4_sse2(png_row_infop row_info, png_bytep row,
       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 @@ void png_read_filter_row_avg3_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_avg3_sse2(png_row_infop row_info, png_bytep row,
       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 @@ void png_read_filter_row_avg4_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_paeth3_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_paeth3_sse2(png_row_infop row_info, png_bytep row,
       /* 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 @@ void png_read_filter_row_paeth4_sse2(png_row_infop row_info, png_bytep row,
     * 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 @@ void png_read_filter_row_paeth4_sse2(png_row_infop row_info, png_bytep row,
       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 6cde89ab0..b81d2a680 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 @@ libpng-manual.txt - A description on how to use and modify libpng
 
  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 @@ in until png_read_end() has read the chunk data following the image.
     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 @@ png_set_rgb_to_gray()).
                      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 @@ your application instead of by libpng, you can use
              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 @@ width, height, bit_depth, and color_type must be the same in each call.
                      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 @@ is an error. Previously this requirement of the PNG specification was not
 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 @@ 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 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 12eb2e2de..345aba1b5 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 @@ libpng \- Portable Network Graphics (PNG) Reference Library 1.6.30
 
 \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 @@ libpng \- Portable Network Graphics (PNG) Reference Library 1.6.30
 
 \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 @@ Following is a copy of the libpng-manual.txt file that accompanies libpng.
 .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 @@ libpng-manual.txt - A description on how to use and modify libpng
 
  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 @@ in until png_read_end() has read the chunk data following the image.
     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 @@ png_set_rgb_to_gray()).
                      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 @@ your application instead of by libpng, you can use
              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 @@ width, height, bit_depth, and color_type must be the same in each call.
                      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 @@ is an error. Previously this requirement of the PNG specification was not
 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 @@ 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 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 @@ the first widely used release:
  ...
  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 @@ possible without all of you.
 
 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 sentence.
 
 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 @@ files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
 
 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 3e7e2c58a..9708e9af2 100644
--- a/libpng.pc.in
+++ b/libpng.pc.in
@@ -6,6 +6,7 @@ includedir=@includedir@/libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@
 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 c7ae9ed04..70992ab6e 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 40688be12..ae5e1d9b4 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 @@ png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask,
    }
 #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 @@ png_get_copyright(png_const_structrp png_ptr)
 #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 @@ png_pow10(int power)
 /* 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 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
              */
             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 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
 
             /* 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 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
                 * 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 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
                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 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
    /* 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 @@ png_fixed(png_const_structrp png_ptr, double fp, png_const_charp text)
  * 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 @@ png_muldiv(png_fixed_point_p res, png_fixed_point a, png_int_32 times,
 
    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 c2c4fdf25..4321416b8 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 @@ extern "C" {
 /* 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 @@ typedef png_unknown_chunk * * png_unknown_chunkpp;
 #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 @@ PNG_EXPORT(99, void, png_data_freer, (png_const_structrp png_ptr,
 #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_EXPORT(233, void, png_set_cHRM_XYZ_fixed, (png_const_structrp png_ptr,
     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 @@ PNG_FIXED_EXPORT(140, void, png_set_gAMA_fixed, (png_const_structrp png_ptr,
 #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 @@ PNG_EXPORT(244, int, png_set_option, (png_structrp png_ptr, int option,
  * 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 f64592acd..af6e80c99 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 00d76f7c0..ad48bfb98 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 @@ png_format_number(png_const_charp start, png_charp end, int format,
          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 @@ png_format_number(png_const_charp start, png_charp end, int format,
          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 141c39333..ace9e6351 100644
--- a/pngget.c
+++ b/pngget.c
@@ -773,6 +773,24 @@ png_get_sPLT(png_const_structrp png_ptr, png_inforp info_ptr,
 }
 #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 361ed8be7..6e6d46a62 100644
--- a/pnginfo.h
+++ b/pnginfo.h
@@ -185,6 +185,11 @@ defined(PNG_READ_BACKGROUND_SUPPORTED)
    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 a062a8da1..ef45ab759 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_INTERNAL_FUNCTION(void,png_handle_cHRM,(png_structrp png_ptr,
     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 106a80588..331ce121c 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 @@ png_create_colormap_entry(png_image_read_control *display,
          {
             case 4:
                entry[afirst ? 0 : 3] = (png_uint_16)alpha;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case 3:
                if (alpha < 65535)
@@ -1905,7 +1905,7 @@ png_create_colormap_entry(png_image_read_control *display,
 
             case 2:
                entry[1 ^ afirst] = (png_uint_16)alpha;
-               /* FALL THROUGH */
+               /* FALLTHROUGH */
 
             case 1:
                if (alpha < 65535)
@@ -1934,6 +1934,7 @@ png_create_colormap_entry(png_image_read_control *display,
          {
             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 @@ png_create_colormap_entry(png_image_read_control *display,
 
             case 2:
                entry[1 ^ afirst] = (png_byte)alpha;
+               /* FALLTHROUGH */
             case 1:
                entry[afirst] = (png_byte)green;
                break;
@@ -2861,7 +2863,7 @@ png_image_read_colormap(png_voidp argument)
       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 @@ png_image_read_colormapped(png_voidp argument)
             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 3886833af..9a30ddf22 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 @@ png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
       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 @@ png_init_rgb_transformations(png_structrp png_ptr)
             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 f60545bf9..7fe5cd1de 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 @@ png_handle_bKGD(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
 }
 #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 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
          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 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
 
          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 fb495ac3f..998473557 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 @@ png_set_cHRM_XYZ(png_const_structrp png_ptr, png_inforp info_ptr, double red_X,
 
 #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 749d7e35b..44b79dea7 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -479,5 +479,8 @@ struct png_struct_def
    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 d2938d183..bdd37db4b 100644
--- a/pngtest.c
+++ b/pngtest.c
@@ -1192,6 +1192,14 @@ test_one_file(PNG_CONST char *inname, PNG_CONST char *outname)
       }
    }
 #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 @@ test_one_file(PNG_CONST char *inname, PNG_CONST char *outname)
       }
    }
 #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 @@ main(void)
 #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 cb3fef4cf..66df0c4e6 100644
Binary files a/pngtest.png and b/pngtest.png differ
diff --git a/pngtrans.c b/pngtrans.c
index 6c8c64623..326ac33f0 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 07088ee75..70d47c4ca 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 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
          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 @@ png_image_set_PLTE(png_image_write_control *display)
                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 @@ png_image_set_PLTE(png_image_write_control *display)
                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 dd800586b..348bb524d 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -1473,6 +1473,37 @@ png_write_bKGD(png_structrp png_ptr, png_const_color_16p back, int color_type)
 }
 #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 1856022e2..38c159cce 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 df9c4d607..f3fa10110 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 24b122836..76e70e644 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 @@ pnglibconf.h.prebuilt       =>  Stores configuration settings
  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 f474f1f3f..aedaec8b8 100644
--- a/scripts/def.c
+++ b/scripts/def.c
@@ -21,7 +21,7 @@ PNG_DFN "OS2 DESCRIPTION "PNG image compression library""
 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 4efbab7e7..9e7d952ba 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 08365a4e7..8210520e0 100644
--- a/scripts/libpng.pc.in
+++ b/scripts/libpng.pc.in
@@ -5,6 +5,6 @@ includedir=@includedir@/libpng16
 
 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 6043845bb..ef17dab71 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 f3f9550b8..8bb5ba70c 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=$(LIBNAME).so
diff --git a/scripts/makefile.linux-opt b/scripts/makefile.linux-opt
new file mode 100644
index 000000000..f93c5457f
--- /dev/null
+++ b/scripts/makefile.linux-opt
@@ -0,0 +1,265 @@
+# makefile for libpng.a and libpng16.so on Linux ELF with gcc
+# Copyright (C) 1998,1999,2002,2006,2008,2010-2014,2017 Greg Roelofs and
+# Glenn Randers-Pehrson
+# Copyright (C) 1996,1997 Andreas Dilger
+#
+# This code is released under the libpng license.
+# For conditions of distribution and use, see the disclaimer
+# and license in png.h
+
+# Library name:
+LIBNAME = libpng16
+PNGMAJ = 16
+RELEASE = 31
+
+# Shared library names:
+LIBSO=$(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 c603673da..305654298 100644
--- a/scripts/makefile.msys
+++ b/scripts/makefile.msys
@@ -18,7 +18,7 @@ exec_prefix=$(prefix)
 # Library name:
 LIBNAME = libpng16
 PNGMAJ = 16
-RELEASE = 30
+RELEASE = 31
 
 # Shared library names:
 LIBSO=$(LIBNAME).dll
diff --git a/scripts/makefile.ne12bsd b/scripts/makefile.ne12bsd
index 54f7a6ed4..01d972705 100644
--- a/scripts/makefile.ne12bsd
+++ b/scripts/makefile.ne12bsd
@@ -17,7 +17,7 @@ INCSDIR=${LOCALBASE}/include/libpng16
 
 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 e296b08be..7e393444e 100644
--- a/scripts/makefile.netbsd
+++ b/scripts/makefile.netbsd
@@ -17,7 +17,7 @@ INCSDIR=${LOCALBASE}/include
 
 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 e8819333b..f3f810565 100644
--- a/scripts/makefile.openbsd
+++ b/scripts/makefile.openbsd
@@ -11,7 +11,7 @@ LIBDIR=	${PREFIX}/lib
 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 4d4e13b16..cd7aaafd9 100644
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -741,6 +741,8 @@ setting IDAT_READ_SIZE default PNG_ZBUF_SIZE
 # 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 da3d8359f..9b9bbcea1 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 fe90a29a3..d714cf6ce 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 @@ EXPORTS
  png_get_palette_max @243
  png_set_option @244
  png_image_write_to_memory @245
+ png_get_eXIf @246
+ png_set_eXIf @247