[libpng16] Imported from libpng-1.6.18beta02.tar

[libpng16] Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler
(Bug report by Viktor Szaka'ts).
2025-07-10 18:04:09 +02:00 · 2015-04-26 16:38:10 -05:00 · 2015-04-01 12:06:01 -05:00 · 2015-04-01 08:24:26 -05:00 · 2015-04-01 08:24:14 -05:00 · 2015-03-30 21:38:31 -05:00
51 changed files with 688 additions and 381 deletions
--- a/60
+++ b/60
@@ -1,4 +1,4 @@
-Libpng 1.6.17beta05 - February 23, 2015
+Libpng 1.6.18beta02 - April 26, 2015

 This is not intended to be a public release.  It will be replaced
 within a few weeks by a public version or by another test version.
@@ -8,55 +8,35 @@ Files available for download:
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script

-   1.6.17beta05.tar.xz (LZMA-compressed, recommended)
-   1.6.17beta05.tar.gz
+   1.6.18beta02.tar.xz (LZMA-compressed, recommended)
+   1.6.18beta02.tar.gz

 Source files with CRLF line endings (for Windows), without the
 "configure" script

-   lp1617b05.7z  (LZMA-compressed, recommended)
-   lp1617b05.zip
+   lp1618b02.7z  (LZMA-compressed, recommended)
+   lp1618b02.zip

 Other information:

-   1.6.17beta05-README.txt
-   1.6.17beta05-LICENSE.txt
-   libpng-1.6.17beta05-*.asc (armored detached GPG signatures)
+   1.6.18beta02-README.txt
+   1.6.18beta02-LICENSE.txt
+   libpng-1.6.18beta02-*.asc (armored detached GPG signatures)

-Changes since the last public release (1.6.16):
+Changes since the last public release (1.6.17):

-Version 1.6.17beta01 [January 29, 2015]
-  Removed duplicate PNG_SAFE_LIMITS_SUPPORTED handling from pngconf.h
-  Corrected the width limit calculation in png_check_IHDR().
-  Removed user limits from pngfix. Also pass NULL pointers to
-    png_read_row to skip the unnecessary row de-interlace stuff.
-  Added testing of png_set_packing() to pngvalid.c
-  Regenerated configure scripts in the *.tar distributions with libtool-2.4.4
-  Implement previously untested cases of libpng transforms in pngvalid.c
-  Fixed byte order in 2-byte filler, in png_do_read_filler().
-  Made the check for out-of-range values in png_set_tRNS() detect
-    values that are exactly 2^bit_depth, and work on 16-bit platforms.
-  Merged some parts of libpng-1.6.17beta01 and libpng-1.7.0beta47.
-  Added #ifndef __COVERITY__ where needed in png.c, pngrutil.c and
-    pngset.c to avoid warnings about dead code.
+Version 1.6.18beta01 [April 1, 2015]
+  Removed PNG_SET_CHUNK_[CACHE|MALLOC]_LIMIT_SUPPORTED macros.  They
+    have been combined with PNG_SET_USER_LIMITS_SUPPORTED (resolves
+    bug report by Andrew Church).
+  Fixed rgb_to_gray checks and added tRNS checks to pngvalid.c.  This
+    fixes some arithmetic errors that caused some tests to fail on
+    some 32-bit platforms (Bug reports by Peter Breitenlohner [i686]
+    and Petr Gajdos [i586]).

-Version 1.6.17beta02 [February 7, 2015]
-  Work around one more Coverity-scan dead-code warning.
-  Do not build png_product2() when it is unused.
-
-Version 1.6.17beta03 [February 17, 2015]
-  Display user limits in the output from pngtest.
-  Eliminated the PNG_SAFE_LIMITS macro and restored the 1-million-column
-    and 1-million-row default limits in pnglibconf.dfa, that can be reset
-    by the user at build time or run time.  This provides a more robust
-    defense against DOS and as-yet undiscovered overflows.
-
-Version 1.6.17beta04 [February 21, 2015]
-  Added PNG_WRITE_CUSTOMIZE_COMPRESSION_SUPPORTED macro, on by default.
-  Allow user to call png_get_IHDR() with NULL arguments (Reuben Hawkins).
-  Rebuilt configure scripts with automake-1.15 and libtool-2.4.6
-
-Version 1.6.17beta05 [February 23, 2015]
+Version 1.6.18beta02 [April 26, 2015]
+  Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler
+    (Bug report by Viktor Szaka'ts).

 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
--- a/63
+++ b/63
@@ -2102,7 +2102,7 @@ Version 1.4.0beta24 [July 25, 2008]
    png_decompress_chunk(), and remove "chunkdata" from parameter list.
  Put a call to png_check_chunk_name() in png_read_chunk_header().
  Revised png_check_chunk_name() to reject a name with a lowercase 3rd byte.
-  Removed two calls to png_check_chunk_name() occuring later in the process.
+  Removed two calls to png_check_chunk_name() occurring later in the process.
  Define PNG_NO_ERROR_NUMBERS by default in pngconf.h

 Version 1.4.0beta25 [July 30, 2008]
@@ -5140,6 +5140,8 @@ Version 1.6.17beta01 [January 29, 2015]
  Merged some parts of libpng-1.6.17beta01 and libpng-1.7.0beta47.
  Added #ifndef __COVERITY__ where needed in png.c, pngrutil.c and
    pngset.c to avoid warnings about dead code.
+  Added "& 0xff" to many instances of expressions that are typecast
+    to (png_byte), to avoid Coverity warnings.

 Version 1.6.17beta02 [February 7, 2015]
  Work around one more Coverity-scan dead-code warning.
@@ -5157,7 +5159,64 @@ Version 1.6.17beta04 [February 21, 2015]
  Allow user to call png_get_IHDR() with NULL arguments (Reuben Hawkins).
  Rebuilt configure scripts with automake-1.15 and libtool-2.4.6

-Version 1.6.17beta05 [February 23, 2015]
+Version 1.6.17beta05 [February 25, 2015]
+  Restored compiling of png_reciprocal2 with PNG_NO_16BIT.
+
+Version 1.6.17beta06 [February 27, 2015]
+  Moved png_set_filter() prototype into a PNG_WRITE_SUPPORTED block
+    of png.h.
+  Avoid runtime checks when converting integer to png_byte with
+    Visual Studio (Sergey Kosarevsky)
+
+Version 1.6.17rc01 [March 4, 2015]
+  No changes.
+
+Version 1.6.17rc02 [March 9, 2015]
+  Removed some comments that the configure script did not handle
+    properly from scripts/pnglibconf.dfa and pnglibconf.h.prebuilt.
+  Free the unknown_chunks structure even when it contains no data.
+
+Version 1.6.17rc03 [March 12, 2015]
+  Updated CMakeLists.txt to add OSX framework, change YES/NO to ON/OFF
+    for consistency, and remove some useless tests (Alexey Petruchik).
+
+Version 1.6.17rc04 [March 16, 2015]
+  Remove pnglibconf.h, pnglibconf.c, and pnglibconf.out instead of
+    pnglibconf.* in "make clean" (Cosmin).
+  Fix bug in calculation of maxbits, in png_write_sBIT, introduced
+    in libpng-1.6.17beta01 (John Bowler).
+
+Version 1.6.17rc05 [March 21, 2015]
+  Define PNG_FILTER_* and PNG_FILTER_VALUE_* in png.h even when WRITE
+    is not supported (John Bowler).  This fixes an error introduced in
+    libpng-1.6.17beta06.
+  Reverted "& 0xff" additions of version 1.6.17beta01. Libpng passes
+    the Coverity scan without them.
+
+Version 1.6.17rc06 [March 23, 2015]
+  Remove pnglibconf.dfn and pnglibconf.pre with "make clean".
+  Reformatted some "&0xff" instances to "& 0xff".
+  Fixed simplified 8-bit-linear to sRGB alpha. The calculated alpha
+    value was wrong.  It's not clear if this affected the final stored
+    value; in the obvious code path the upper and lower 8-bits of the
+    alpha value were identical and the alpha was truncated to 8-bits
+    rather than dividing by 257 (John Bowler).
+
+Version 1.6.17 [March 26, 2015]
+  No changes.
+
+Version 1.6.18beta01 [April 1, 2015]
+  Removed PNG_SET_CHUNK_[CACHE|MALLOC]_LIMIT_SUPPORTED macros.  They
+    have been combined with PNG_SET_USER_LIMITS_SUPPORTED (resolves
+    bug report by Andrew Church).
+  Fixed rgb_to_gray checks and added tRNS checks to pngvalid.c.  This
+    fixes some arithmetic errors that caused some tests to fail on
+    some 32-bit platforms (Bug reports by Peter Breitenlohner [i686]
+    and Petr Gajdos [i586]).
+
+Version 1.6.18beta02 [April 26, 2015]
+  Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler
+    (Bug report by Viktor Szaka'ts).

 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 # CMakeLists.txt

-# Copyright (C) 2007-2014 Glenn Randers-Pehrson
+# Copyright (C) 2007-2015 Glenn Randers-Pehrson

 # This code is released under the libpng license.
 # For conditions of distribution and use, see the disclaimer
@@ -16,7 +16,7 @@ enable_testing()

 set(PNGLIB_MAJOR 1)
 set(PNGLIB_MINOR 6)
-set(PNGLIB_RELEASE 17)
+set(PNGLIB_RELEASE 18)
 set(PNGLIB_NAME libpng${PNGLIB_MAJOR}${PNGLIB_MINOR})
 set(PNGLIB_VERSION ${PNGLIB_MAJOR}.${PNGLIB_MINOR}.${PNGLIB_RELEASE})

@@ -30,8 +30,7 @@ if(NOT WIN32)
    PATHS /usr/lib /usr/local/lib
  )
  if(NOT M_LIBRARY)
-    message(STATUS
-      "math library 'libm' not found - floating point support disabled")
+    message(STATUS "math lib 'libm' not found; floating point support disabled")
  endif()
 else()
  # not needed on windows
@@ -39,22 +38,14 @@ else()
 endif()

 # COMMAND LINE OPTIONS
-if(DEFINED PNG_SHARED)
-  option(PNG_SHARED "Build shared lib" ${PNG_SHARED})
-else()
-  option(PNG_SHARED "Build shared lib" ON)
-endif()
-if(DEFINED PNG_STATIC)
-  option(PNG_STATIC "Build static lib" ${PNG_STATIC})
-else()
-  option(PNG_STATIC "Build static lib" ON)
-endif()
-
-option(PNG_TESTS  "Build libpng tests" YES)
+option(PNG_SHARED "Build shared lib" ON)
+option(PNG_STATIC "Build static lib" ON)
+option(PNG_TESTS  "Build libpng tests" ON)

 # Many more configuration options could be added here
-option(PNG_DEBUG         "Build with debug output" NO)
-option(PNGARG            "Disable ANSI-C prototypes" NO)
+option(PNG_FRAMEWORK "Build OS X framework" OFF)
+option(PNG_DEBUG     "Build with debug output" OFF)
+option(PNGARG        "Disable ANSI-C prototypes" OFF)

 # SET LIBNAME
 set(PNG_LIB_NAME png${PNGLIB_MAJOR}${PNGLIB_MINOR})
@@ -134,7 +125,7 @@ if(PNG_SHARED)
 endif()

 if(PNG_STATIC)
-# does not work without changing name
+  # does not work without changing name
  set(PNG_LIB_NAME_STATIC ${PNG_LIB_NAME}_static)
  add_library(${PNG_LIB_NAME_STATIC} STATIC ${libpng_sources})
  list(APPEND PNG_LIB_TARGETS ${PNG_LIB_NAME_STATIC})
@@ -145,10 +136,27 @@ if(PNG_STATIC)
  target_link_libraries(${PNG_LIB_NAME_STATIC} ${ZLIB_LIBRARY} ${M_LIBRARY})
 endif()

+if(PNG_FRAMEWORK)
+  set(PNG_LIB_NAME_FRAMEWORK ${PNG_LIB_NAME}_framework)
+  add_library(${PNG_LIB_NAME_FRAMEWORK} SHARED ${libpng_sources})
+  list(APPEND PNG_LIB_TARGETS ${PNG_LIB_NAME_FRAMEWORK})
+  set_target_properties(${PNG_LIB_NAME_FRAMEWORK} PROPERTIES
+    FRAMEWORK TRUE
+    FRAMEWORK_VERSION ${PNGLIB_VERSION}
+    MACOSX_FRAMEWORK_SHORT_VERSION_STRING ${PNGLIB_MAJOR}.${PNGLIB_MINOR}
+    MACOSX_FRAMEWORK_BUNDLE_VERSION ${PNGLIB_VERSION}
+    MACOSX_FRAMEWORK_IDENTIFIER org.libpng.libpng
+    XCODE_ATTRIBUTE_INSTALL_PATH "@rpath"
+    PUBLIC_HEADER "${libpng_public_hdrs}"
+    OUTPUT_NAME png)
+  target_link_libraries(${PNG_LIB_NAME_FRAMEWORK} ${ZLIB_LIBRARY} ${M_LIBRARY})
+endif()
+
 if(NOT PNG_LIB_TARGETS)
  message(SEND_ERROR
    "No library variant selected to build. "
-    "Please enable at least one of the following options: PNG_STATIC, PNG_SHARED")
+    "Please enable at least one of the following options: "
+    " PNG_STATIC, PNG_SHARED, PNG_FRAMEWORK")
 endif()

 if(PNG_SHARED AND WIN32)
@@ -253,7 +261,7 @@ endif(NOT WIN32 OR CYGWIN OR MINGW)
 # SET UP LINKS
 if(PNG_SHARED)
  set_target_properties(${PNG_LIB_NAME} PROPERTIES
-#   VERSION 16.${PNGLIB_RELEASE}.1.6.17beta05
+#   VERSION 16.${PNGLIB_RELEASE}.1.6.18beta02
    VERSION 16.${PNGLIB_RELEASE}.0
    SOVERSION 16
    CLEAN_DIRECT_OUTPUT 1)
@@ -284,7 +292,8 @@ if(NOT SKIP_INSTALL_LIBRARIES AND NOT SKIP_INSTALL_ALL )
      ${PNG_EXPORT_RULE}
      RUNTIME DESTINATION bin
      LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
-      ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR})
+      ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+      FRAMEWORK DESTINATION ${CMAKE_INSTALL_LIBDIR})

  if(PNG_SHARED)
    # Create a symlink for libpng.dll.a => libpng16.dll.a on Cygwin
--- a/2
+++ b/2
@@ -189,7 +189,7 @@ run "make install".
 VIII. Configuring libpng for 16-bit platforms

 You will want to look into zconf.h to tell zlib (and thus libpng) that
-it cannot allocate more then 64K at a time.  Even if you can, the memory
+it cannot allocate more than 64K at a time.  Even if you can, the memory
 won't be accessible.  So limit zlib and libpng to 64K by defining MAXSEG_64K.

 IX. Configuring for DOS
--- a/4
+++ b/4
@@ -10,7 +10,7 @@ this sentence.

 This code is released under the libpng license.

-libpng versions 1.2.6, August 15, 2004, through 1.6.17beta05, February 23, 2015, are
+libpng versions 1.2.6, August 15, 2004, through 1.6.18beta02, April 26, 2015, are
 Copyright (c) 2004, 2006-2015 Glenn Randers-Pehrson, and are
 distributed according to the same disclaimer and license as libpng-1.2.5
 with the following individual added to the list of Contributing Authors
@@ -108,4 +108,4 @@ certification mark of the Open Source Initiative.

 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-February 23, 2015
+April 26, 2015
--- a/Makefile.am
+++ b/Makefile.am
@@ -129,11 +129,12 @@ EXTRA_DIST= \
 	$(TESTS) $(XFAIL_TESTS) tests/pngstest \
 	CMakeLists.txt example.c libpng-manual.txt

-SCRIPT_CLEANFILES=scripts/*.out scripts/*.chk scripts/pnglibconf.c
+SCRIPT_CLEANFILES=scripts/*.out scripts/*.chk

 CLEANFILES= *.tf? pngout.png libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@.pc \
 	libpng@PNGLIB_MAJOR@@PNGLIB_MINOR@-config libpng.vers libpng.sym \
-	check.new pnglibconf.* pngprefix.h symbols.new pngtest-log.txt \
+	check.new pnglibconf.h pngprefix.h symbols.new pngtest-log.txt \
+	pnglibconf.out pnglibconf.c pnglibconf.pre pnglibconf.dfn \
 	$(SCRIPT_CLEANFILES)

 MAINTAINERCLEANFILES = Makefile.in aclocal.m4 config.guess config.h.in \
--- a/2
+++ b/2
@@ -1,4 +1,4 @@
-README for libpng version 1.6.17beta05 - February 23, 2015 (shared library 16.0)
+README for libpng version 1.6.18beta02 - April 26, 2015 (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.
--- a/autogen.sh
+++ b/autogen.sh
@@ -73,8 +73,9 @@ done
 # present bad things are happening.
 #
 # The autotools generated files:
-libpng_autotools_files="Makefile.in aclocal.m4 config.guess config.h.in\
-   config.sub configure depcomp install-sh ltmain.sh missing test-driver"
+libpng_autotools_files="Makefile.in aclocal.m4 config.guess config.h.in
+   config.h.in~ config.sub configure depcomp install-sh ltmain.sh missing\
+   test-driver"
 #
 # Files generated by versions of configue >2.68 or automake >1.13 (i.e. later
 # versions than those required by configure.ac):
--- a/configure.ac
+++ b/configure.ac
@@ -18,7 +18,7 @@ AC_PREREQ([2.68])

 dnl Version number stuff here:

-AC_INIT([libpng],[1.6.17beta05],[png-mng-implement@lists.sourceforge.net])
+AC_INIT([libpng],[1.6.18beta02],[png-mng-implement@lists.sourceforge.net])
 AC_CONFIG_MACRO_DIR([scripts])

 # libpng does not follow GNU file name conventions (hence 'foreign')
@@ -39,10 +39,10 @@ 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=1.6.17beta05
+PNGLIB_VERSION=1.6.18beta02
 PNGLIB_MAJOR=1
 PNGLIB_MINOR=6
-PNGLIB_RELEASE=17
+PNGLIB_RELEASE=18

 dnl End of version number stuff

--- a/contrib/libtests/pngunknown.c
+++ b/contrib/libtests/pngunknown.c
@@ -1242,4 +1242,4 @@ main(void)
   /* So the test is skipped: */
   return 77;
 }
-#endif /* SET_UNKNOWN_CHUNKS && READ*/
+#endif /* SET_UNKNOWN_CHUNKS && READ */
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -258,7 +258,7 @@ make_four_random_bytes(png_uint_32* seed, png_bytep bytes)
   make_random_bytes(seed, bytes, 4);
 }

-#ifdef PNG_READ_SUPPORTED
+#if defined PNG_READ_SUPPORTED || defined PNG_WRITE_tRNS_SUPPORTED
 static void
 randomize(void *pv, size_t size)
 {
@@ -267,7 +267,9 @@ randomize(void *pv, size_t size)
 }

 #define RANDOMIZE(this) randomize(&(this), sizeof (this))
+#endif /* READ || WRITE_tRNS */

+#ifdef PNG_READ_SUPPORTED
 static unsigned int
 random_mod(unsigned int max)
 {
@@ -295,7 +297,8 @@ random_choice(void)
 /* A numeric ID based on PNG file characteristics.  The 'do_interlace' field
 * simply records whether pngvalid did the interlace itself or whether it
 * was done by libpng.  Width and height must be less than 256.  'palette' is an
- * index of the palette to use for formats with a palette (0 otherwise.)
+ * index of the palette to use for formats with a palette otherwise a boolean
+ * indicating if a tRNS chunk was generated.
 */
 #define FILEID(col, depth, palette, interlace, width, height, do_interlace) \
   ((png_uint_32)((col) + ((depth)<<3) + ((palette)<<8) + ((interlace)<<13) + \
@@ -316,12 +319,16 @@ standard_name(char *buffer, size_t bufsize, size_t pos, png_byte colour_type,
    png_uint_32 w, png_uint_32 h, int do_interlace)
 {
   pos = safecat(buffer, bufsize, pos, colour_types[colour_type]);
-   if (npalette > 0)
+   if (colour_type == 3) /* must have a palette */
   {
      pos = safecat(buffer, bufsize, pos, "[");
      pos = safecatn(buffer, bufsize, pos, npalette);
      pos = safecat(buffer, bufsize, pos, "]");
   }
+
+   else if (npalette != 0)
+      pos = safecat(buffer, bufsize, pos, "+tRNS");
+
   pos = safecat(buffer, bufsize, pos, " ");
   pos = safecatn(buffer, bufsize, pos, bit_depth);
   pos = safecat(buffer, bufsize, pos, " bit");
@@ -378,25 +385,32 @@ standard_name_from_id(char *buffer, size_t bufsize, size_t pos, png_uint_32 id)

 static int
 next_format(png_bytep colour_type, png_bytep bit_depth,
-   unsigned int* palette_number, int no_low_depth_gray)
+   unsigned int* palette_number, int low_depth_gray, int tRNS)
 {
   if (*bit_depth == 0)
   {
      *colour_type = 0;
-      if (no_low_depth_gray)
-         *bit_depth = 8;
-      else
+      if (low_depth_gray)
         *bit_depth = 1;
+      else
+         *bit_depth = 8;
      *palette_number = 0;
      return 1;
   }

-   if (*colour_type == 3)
+   if  (*colour_type < 4/*no alpha channel*/)
   {
-      /* Add multiple palettes for colour type 3. */
-      if (++*palette_number < PALETTE_COUNT(*bit_depth))
+      /* Add multiple palettes for colour type 3, one image with tRNS
+       * and one without for other non-alpha formats:
+       */
+      unsigned int pn = ++*palette_number;
+      png_byte ct = *colour_type;
+
+      if (((ct == 0/*GRAY*/ || ct/*RGB*/ == 2) && tRNS && pn < 2) ||
+          (ct == 3/*PALETTE*/ && pn < PALETTE_COUNT(*bit_depth)))
         return 1;

+      /* No: next bit depth */
      *palette_number = 0;
   }

@@ -1959,6 +1973,7 @@ typedef struct png_modifier

   /* Run tests on reading with a combination of transforms, */
   unsigned int             test_transform :1;
+   unsigned int             test_tRNS :1; /* Includes tRNS images */

   /* When to use the use_input_precision option, this controls the gamma
    * validation code checks.  If set any value that is within the transformed
@@ -1990,6 +2005,16 @@ typedef struct png_modifier
   unsigned int             test_gamma_expand16 :1;
   unsigned int             test_exhaustive :1;

+   /* Whether or not to run the low-bit-depth grayscale tests.  This fail on
+    * gamma images in some cases because of gross inaccuracies in the grayscale
+    * gamma handling for low bit depth.
+    */
+   unsigned int             test_lbg :1;
+   unsigned int             test_lbg_gamma_threshold :1;
+   unsigned int             test_lbg_gamma_transform :1;
+   unsigned int             test_lbg_gamma_sbit :1;
+   unsigned int             test_lbg_gamma_composition :1;
+
   unsigned int             log :1;   /* Log max error */

   /* Buffer information, the buffer size limits the size of the chunks that can
@@ -2042,6 +2067,11 @@ modifier_init(png_modifier *pm)
   pm->test_standard = 0;
   pm->test_size = 0;
   pm->test_transform = 0;
+#  ifdef PNG_WRITE_tRNS_SUPPORTED
+      pm->test_tRNS = 1;
+#  else
+      pm->test_tRNS = 0;
+#  endif
   pm->use_input_precision = 0;
   pm->use_input_precision_sbit = 0;
   pm->use_input_precision_16to8 = 0;
@@ -2054,6 +2084,11 @@ modifier_init(png_modifier *pm)
   pm->test_gamma_background = 0;
   pm->test_gamma_alpha_mode = 0;
   pm->test_gamma_expand16 = 0;
+   pm->test_lbg = 1;
+   pm->test_lbg_gamma_threshold = 1;
+   pm->test_lbg_gamma_transform = 1;
+   pm->test_lbg_gamma_sbit = 1;
+   pm->test_lbg_gamma_composition = 1;
   pm->test_exhaustive = 0;
   pm->log = 0;

@@ -3192,6 +3227,45 @@ init_standard_palette(png_store *ps, png_structp pp, png_infop pi, int npalette,
   }
 }

+#ifdef PNG_WRITE_tRNS_SUPPORTED
+static void
+set_random_tRNS(png_structp pp, png_infop pi, PNG_CONST png_byte colour_type,
+   PNG_CONST int bit_depth)
+{
+   /* To make this useful the tRNS color needs to match at least one pixel.
+    * Random values are fine for gray, including the 16-bit case where we know
+    * that the test image contains all the gray values.  For RGB we need more
+    * method as only 65536 different RGB values are generated.
+    */
+   png_color_16 tRNS;
+   const png_uint_16 mask = (png_uint_16)((1U << bit_depth)-1);
+
+   RANDOMIZE(tRNS);
+
+   if (colour_type & 2/*RGB*/)
+   {
+      if (bit_depth == 8)
+      {
+         tRNS.blue = tRNS.red ^ tRNS.green;
+         tRNS.red &= mask;
+         tRNS.green &= mask;
+         tRNS.blue &= mask;
+      }
+
+      else /* bit_depth == 16 */
+      {
+         tRNS.green = (png_uint_16)(tRNS.red * 257);
+         tRNS.blue = (png_uint_16)(tRNS.green * 17);
+      }
+   }
+
+   else
+      tRNS.gray &= mask;
+
+   png_set_tRNS(pp, pi, NULL, 0, &tRNS);
+}
+#endif
+
 /* The number of passes is related to the interlace type. There was no libpng
 * API to determine this prior to 1.5, so we need an inquiry function:
 */
@@ -3525,6 +3599,11 @@ make_transform_image(png_store* PNG_CONST ps, png_byte PNG_CONST colour_type,
      if (colour_type == 3) /* palette */
         init_standard_palette(ps, pp, pi, 1U << bit_depth, 1/*do tRNS*/);

+#     ifdef PNG_WRITE_tRNS_SUPPORTED
+         else if (palette_number)
+            set_random_tRNS(pp, pi, colour_type, bit_depth);
+#     endif
+
      png_write_info(pp, pi);

      if (png_get_rowbytes(pp, pi) !=
@@ -3598,19 +3677,20 @@ make_transform_image(png_store* PNG_CONST ps, png_byte PNG_CONST colour_type,
 }

 static void
-make_transform_images(png_store *ps)
+make_transform_images(png_modifier *pm)
 {
   png_byte colour_type = 0;
   png_byte bit_depth = 0;
   unsigned int palette_number = 0;

   /* This is in case of errors. */
-   safecat(ps->test, sizeof ps->test, 0, "make standard images");
+   safecat(pm->this.test, sizeof pm->this.test, 0, "make standard images");

   /* Use next_format to enumerate all the combinations we test, including
-    * generating multiple low bit depth palette images.
+    * generating multiple low bit depth palette images. Non-A images (palette
+    * and direct) are created with and without tRNS chunks.
    */
-   while (next_format(&colour_type, &bit_depth, &palette_number, 0))
+   while (next_format(&colour_type, &bit_depth, &palette_number, 1, 1))
   {
      int interlace_type;

@@ -3621,7 +3701,7 @@ make_transform_images(png_store *ps)

         standard_name(name, sizeof name, 0, colour_type, bit_depth,
            palette_number, interlace_type, 0, 0, 0);
-         make_transform_image(ps, colour_type, bit_depth, palette_number,
+         make_transform_image(&pm->this, colour_type, bit_depth, palette_number,
            interlace_type, name);
      }
   }
@@ -4287,6 +4367,7 @@ typedef struct standard_display
   size_t      cbRow;          /* Bytes in a row of the output image */
   int         do_interlace;   /* Do interlacing internally */
   int         is_transparent; /* Transparency information was present. */
+   int         has_tRNS;       /* color type GRAY or RGB with a tRNS chunk. */
   int         speed;          /* Doing a speed test */
   int         use_update_info;/* Call update_info, not start_image */
   struct
@@ -4619,14 +4700,14 @@ standard_info_part1(standard_display *dp, png_structp pp, png_infop pi)
         case 0:
            dp->transparent.red = dp->transparent.green = dp->transparent.blue =
               trans_color->gray;
-            dp->is_transparent = 1;
+            dp->has_tRNS = 1;
            break;

         case 2:
            dp->transparent.red = trans_color->red;
            dp->transparent.green = trans_color->green;
            dp->transparent.blue = trans_color->blue;
-            dp->is_transparent = 1;
+            dp->has_tRNS = 1;
            break;

         case 3:
@@ -5518,7 +5599,7 @@ image_pixel_add_alpha(image_pixel *this, PNG_CONST standard_display *display)
      if (this->colour_type == PNG_COLOR_TYPE_GRAY)
      {
         if (this->bit_depth < 8)
-            this->bit_depth = 8;
+            this->bit_depth = this->sample_depth = 8;

         if (this->have_tRNS)
         {
@@ -5553,9 +5634,11 @@ image_pixel_add_alpha(image_pixel *this, PNG_CONST standard_display *display)
               this->alphaf = 0;
            else
               this->alphaf = 1;
-
-            this->colour_type = PNG_COLOR_TYPE_RGB_ALPHA;
         }
+         else
+            this->alphaf = 1;
+
+         this->colour_type = PNG_COLOR_TYPE_RGB_ALPHA;
      }

      /* The error in the alpha is zero and the sBIT value comes from the
@@ -5848,8 +5931,9 @@ transform_info_imp(transform_display *dp, png_structp pp, png_infop pi)
   /* If png_set_filler is in action then fake the output color type to include
    * an alpha channel where appropriate.
    */
-   if (dp->output_bit_depth >= 8 && (dp->output_colour_type == PNG_COLOR_TYPE_RGB ||
-       dp->output_colour_type == PNG_COLOR_TYPE_GRAY) && dp->this.filler)
+   if (dp->output_bit_depth >= 8 &&
+       (dp->output_colour_type == PNG_COLOR_TYPE_RGB ||
+        dp->output_colour_type == PNG_COLOR_TYPE_GRAY) && dp->this.filler)
       dp->output_colour_type |= 4;

   /* Validate the combination of colour type and bit depth that we are getting
@@ -6372,6 +6456,13 @@ image_transform_png_set_tRNS_to_alpha_set(PNG_CONST image_transform *this,
   transform_display *that, png_structp pp, png_infop pi)
 {
   png_set_tRNS_to_alpha(pp);
+
+   /* If there was a tRNS chunk that would get expanded and add an alpha
+    * channel is_transparent must be updated:
+    */
+   if (that->this.has_tRNS)
+      that->this.is_transparent = 1;
+
   this->next->set(this->next, that, pp, pi);
 }

@@ -6430,6 +6521,7 @@ image_transform_png_set_gray_to_rgb_set(PNG_CONST image_transform *this,
    transform_display *that, png_structp pp, png_infop pi)
 {
   png_set_gray_to_rgb(pp);
+   /* NOTE: this doesn't result in tRNS expansion. */
   this->next->set(this->next, that, pp, pi);
 }

@@ -6489,6 +6581,10 @@ image_transform_png_set_expand_set(PNG_CONST image_transform *this,
    transform_display *that, png_structp pp, png_infop pi)
 {
   png_set_expand(pp);
+
+   if (that->this.has_tRNS)
+      that->this.is_transparent = 1;
+
   this->next->set(this->next, that, pp, pi);
 }

@@ -6539,6 +6635,7 @@ image_transform_png_set_expand_gray_1_2_4_to_8_set(
    png_infop pi)
 {
   png_set_expand_gray_1_2_4_to_8(pp);
+   /* NOTE: don't expect this to expand tRNS */
   this->next->set(this->next, that, pp, pi);
 }

@@ -6570,6 +6667,11 @@ image_transform_png_set_expand_16_set(PNG_CONST image_transform *this,
    transform_display *that, png_structp pp, png_infop pi)
 {
   png_set_expand_16(pp);
+
+   /* NOTE: at present libpng does SET_EXPAND as well, so tRNS is expanded. */
+   if (that->this.has_tRNS)
+      that->this.is_transparent = 1;
+
   this->next->set(this->next, that, pp, pi);
 }

@@ -6940,14 +7042,14 @@ image_transform_png_set_rgb_to_gray_ini(PNG_CONST image_transform *this,
          * When DIGITIZE is set because a pre-1.7 version of libpng is being
          * tested allow a bigger slack.
          *
-          * NOTE: this magic number was determined by experiment to be 1.25.
-          * There's no great merit to the value below, however it only affects
-          * the limit used for checking for internal calculation errors, not
-          * the actual limit imposed by pngvalid on the output errors.
+          * NOTE: this magic number was determined by experiment to be about
+          * 1.263.  There's no great merit to the value below, however it only
+          * affects the limit used for checking for internal calculation errors,
+          * not the actual limit imposed by pngvalid on the output errors.
          */
         that->pm->limit += pow(
 #        if DIGITIZE
-            1.25
+            1.3
 #        else
            1.0
 #        endif
@@ -7111,7 +7213,8 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
         const unsigned int sample_depth = that->sample_depth;
         const unsigned int calc_depth = (pm->assume_16_bit_calculations ? 16 :
            sample_depth);
-         const unsigned int gamma_depth = (sample_depth == 16 ? 16 :
+         const unsigned int gamma_depth = (sample_depth == 16 ?
+            PNG_MAX_GAMMA_8 :
            (pm->assume_16_bit_calculations ? PNG_MAX_GAMMA_8 : sample_depth));
         int isgray;
         double r, g, b;
@@ -7125,56 +7228,73 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
          * will be identical after this operation if there is only one
          * transform, feel free to delete the png_error checks on this below in
          * the future (this is just me trying to ensure it works!)
+          *
+          * Interval arithmetic is exact, but to implement it it must be
+          * possible to control the floating point implementation rounding mode.
+          * This cannot be done in ANSI-C, so instead I reduce the 'lo' values
+          * by DBL_EPSILON and increase the 'hi' values by the same.
          */
+#        define DD(v,d,r) (digitize(v*(1-DBL_EPSILON), d, r) * (1-DBL_EPSILON))
+#        define DU(v,d,r) (digitize(v*(1+DBL_EPSILON), d, r) * (1+DBL_EPSILON))
+
         r = rlo = rhi = that->redf;
         rlo -= that->rede;
-         rlo = digitize(rlo, calc_depth, 1/*round*/);
+         rlo = DD(rlo, calc_depth, 1/*round*/);
         rhi += that->rede;
-         rhi = digitize(rhi, calc_depth, 1/*round*/);
+         rhi = DU(rhi, calc_depth, 1/*round*/);

         g = glo = ghi = that->greenf;
         glo -= that->greene;
-         glo = digitize(glo, calc_depth, 1/*round*/);
+         glo = DD(glo, calc_depth, 1/*round*/);
         ghi += that->greene;
-         ghi = digitize(ghi, calc_depth, 1/*round*/);
+         ghi = DU(ghi, calc_depth, 1/*round*/);

         b = blo = bhi = that->bluef;
         blo -= that->bluee;
-         blo = digitize(blo, calc_depth, 1/*round*/);
+         blo = DD(blo, calc_depth, 1/*round*/);
         bhi += that->greene;
-         bhi = digitize(bhi, calc_depth, 1/*round*/);
+         bhi = DU(bhi, calc_depth, 1/*round*/);

         isgray = r==g && g==b;

         if (data.gamma != 1)
         {
            PNG_CONST double power = 1/data.gamma;
-            PNG_CONST double abse = calc_depth == 16 ? .5/65535 : .5/255;
+            PNG_CONST double abse = .5/(sample_depth == 16 ? 65535 : 255);

-            /* 'abse' is the absolute error permitted in linear calculations. It
-             * is used here to capture the error permitted in the handling
-             * (undoing) of the gamma encoding.  Once again digitization occurs
-             * to handle the upper and lower bounds of the values.  This is
-             * where the real errors are introduced.
+            /* If a gamma calculation is done it is done using lookup tables of
+             * precision gamma_depth, so the already digitized value above may
+             * need to be further digitized here.
             */
+            if (gamma_depth != calc_depth)
+            {
+               rlo = DD(rlo, gamma_depth, 0/*truncate*/);
+               rhi = DU(rhi, gamma_depth, 0/*truncate*/);
+               glo = DD(glo, gamma_depth, 0/*truncate*/);
+               ghi = DU(ghi, gamma_depth, 0/*truncate*/);
+               blo = DD(blo, gamma_depth, 0/*truncate*/);
+               bhi = DU(bhi, gamma_depth, 0/*truncate*/);
+            }
+
+            /* 'abse' is the error in the gamma table calculation itself. */
            r = pow(r, power);
-            rlo = digitize(pow(rlo, power)-abse, calc_depth, 1);
-            rhi = digitize(pow(rhi, power)+abse, calc_depth, 1);
+            rlo = DD(pow(rlo, power)-abse, calc_depth, 1);
+            rhi = DU(pow(rhi, power)+abse, calc_depth, 1);

            g = pow(g, power);
-            glo = digitize(pow(glo, power)-abse, calc_depth, 1);
-            ghi = digitize(pow(ghi, power)+abse, calc_depth, 1);
+            glo = DD(pow(glo, power)-abse, calc_depth, 1);
+            ghi = DU(pow(ghi, power)+abse, calc_depth, 1);

            b = pow(b, power);
-            blo = digitize(pow(blo, power)-abse, calc_depth, 1);
-            bhi = digitize(pow(bhi, power)+abse, calc_depth, 1);
+            blo = DD(pow(blo, power)-abse, calc_depth, 1);
+            bhi = DU(pow(bhi, power)+abse, calc_depth, 1);
         }

         /* Now calculate the actual gray values.  Although the error in the
          * coefficients depends on whether they were specified on the command
          * line (in which case truncation to 15 bits happened) or not (rounding
          * was used) the maxium error in an individual coefficient is always
-          * 1/32768, because even in the rounding case the requirement that
+          * 2/32768, because even in the rounding case the requirement that
          * coefficients add up to 32768 can cause a larger rounding error.
          *
          * The only time when rounding doesn't occur in 1.5.5 and later is when
@@ -7185,19 +7305,19 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,

         {
            PNG_CONST int do_round = data.gamma != 1 || calc_depth == 16;
-            PNG_CONST double ce = 1. / 32768;
+            PNG_CONST double ce = 2. / 32768;

-            graylo = digitize(rlo * (data.red_coefficient-ce) +
+            graylo = DD(rlo * (data.red_coefficient-ce) +
               glo * (data.green_coefficient-ce) +
-               blo * (data.blue_coefficient-ce), gamma_depth, do_round);
-            if (graylo <= 0)
-               graylo = 0;
+               blo * (data.blue_coefficient-ce), calc_depth, do_round);
+            if (graylo > gray) /* always accept the right answer */
+               graylo = gray;

-            grayhi = digitize(rhi * (data.red_coefficient+ce) +
+            grayhi = DU(rhi * (data.red_coefficient+ce) +
               ghi * (data.green_coefficient+ce) +
-               bhi * (data.blue_coefficient+ce), gamma_depth, do_round);
-            if (grayhi >= 1)
-               grayhi = 1;
+               bhi * (data.blue_coefficient+ce), calc_depth, do_round);
+            if (grayhi < gray)
+               grayhi = gray;
         }

         /* And invert the gamma. */
@@ -7205,11 +7325,25 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
         {
            PNG_CONST double power = data.gamma;

+            /* And this happens yet again, shifting the values once more. */
+            if (gamma_depth != sample_depth)
+            {
+               rlo = DD(rlo, gamma_depth, 0/*truncate*/);
+               rhi = DU(rhi, gamma_depth, 0/*truncate*/);
+               glo = DD(glo, gamma_depth, 0/*truncate*/);
+               ghi = DU(ghi, gamma_depth, 0/*truncate*/);
+               blo = DD(blo, gamma_depth, 0/*truncate*/);
+               bhi = DU(bhi, gamma_depth, 0/*truncate*/);
+            }
+
            gray = pow(gray, power);
-            graylo = digitize(pow(graylo, power), sample_depth, 1);
-            grayhi = digitize(pow(grayhi, power), sample_depth, 1);
+            graylo = DD(pow(graylo, power), sample_depth, 1);
+            grayhi = DU(pow(grayhi, power), sample_depth, 1);
         }

+#        undef DD
+#        undef DU
+
         /* Now the error can be calculated.
          *
          * If r==g==b because there is no overall gamma correction libpng
@@ -7260,16 +7394,28 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
         {
            /* There is no need to do the conversions to and from linear space,
             * so the calculation should be a lot more accurate.  There is a
-             * built in 1/32768 error in the coefficients because they only have
-             * 15 bits and are adjusted to make sure they add up to 32768, so
-             * the result may have an additional error up to 1/32768.  (Note
-             * that adding the 1/32768 here avoids needing to increase the
-             * global error limits to take this into account.)
+             * built in error in the coefficients because they only have 15 bits
+             * and are adjusted to make sure they add up to 32768.  This
+             * involves a integer calculation with truncation of the form:
+             *
+             *     ((int)(coefficient * 100000) * 32768)/100000
+             *
+             * This is done to the red and green coefficients (the ones
+             * provided to the API) then blue is calculated from them so the
+             * result adds up to 32768.  In the worst case this can result in
+             * a -1 error in red and green and a +2 error in blue.  Consequently
+             * the worst case in the calculation below is 2/32768 error.
+             *
+             * TODO: consider fixing this in libpng by rounding the calculation
+             * limiting the error to 1/32768.
+             *
+             * Handling this by adding 2/32768 here avoids needing to increase
+             * the global error limits to take this into account.)
             */
            gray = r * data.red_coefficient + g * data.green_coefficient +
               b * data.blue_coefficient;
            err = re * data.red_coefficient + ge * data.green_coefficient +
-               be * data.blue_coefficient + 1./32768 + gray * 5 * DBL_EPSILON;
+               be * data.blue_coefficient + 2./32768 + gray * 5 * DBL_EPSILON;
         }

         else
@@ -7304,7 +7450,7 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
             * previously added input quantization error at this point.
             */
            gray = r * data.red_coefficient + g * data.green_coefficient +
-               b * data.blue_coefficient - 1./32768 - out_qe;
+               b * data.blue_coefficient - 2./32768 - out_qe;
            if (gray <= 0)
               gray = 0;
            else
@@ -7314,7 +7460,7 @@ image_transform_png_set_rgb_to_gray_mod(PNG_CONST image_transform *this,
            }

            grayhi = rhi * data.red_coefficient + ghi * data.green_coefficient +
-               bhi * data.blue_coefficient + 1./32768 + out_qe;
+               bhi * data.blue_coefficient + 2./32768 + out_qe;
            grayhi *= (1 + 6 * DBL_EPSILON);
            if (grayhi >= 1)
               grayhi = 1;
@@ -7429,6 +7575,9 @@ image_transform_png_set_background_set(PNG_CONST image_transform *this,

   else
   {
+      if (that->this.has_tRNS)
+         that->this.is_transparent = 1;
+
      bit_depth = that->this.bit_depth;
      expand = 1;
   }
@@ -7506,14 +7655,14 @@ image_transform_png_set_background_mod(PNG_CONST image_transform *this,
      /* Remove the alpha type and set the alpha (not in that order.) */
      that->alphaf = 1;
      that->alphae = 0;
-
-      if (that->colour_type == PNG_COLOR_TYPE_RGB_ALPHA)
-         that->colour_type = PNG_COLOR_TYPE_RGB;
-      else if (that->colour_type == PNG_COLOR_TYPE_GRAY_ALPHA)
-         that->colour_type = PNG_COLOR_TYPE_GRAY;
-      /* PNG_COLOR_TYPE_PALETTE is not changed */
   }

+   if (that->colour_type == PNG_COLOR_TYPE_RGB_ALPHA)
+      that->colour_type = PNG_COLOR_TYPE_RGB;
+   else if (that->colour_type == PNG_COLOR_TYPE_GRAY_ALPHA)
+      that->colour_type = PNG_COLOR_TYPE_GRAY;
+   /* PNG_COLOR_TYPE_PALETTE is not changed */
+
   this->next->mod(this->next, that, pp, display);
 }

@@ -8301,7 +8450,8 @@ perform_transform_test(png_modifier *pm)
   png_byte bit_depth = 0;
   unsigned int palette_number = 0;

-   while (next_format(&colour_type, &bit_depth, &palette_number, 0))
+   while (next_format(&colour_type, &bit_depth, &palette_number, pm->test_lbg,
+            pm->test_tRNS))
   {
      png_uint_32 counter = 0;
      size_t base_pos;
@@ -8604,7 +8754,9 @@ init_validate_info(validate_info *vi, gamma_display *dp, png_const_structp pp,
   vi->outlog = outlog(dp->pm, in_depth, out_depth);

   if ((dp->this.colour_type & PNG_COLOR_MASK_ALPHA) != 0 ||
-      (dp->this.colour_type == 3 && dp->this.is_transparent))
+      (dp->this.colour_type == 3 && dp->this.is_transparent) ||
+      ((dp->this.colour_type == 0 || dp->this.colour_type == 2) &&
+       dp->this.has_tRNS))
   {
      vi->do_background = dp->do_background;

@@ -8634,7 +8786,7 @@ init_validate_info(validate_info *vi, gamma_display *dp, png_const_structp pp,
         vi->background_blue = b;
      }
   }
-   else
+   else /* Do not expect any background processing */
      vi->do_background = 0;

   if (vi->do_background == 0)
@@ -9350,6 +9502,7 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
   png_uint_32 y;
   PNG_CONST store_palette_entry *in_palette = dp->this.palette;
   PNG_CONST int in_is_transparent = dp->this.is_transparent;
+   int process_tRNS;
   int out_npalette = -1;
   int out_is_transparent = 0; /* Just refers to the palette case */
   store_palette out_palette;
@@ -9365,6 +9518,7 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,

   processing = (vi.gamma_correction > 0 && !dp->threshold_test)
      || in_bd != out_bd || in_ct != out_ct || vi.do_background;
+   process_tRNS = dp->this.has_tRNS && vi.do_background;

   /* TODO: FIX THIS: MAJOR BUG!  If the transformations all happen inside
    * the palette there is no way of finding out, because libpng fails to
@@ -9403,8 +9557,8 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
            /* Handle input alpha - png_set_background will cause the output
             * alpha to disappear so there is nothing to check.
             */
-            if ((in_ct & PNG_COLOR_MASK_ALPHA) != 0 || (in_ct == 3 &&
-               in_is_transparent))
+            if ((in_ct & PNG_COLOR_MASK_ALPHA) != 0 ||
+                (in_ct == 3 && in_is_transparent))
            {
               PNG_CONST unsigned int input_alpha = in_ct == 3 ?
                  dp->this.palette[in_index].alpha :
@@ -9436,6 +9590,35 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
               }
            }

+            else if (process_tRNS)
+            {
+               /* alpha needs to be set appropriately for this pixel, it is
+                * currently 1 and needs to be 0 for an input pixel which matches
+                * the values in tRNS.
+                */
+               switch (in_ct)
+               {
+                  case 0: /* gray */
+                     if (sample(std, in_ct, in_bd, x, 0, 0, 0) ==
+                           dp->this.transparent.red)
+                        alpha = 0;
+                     break;
+
+                  case 2: /* RGB */
+                     if (sample(std, in_ct, in_bd, x, 0, 0, 0) ==
+                           dp->this.transparent.red &&
+                         sample(std, in_ct, in_bd, x, 1, 0, 0) ==
+                           dp->this.transparent.green &&
+                         sample(std, in_ct, in_bd, x, 2, 0, 0) ==
+                           dp->this.transparent.blue)
+                        alpha = 0;
+                     break;
+
+                  default:
+                     break;
+               }
+            }
+
            /* Handle grayscale or RGB components. */
            if ((in_ct & PNG_COLOR_MASK_COLOR) == 0) /* grayscale */
               (void)gamma_component_validate("gray", &vi,
@@ -9545,7 +9728,7 @@ gamma_test(png_modifier *pmIn, PNG_CONST png_byte colour_typeIn,

      modification_reset(d.pm->modifications);

-      /* Get a png_struct for writing the image. */
+      /* Get a png_struct for reading the image. */
      pp = set_modifier_for_read(d.pm, &pi, d.this.id, name);
      standard_palette_init(&d.this);

@@ -9684,9 +9867,13 @@ perform_gamma_threshold_tests(png_modifier *pm)
   /* Don't test more than one instance of each palette - it's pointless, in
    * fact this test is somewhat excessive since libpng doesn't make this
    * decision based on colour type or bit depth!
+    *
+    * CHANGED: now test two palettes and, as a side effect, images with and
+    * without tRNS.
    */
-   while (next_format(&colour_type, &bit_depth, &palette_number, 1/*gamma*/))
-      if (palette_number == 0)
+   while (next_format(&colour_type, &bit_depth, &palette_number,
+                      pm->test_lbg_gamma_threshold, pm->test_tRNS))
+      if (palette_number < 2)
   {
      double test_gamma = 1.0;
      while (test_gamma >= .4)
@@ -9746,7 +9933,8 @@ static void perform_gamma_transform_tests(png_modifier *pm)
   png_byte bit_depth = 0;
   unsigned int palette_number = 0;

-   while (next_format(&colour_type, &bit_depth, &palette_number, 1/*gamma*/))
+   while (next_format(&colour_type, &bit_depth, &palette_number,
+                      pm->test_lbg_gamma_transform, pm->test_tRNS))
   {
      unsigned int i, j;

@@ -9776,7 +9964,8 @@ static void perform_gamma_sbit_tests(png_modifier *pm)
      png_byte colour_type = 0, bit_depth = 0;
      unsigned int npalette = 0;

-      while (next_format(&colour_type, &bit_depth, &npalette, 1/*gamma*/))
+      while (next_format(&colour_type, &bit_depth, &npalette,
+                         pm->test_lbg_gamma_sbit, pm->test_tRNS))
         if ((colour_type & PNG_COLOR_MASK_ALPHA) == 0 &&
            ((colour_type == 3 && sbit < 8) ||
            (colour_type != 3 && sbit < bit_depth)))
@@ -9967,8 +10156,17 @@ static void gamma_composition_test(png_modifier *pm,
   }

   background.index = 193; /* rgb(193,193,193) to detect errors */
+
   if (!(colour_type & PNG_COLOR_MASK_COLOR))
   {
+      /* Because, currently, png_set_background is always called with
+       * 'need_expand' false in this case and because the gamma test itself
+       * doesn't cause an expand to 8-bit for lower bit depths the colour must
+       * be reduced to the correct range.
+       */
+      if (bit_depth < 8)
+         background.gray &= (png_uint_16)((1U << bit_depth)-1);
+
      /* Grayscale input, we do not convert to RGB (TBD), so we must set the
       * background to gray - else libpng seems to fail.
       */
@@ -10017,9 +10215,18 @@ perform_gamma_composition_tests(png_modifier *pm, int do_background,

   /* Skip the non-alpha cases - there is no setting of a transparency colour at
    * present.
+    *
+    * TODO: incorrect; the palette case sets tRNS and, now RGB and gray do,
+    * however the palette case fails miserably so is commented out below.
    */
-   while (next_format(&colour_type, &bit_depth, &palette_number, 1/*gamma*/))
-      if ((colour_type & PNG_COLOR_MASK_ALPHA) != 0)
+   while (next_format(&colour_type, &bit_depth, &palette_number,
+                      pm->test_lbg_gamma_composition, pm->test_tRNS))
+      if ((colour_type & PNG_COLOR_MASK_ALPHA) != 0
+#if 0 /* TODO: FIXME */
+          /*TODO: FIXME: this should work */
+          || colour_type == 3
+#endif
+          || (colour_type != 3 && palette_number != 0))
   {
      unsigned int i, j;

@@ -10751,6 +10958,18 @@ int main(int argc, char **argv)
   pm.ngammas = ARRAY_SIZE(gammas);
   pm.ngamma_tests = 0; /* default to off */

+   /* Low bit depth gray images don't do well in the gamma tests, until
+    * this is fixed turn them off for some gamma cases:
+    */
+#  ifdef PNG_WRITE_tRNS_SUPPORTED
+      pm.test_tRNS = 1;
+#  endif
+   pm.test_lbg = 0;
+   pm.test_lbg_gamma_threshold = 1;
+   pm.test_lbg_gamma_transform = 0/*PNG_LIBPNG_VER >= 10700*/;
+   pm.test_lbg_gamma_sbit = 1;
+   pm.test_lbg_gamma_composition = 0;
+
   /* And the test encodings */
   pm.encodings = test_encodings;
   pm.nencodings = ARRAY_SIZE(test_encodings);
@@ -10863,7 +11082,7 @@ int main(int argc, char **argv)
         pm.test_gamma_transform = 1;
         pm.test_gamma_sbit = 1;
         pm.test_gamma_scale16 = 1;
-         pm.test_gamma_background = 1;
+         pm.test_gamma_background = 1; /* composition */
         pm.test_gamma_alpha_mode = 1;
         }

@@ -10912,6 +11131,24 @@ int main(int argc, char **argv)
      else if (strcmp(*argv, "--noexpand16") == 0)
         pm.test_gamma_expand16 = 0;

+      else if (strcmp(*argv, "--low-depth-gray") == 0)
+         pm.test_lbg = pm.test_lbg_gamma_threshold =
+            pm.test_lbg_gamma_transform = pm.test_lbg_gamma_sbit =
+            pm.test_lbg_gamma_composition = 1;
+
+      else if (strcmp(*argv, "--nolow-depth-gray") == 0)
+         pm.test_lbg = pm.test_lbg_gamma_threshold =
+            pm.test_lbg_gamma_transform = pm.test_lbg_gamma_sbit =
+            pm.test_lbg_gamma_composition = 0;
+
+#     ifdef PNG_WRITE_tRNS_SUPPORTED
+         else if (strcmp(*argv, "--tRNS") == 0)
+            pm.test_tRNS = 1;
+#     endif
+
+      else if (strcmp(*argv, "--notRNS") == 0)
+         pm.test_tRNS = 0;
+
      else if (strcmp(*argv, "--more-gammas") == 0)
         pm.ngamma_tests = 3U;

@@ -11102,7 +11339,7 @@ int main(int argc, char **argv)
   Try
   {
      /* Make useful base images */
-      make_transform_images(&pm.this);
+      make_transform_images(&pm);

      /* Perform the standard and gamma tests. */
      if (pm.test_standard)
--- a/contrib/tools/pngfix.c
+++ b/contrib/tools/pngfix.c
@@ -2138,7 +2138,7 @@ zlib_end(struct zlib *zlib)
          *
          * z-rc is the zlib failure code; message is the error message with
          * spaces replaced by '-'.  The compressed byte count indicates where
-          * in the zlib stream the error occured.
+          * in the zlib stream the error occurred.
          */
         type_name(zlib->chunk->chunk_type, stdout);
         printf(" SKP %s %d %s ", zlib_flevel(zlib), zlib->file_bits,
@@ -3702,21 +3702,21 @@ usage(const char *prog)
 "        gAMA, sRGB [all]: These specify the gamma encoding used for the pixel",
 "            values.",
 "        cHRM, iCCP [color]: These specify how colors are encoded.  iCCP also",
-"            specifies the exact encoding of a pixel value however in practice",
-"            most programs will ignore it.",
+"            specifies the exact encoding of a pixel value; however, in",
+"            practice most programs will ignore it.",
 "        bKGD [transform]: This is used by libpng transforms."
 "    --max=<number>:",
 "      Use IDAT chunks sized <number>.  If no number is given the the IDAT",
 "      chunks will be the maximum size permitted; 2^31-1 bytes.  If the option",
 "      is omitted the original chunk sizes will not be changed.  When the",
-"      option is given --strip=unsafe is set automatically, this may be",
+"      option is given --strip=unsafe is set automatically. This may be",
 "      cancelled if you know that all unknown unsafe-to-copy chunks really are",
 "      safe to copy across an IDAT size change.  This is true of all chunks",
 "      that have ever been formally proposed as PNG extensions.",
 "  MESSAGES",
 "      By default the program only outputs summaries for each file.",
 "    --quiet (-q):",
-"      Do not output the summaries except for files which cannot be read. With",
+"      Do not output the summaries except for files that cannot be read. With",
 "      two --quiets these are not output either.",
 "    --errors (-e):",
 "      Output errors from libpng and the program (except too-far-back).",
@@ -3749,7 +3749,7 @@ usage(const char *prog)
 "  the following codes.  Notice that the results for each file are combined",
 "  together - check one file at a time to get a meaningful error code!",
 "    0x01: The zlib too-far-back error existed in at least one chunk.",
-"    0x02: At least once chunk had a CRC error.",
+"    0x02: At least one chunk had a CRC error.",
 "    0x04: A chunk length was incorrect.",
 "    0x08: The file was truncated.",
 "  Errors less than 16 are potentially recoverable, for a single file if the",
@@ -3757,7 +3757,7 @@ usage(const char *prog)
 "  non-zero code is returned).",
 "    0x10: The file could not be read, even with corrections.",
 "    0x20: The output file could not be written.",
-"    0x40: An unexpected, potentially internal, error occured.",
+"    0x40: An unexpected, potentially internal, error occurred.",
 "  If the command line arguments are incorrect the program exits with exit",
 "  255.  Some older operating systems only support 7-bit exit codes, on those",
 "  systems it is suggested that this program is first tested by supplying",
@@ -3817,7 +3817,7 @@ usage(const char *prog)
 "          SKP: The chunk was skipped because of a zlib issue (zlib-rc) with",
 "               explanation 'message'",
 "          ERR: The read of the file was aborted.  The parameters explain why.",
-"$3 status:     For 'ERR' the accumulate status code from 'EXIT CODES' above.",
+"$3 status:     For 'ERR' the accumulated status code from 'EXIT CODES' above.",
 "               This is printed as a 2 digit hexadecimal value",
 "   comp-level: The recorded compression level (FLEVEL) of a zlib stream",
 "               expressed as a string {supfast,stdfast,default,maximum}",
--- 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 1.6.17beta05 - February 23, 2015
+ libpng version 1.6.18beta02 - April 26, 2015
 Updated and distributed by Glenn Randers-Pehrson
 <glennrp at users.sourceforge.net>
 Copyright (c) 1998-2015 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 1.6.17beta05 - February 23, 2015
+ libpng versions 0.97, January 1998, through 1.6.18beta02 - April 26, 2015
 Updated and distributed by Glenn Randers-Pehrson
 Copyright (c) 1998-2015 Glenn Randers-Pehrson

@@ -336,7 +336,7 @@ prediction.

 If you are intending to keep the file pointer open for use in libpng,
 you must ensure you don't read more than 8 bytes from the beginning
-of the file, and you also have to make a call to png_set_sig_bytes_read()
+of the file, and you also have to make a call to png_set_sig_bytes()
 with the number of bytes you read from the beginning.  Libpng will
 then only check the bytes (if any) that your program didn't read.

@@ -1994,7 +1994,7 @@ value when you call it in this position:
      png_set_gamma(png_ptr, screen_gamma, 0.45455);

 If you need to reduce an RGB file to a paletted file, or if a paletted
-file has more entries then will fit on your screen, png_set_quantize()
+file has more entries than will fit on your screen, png_set_quantize()
 will do that.  Note that this is a simple match quantization that merely
 finds the closest color available.  This should work fairly well with
 optimized palettes, but fairly badly with linear color cubes.  If you
@@ -2547,7 +2547,7 @@ png_infop info_ptr;
       64K.  The library seems to run fine with sizes
       of 4K. Although you can give it much less if
       necessary (I assume you can give it chunks of
-       1 byte, I haven't tried less then 256 bytes
+       1 byte, I haven't tried less than 256 bytes
       yet).  When this function returns, you may
       want to display any rows that were generated
       in the row callback if you don't already do
@@ -5032,6 +5032,10 @@ The signatures of many exported functions were changed, such that
   png_infop became png_inforp or png_const_inforp
 where "rp" indicates a "restricted pointer".

+The support for FAR/far types has been eliminated and the definition of
+png_alloc_size_t is now controlled by a flag so that 'small size_t' systems
+can select it if necessary.
+
 Error detection in some chunks has improved; in particular the iCCP chunk
 reader now does pretty complete validation of the basic format.  Some bad
 profiles that were previously accepted are now accepted with a warning or
@@ -5275,13 +5279,13 @@ Other rules can be inferred by inspecting the libpng source.

 XVI. Y2K Compliance in libpng

-February 23, 2015
+April 26, 2015

 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 1.6.17beta05 are Y2K compliant.  It is my belief that earlier
+upward through 1.6.18beta02 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
--- a/libpng.3
+++ b/libpng.3
@@ -1,6 +1,6 @@
-.TH LIBPNG 3 "February 23, 2015"
+.TH LIBPNG 3 "April 26, 2015"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.6.17beta05
+libpng \- Portable Network Graphics (PNG) Reference Library 1.6.18beta02
 .SH SYNOPSIS
 \fB
 #include <png.h>\fP
@@ -504,7 +504,7 @@ 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 1.6.17beta05 - February 23, 2015
+ libpng version 1.6.18beta02 - April 26, 2015
 Updated and distributed by Glenn Randers-Pehrson
 <glennrp at users.sourceforge.net>
 Copyright (c) 1998-2015 Glenn Randers-Pehrson
@@ -515,7 +515,7 @@ libpng-manual.txt - A description on how to use and modify libpng

 Based on:

- libpng versions 0.97, January 1998, through 1.6.17beta05 - February 23, 2015
+ libpng versions 0.97, January 1998, through 1.6.18beta02 - April 26, 2015
 Updated and distributed by Glenn Randers-Pehrson
 Copyright (c) 1998-2015 Glenn Randers-Pehrson

@@ -840,7 +840,7 @@ prediction.

 If you are intending to keep the file pointer open for use in libpng,
 you must ensure you don't read more than 8 bytes from the beginning
-of the file, and you also have to make a call to png_set_sig_bytes_read()
+of the file, and you also have to make a call to png_set_sig_bytes()
 with the number of bytes you read from the beginning.  Libpng will
 then only check the bytes (if any) that your program didn't read.

@@ -2498,7 +2498,7 @@ value when you call it in this position:
      png_set_gamma(png_ptr, screen_gamma, 0.45455);

 If you need to reduce an RGB file to a paletted file, or if a paletted
-file has more entries then will fit on your screen, png_set_quantize()
+file has more entries than will fit on your screen, png_set_quantize()
 will do that.  Note that this is a simple match quantization that merely
 finds the closest color available.  This should work fairly well with
 optimized palettes, but fairly badly with linear color cubes.  If you
@@ -3051,7 +3051,7 @@ png_infop info_ptr;
       64K.  The library seems to run fine with sizes
       of 4K. Although you can give it much less if
       necessary (I assume you can give it chunks of
-       1 byte, I haven't tried less then 256 bytes
+       1 byte, I haven't tried less than 256 bytes
       yet).  When this function returns, you may
       want to display any rows that were generated
       in the row callback if you don't already do
@@ -5536,6 +5536,10 @@ The signatures of many exported functions were changed, such that
   png_infop became png_inforp or png_const_inforp
 where "rp" indicates a "restricted pointer".

+The support for FAR/far types has been eliminated and the definition of
+png_alloc_size_t is now controlled by a flag so that 'small size_t' systems
+can select it if necessary.
+
 Error detection in some chunks has improved; in particular the iCCP chunk
 reader now does pretty complete validation of the basic format.  Some bad
 profiles that were previously accepted are now accepted with a warning or
@@ -5779,13 +5783,13 @@ Other rules can be inferred by inspecting the libpng source.

 .SH XVI. Y2K Compliance in libpng

-February 23, 2015
+April 26, 2015

 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 1.6.17beta05 are Y2K compliant.  It is my belief that earlier
+upward through 1.6.18beta02 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
@@ -6037,7 +6041,10 @@ the first widely used release:
 1.6.16beta01-03     16    10616  16.so.16.16[.0]
 1.6.16rc01-02       16    10616  16.so.16.16[.0]
 1.6.16              16    10616  16.so.16.16[.0]
- 1.6.17beta01-05     16    10617  16.so.16.17[.0]
+ 1.6.17beta01-06     16    10617  16.so.16.17[.0]
+ 1.6.17rc01-06       16    10617  16.so.16.17[.0]
+ 1.6.17              16    10617  16.so.16.17[.0]
+ 1.6.18beta01-02     16    10618  16.so.16.18[.0]

 Henceforth the source version will match the shared-library minor
 and patch numbers; the shared-library major version number will be
@@ -6094,7 +6101,7 @@ possible without all of you.

 Thanks to Frank J. T. Wojcik for helping with the documentation.

-Libpng version 1.6.17beta05 - February 23, 2015:
+Libpng version 1.6.18beta02 - April 26, 2015:
 Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
 Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).

@@ -6117,8 +6124,8 @@ this sentence.

 This code is released under the libpng license.

-libpng versions 1.2.6, August 15, 2004, through 1.6.17beta05, February 23, 2015, are
-Copyright (c) 2004,2006-2014 Glenn Randers-Pehrson, and are
+libpng versions 1.2.6, August 15, 2004, through 1.6.18beta02, April 26, 2015, are
+Copyright (c) 2004,2006-2015 Glenn Randers-Pehrson, and are
 distributed according to the same disclaimer and license as libpng-1.2.5
 with the following individual added to the list of Contributing Authors

@@ -6216,7 +6223,7 @@ certification mark of the Open Source Initiative.

 Glenn Randers-Pehrson
 glennrp at users.sourceforge.net
-February 23, 2015
+April 26, 2015

 .\" end of man page

--- a/libpngpf.3
+++ b/libpngpf.3
@@ -1,6 +1,6 @@
-.TH LIBPNGPF 3 "February 23, 2015"
+.TH LIBPNGPF 3 "April 26, 2015"
 .SH NAME
-libpng \- Portable Network Graphics (PNG) Reference Library 1.6.17beta05
+libpng \- Portable Network Graphics (PNG) Reference Library 1.6.18beta02
 (private functions)
 .SH SYNOPSIS
 \fB#include \fI"pngpriv.h"
--- a/png.5
+++ b/png.5
@@ -1,4 +1,4 @@
-.TH PNG 5 "February 23, 2015"
+.TH PNG 5 "April 26, 2015"
 .SH NAME
 png \- Portable Network Graphics (PNG) format
 .SH DESCRIPTION
--- a/png.c
+++ b/png.c
@@ -1,7 +1,7 @@

 /* png.c - location for general purpose libpng functions
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 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 +14,7 @@
 #include "pngpriv.h"

 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_6_17beta05 Your_png_h_is_not_version_1_6_17beta05;
+typedef png_libpng_version_1_6_18beta02 Your_png_h_is_not_version_1_6_18beta02;

 /* 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
@@ -34,7 +34,7 @@ png_set_sig_bytes(png_structrp png_ptr, int num_bytes)
   if (num_bytes > 8)
      png_error(png_ptr, "Too many bytes for PNG signature");

-   png_ptr->sig_bytes = (png_byte)(num_bytes < 0 ? 0 : num_bytes);
+   png_ptr->sig_bytes = (png_byte)((num_bytes < 0 ? 0 : num_bytes) & 0xff);
 }

 /* Checks whether the supplied bytes match the PNG signature.  We allow
@@ -547,20 +547,17 @@ png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask,

      else
      {
-         if (info_ptr->splt_palettes_num != 0)
+         int i;
+
+         for (i = 0; i < info_ptr->splt_palettes_num; i++)
         {
-            int i;
-
-            for (i = 0; i < info_ptr->splt_palettes_num; i++)
-            {
-               png_free(png_ptr, info_ptr->splt_palettes[i].name);
-               png_free(png_ptr, info_ptr->splt_palettes[i].entries);
-            }
-
-            png_free(png_ptr, info_ptr->splt_palettes);
-            info_ptr->splt_palettes = NULL;
-            info_ptr->splt_palettes_num = 0;
+            png_free(png_ptr, info_ptr->splt_palettes[i].name);
+            png_free(png_ptr, info_ptr->splt_palettes[i].entries);
         }
+
+         png_free(png_ptr, info_ptr->splt_palettes);
+         info_ptr->splt_palettes = NULL;
+         info_ptr->splt_palettes_num = 0;
         info_ptr->valid &= ~PNG_INFO_sPLT;
      }
   }
@@ -580,15 +577,12 @@ png_free_data(png_const_structrp png_ptr, png_inforp info_ptr, png_uint_32 mask,
      {
         int i;

-         if (info_ptr->unknown_chunks_num != 0)
-         {
-            for (i = 0; i < info_ptr->unknown_chunks_num; i++)
-               png_free(png_ptr, info_ptr->unknown_chunks[i].data);
+         for (i = 0; i < info_ptr->unknown_chunks_num; i++)
+            png_free(png_ptr, info_ptr->unknown_chunks[i].data);

-            png_free(png_ptr, info_ptr->unknown_chunks);
-            info_ptr->unknown_chunks = NULL;
-            info_ptr->unknown_chunks_num = 0;
-         }
+         png_free(png_ptr, info_ptr->unknown_chunks);
+         info_ptr->unknown_chunks = NULL;
+         info_ptr->unknown_chunks_num = 0;
      }
   }
 #endif
@@ -772,13 +766,13 @@ png_get_copyright(png_const_structrp png_ptr)
 #else
 #  ifdef __STDC__
   return PNG_STRING_NEWLINE \
-     "libpng version 1.6.17beta05 - February 23, 2015" PNG_STRING_NEWLINE \
+     "libpng version 1.6.18beta02 - April 26, 2015" PNG_STRING_NEWLINE \
     "Copyright (c) 1998-2015 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 1.6.17beta05 - February 23, 2015\
+      return "libpng version 1.6.18beta02 - April 26, 2015\
      Copyright (c) 1998-2015 Glenn Randers-Pehrson\
      Copyright (c) 1996-1997 Andreas Dilger\
      Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.";
@@ -875,9 +869,9 @@ png_build_grayscale_palette(int bit_depth, png_colorp palette)

   for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
   {
-      palette[i].red = (png_byte)v;
-      palette[i].green = (png_byte)v;
-      palette[i].blue = (png_byte)v;
+      palette[i].red = (png_byte)(v & 0xff);
+      palette[i].green = (png_byte)(v & 0xff);
+      palette[i].blue = (png_byte)(v & 0xff);
   }
 }
 #endif
@@ -2282,7 +2276,7 @@ png_compare_ICC_profile_with_sRGB(png_const_structrp png_ptr,

         /* Length *and* intent must match */
         if (length == png_sRGB_checks[i].length &&
-            intent == png_sRGB_checks[i].intent)
+            intent == (png_uint_32) png_sRGB_checks[i].intent)
         {
            /* Now calculate the adler32 if not done already. */
            if (adler == 0)
@@ -3040,7 +3034,7 @@ 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
-             * to '-1' because of the decrement after outputing
+             * to '-1' because of the decrement after outputting
             * the decimal point above (the exponent required is
             * *not* -1!)
             */
@@ -3048,7 +3042,7 @@ png_ascii_from_fp(png_const_structrp png_ptr, png_charp ascii, png_size_t size,
            {
               /* The following only happens if we didn't output the
                * leading zeros above for negative exponent, so this
-                * doest add to the digit requirement.  Note that the
+                * doesn't add to the digit requirement.  Note that the
                * two zeros here can only be output if the two leading
                * zeros were *not* output, so this doesn't increase
                * the output count.
@@ -3733,7 +3727,7 @@ png_exp8bit(png_fixed_point lg2)
    * step.
    */
   x -= x >> 8;
-   return (png_byte)((x + 0x7fffffU) >> 24);
+   return (png_byte)(((x + 0x7fffffU) >> 24) & 0xff);
 }

 #ifdef PNG_16BIT_SUPPORTED
@@ -3794,7 +3788,7 @@ png_gamma_8bit_correct(unsigned int value, png_fixed_point gamma_val)
 #     endif
   }

-   return (png_byte)value;
+   return (png_byte)(value & 0xff);
 }

 #ifdef PNG_16BIT_SUPPORTED
@@ -4016,7 +4010,7 @@ png_build_8bit_table(png_structrp png_ptr, png_bytepp ptable,

   else
      for (i=0; i<256; ++i)
-         table[i] = (png_byte)i;
+         table[i] = (png_byte)(i & 0xff);
 }

 /* Used from png_read_destroy and below to release the memory used by the gamma
@@ -4156,7 +4150,8 @@ png_build_gamma_table(png_structrp png_ptr, int bit_depth)
      *
      */
     if (sig_bit > 0 && sig_bit < 16U)
-        shift = (png_byte)(16U - sig_bit); /* shift == insignificant bits */
+        /* shift == insignificant bits */
+        shift = (png_byte)((16U - sig_bit) & 0xff);

     else
        shift = 0; /* keep all 16 bits */
@@ -4225,7 +4220,7 @@ png_set_option(png_structrp png_ptr, int option, int onoff)
      int setting = (2 + (onoff != 0)) << option;
      int current = png_ptr->options;

-      png_ptr->options = (png_byte)((current & ~mask) | setting);
+      png_ptr->options = (png_byte)(((current & ~mask) | setting) & 0xff);

      return (current & mask) >> option;
   }
--- a/png.h
+++ b/png.h
@@ -1,7 +1,8 @@

 /* png.h - header file for PNG reference library
 *
- * libpng version 1.6.17beta05, February 23, 2015
+ * libpng version 1.6.18beta02, April 26, 2015
+ *
 * Copyright (c) 1998-2015 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.)
@@ -11,7 +12,7 @@
 * Authors and maintainers:
 *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
 *   libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.6.17beta05, February 23, 2015: Glenn
+ *   libpng versions 0.97, January 1998, through 1.6.18beta02, April 26, 2015: Glenn
 *   See also "Contributing Authors", below.
 *
 * Note about libpng version numbers:
@@ -212,7 +213,10 @@
 *    1.6.16beta01-03         16    10616  16.so.16.16[.0]
 *    1.6.16rc01-02           16    10616  16.so.16.16[.0]
 *    1.6.16                  16    10616  16.so.16.16[.0]
- *    1.6.17beta01-05         16    10617  16.so.16.17[.0]
+ *    1.6.17beta01-06         16    10617  16.so.16.17[.0]
+ *    1.6.17rc01-06           16    10617  16.so.16.17[.0]
+ *    1.6.17                  16    10617  16.so.16.17[.0]
+ *    1.6.18beta01-02         16    10618  16.so.16.18[.0]
 *
 *   Henceforth the source version will match the shared-library major
 *   and minor numbers; the shared-library major version number will be
@@ -244,7 +248,7 @@
 *
 * This code is released under the libpng license.
 *
- * libpng versions 1.2.6, August 15, 2004, through 1.6.17beta05, February 23, 2015, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.6.18beta02, April 26, 2015, are
 * Copyright (c) 2004, 2006-2015 Glenn Randers-Pehrson, and are
 * distributed according to the same disclaimer and license as libpng-1.2.5
 * with the following individual added to the list of Contributing Authors:
@@ -356,13 +360,13 @@
 * Y2K compliance in libpng:
 * =========================
 *
- *    February 23, 2015
+ *    April 26, 2015
 *
 *    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 1.6.17beta05 are Y2K compliant.  It is my belief that
+ *    upward through 1.6.18beta02 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
@@ -424,9 +428,9 @@
 */

 /* Version information for png.h - this should match the version in png.c */
-#define PNG_LIBPNG_VER_STRING "1.6.17beta05"
+#define PNG_LIBPNG_VER_STRING "1.6.18beta02"
 #define PNG_HEADER_VERSION_STRING \
-     " libpng version 1.6.17beta05 - February 23, 2015\n"
+     " libpng version 1.6.18beta02 - April 26, 2015\n"

 #define PNG_LIBPNG_VER_SONUM   16
 #define PNG_LIBPNG_VER_DLLNUM  16
@@ -434,13 +438,13 @@
 /* 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 17
+#define PNG_LIBPNG_VER_RELEASE 18

 /* This should match the numeric part of the final component of
 * PNG_LIBPNG_VER_STRING, omitting any leading zero:
 */

-#define PNG_LIBPNG_VER_BUILD  05
+#define PNG_LIBPNG_VER_BUILD  02

 /* Release Status */
 #define PNG_LIBPNG_BUILD_ALPHA    1
@@ -465,7 +469,7 @@
 * 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 10617 /* 1.6.17 */
+#define PNG_LIBPNG_VER 10618 /* 1.6.18 */

 /* Library configuration: these options cannot be changed after
 * the library has been built.
@@ -570,7 +574,7 @@ 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_17beta05;
+typedef char* png_libpng_version_1_6_18beta02;

 /* Basic control structions.  Read libpng-manual.txt or libpng.3 for more info.
 *
@@ -1579,6 +1583,7 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
 #define PNG_CRC_QUIET_USE     4  /* quiet/use data      quiet/use data    */
 #define PNG_CRC_NO_CHANGE     5  /* use current value   use current value */

+#ifdef PNG_WRITE_SUPPORTED
 /* These functions give the user control over the scan-line filtering in
 * libpng and the compression methods used by zlib.  These functions are
 * mainly useful for testing, as the defaults should work with most users.
@@ -1592,6 +1597,7 @@ PNG_EXPORT(66, void, png_set_crc_action, (png_structrp png_ptr, int crit_action,
 */
 PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
    int filters));
+#endif /* WRITE */

 /* Flags for png_set_filter() to say which filters to use.  The flags
 * are chosen so that they don't conflict with real filter types
@@ -1617,6 +1623,7 @@ PNG_EXPORT(67, void, png_set_filter, (png_structrp png_ptr, int method,
 #define PNG_FILTER_VALUE_PAETH 4
 #define PNG_FILTER_VALUE_LAST  5

+#ifdef PNG_WRITE_SUPPORTED
 #ifdef PNG_WRITE_WEIGHTED_FILTER_SUPPORTED /* EXPERIMENTAL */
 /* The "heuristic_method" is given by one of the PNG_FILTER_HEURISTIC_
 * defines, either the default (minimum-sum-of-absolute-differences), or
@@ -1663,7 +1670,6 @@ PNG_FIXED_EXPORT(209, void, png_set_filter_heuristics_fixed,
 #define PNG_FILTER_HEURISTIC_WEIGHTED   2  /* Experimental feature */
 #define PNG_FILTER_HEURISTIC_LAST       3  /* Not a valid value */

-#ifdef PNG_WRITE_SUPPORTED
 /* Set the library compression level.  Currently, valid values range from
 * 0 - 9, corresponding directly to the zlib compression levels 0 - 9
 * (0 - no compression, 9 - "maximal" compression).  Note that tests have
@@ -1822,7 +1828,7 @@ PNG_EXPORT(218, png_byte, png_get_current_pass_number, (png_const_structrp));
 *
 * The integer return from the callback function is interpreted thus:
 *
- * negative: An error occured, png_chunk_error will be called.
+ * negative: An error occurred; png_chunk_error will be called.
 *     zero: The chunk was not handled, the chunk will be saved. A critical
 *           chunk will cause an error at this point unless it is to be saved.
 * positive: The chunk was handled, libpng will ignore/discard it.
@@ -2667,26 +2673,28 @@ PNG_EXPORT(216, png_uint_32, png_get_io_chunk_type,
           * (png_uint_16)(alpha)                         \
           + (png_uint_16)(bg)*(png_uint_16)(255          \
           - (png_uint_16)(alpha)) + 128);                \
-       (composite) = (png_byte)((temp + (temp >> 8)) >> 8); }
+       (composite) = (png_byte)(((temp + (temp >> 8)) >> 8) & 0xff); }

 #  define png_composite_16(composite, fg, alpha, bg)       \
     { png_uint_32 temp = (png_uint_32)((png_uint_32)(fg)  \
           * (png_uint_32)(alpha)                          \
           + (png_uint_32)(bg)*(65535                      \
           - (png_uint_32)(alpha)) + 32768);               \
-       (composite) = (png_uint_16)((temp + (temp >> 16)) >> 16); }
+       (composite) = (png_uint_16)(0xffff & ((temp + (temp >> 16)) >> 16)); }

 #else  /* Standard method using integer division */

-#  define png_composite(composite, fg, alpha, bg)                          \
-     (composite) = (png_byte)(((png_uint_16)(fg) * (png_uint_16)(alpha) +  \
-     (png_uint_16)(bg) * (png_uint_16)(255 - (png_uint_16)(alpha)) +       \
-     127) / 255)
+#  define png_composite(composite, fg, alpha, bg)                        \
+     (composite) =                                                       \
+         (png_byte)(0xff & (((png_uint_16)(fg) * (png_uint_16)(alpha) +  \
+         (png_uint_16)(bg) * (png_uint_16)(255 - (png_uint_16)(alpha)) + \
+         127) / 255))

 #  define png_composite_16(composite, fg, alpha, bg)                         \
-     (composite) = (png_uint_16)(((png_uint_32)(fg) * (png_uint_32)(alpha) + \
-     (png_uint_32)(bg)*(png_uint_32)(65535 - (png_uint_32)(alpha)) +         \
-     32767) / 65535)
+     (composite) =                                                           \
+         (png_uint_16)(0xffff & (((png_uint_32)(fg) * (png_uint_32)(alpha) + \
+         (png_uint_32)(bg)*(png_uint_32)(65535 - (png_uint_32)(alpha)) +     \
+         32767) / 65535))
 #endif /* READ_COMPOSITE_NODIV */

 #ifdef PNG_READ_INT_FUNCTIONS_SUPPORTED
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@

 /* pngconf.h - machine configurable file for libpng
 *
- * libpng version 1.6.17beta05, (PENDING RELEASE)
+ * libpng version 1.6.18beta02, (PENDING RELEASE)
 *
 * Copyright (c) 1998-2015 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
@@ -11,9 +11,7 @@
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
- */
-
-/* Any machine specific code is near the front of this file, so if you
+ * Any machine specific code is near the front of this file, so if you
 * are configuring libpng for a machine, you may want to read the section
 * starting here down to where it starts to typedef png_color, png_text,
 * and png_info.
--- a/pngget.c
+++ b/pngget.c
@@ -1,7 +1,7 @@

 /* pngget.c - retrieval of values from info struct
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
--- a/pngmem.c
+++ b/pngmem.c
@@ -41,7 +41,7 @@ png_destroy_png_struct(png_structrp png_ptr)
 }

 /* Allocate memory.  For reasonable files, size should never exceed
- * 64K.  However, zlib may allocate more then 64K if you don't tell
+ * 64K.  However, zlib may allocate more than 64K if you don't tell
 * it not to.  See zconf.h and png.h for more information.  zlib does
 * need to allocate exactly 64K, so whatever you call here must
 * have the ability to do that.
@@ -77,6 +77,9 @@ png_malloc_base,(png_const_structrp png_ptr, png_alloc_size_t size),
   PNG_UNUSED(png_ptr)
 #endif

+   /* Some compilers complain that this is always true.  However, it
+    * can be false when integer overflow happens.
+    */
   if (size > 0 && size <= PNG_SIZE_MAX
 #     ifdef PNG_MAX_MALLOC_64K
         && size <= 65536U
--- a/pngpread.c
+++ b/pngpread.c
@@ -1,7 +1,7 @@

 /* pngpread.c - read a png file in push mode
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 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.)
@@ -584,13 +584,11 @@ png_push_save_buffer(png_structrp png_ptr)
      if (png_ptr->save_buffer == NULL)
      {
         png_free(png_ptr, old_buffer);
-         old_buffer = NULL;
         png_error(png_ptr, "Insufficient memory for save_buffer");
      }

      memcpy(png_ptr->save_buffer, old_buffer, png_ptr->save_buffer_size);
      png_free(png_ptr, old_buffer);
-      old_buffer = NULL;
      png_ptr->save_buffer_max = new_max;
   }
   if (png_ptr->current_buffer_size)
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1,7 +1,7 @@

 /* pngpriv.h - private declarations for use inside libpng
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
@@ -741,15 +741,17 @@
 * macro will fail on top-bit-set values because of the sign extension.
 */
 #define PNG_CHUNK_FROM_STRING(s)\
-   PNG_U32(0xff&(s)[0], 0xff&(s)[1], 0xff&(s)[2], 0xff&(s)[3])
+   PNG_U32(0xff & (s)[0], 0xff & (s)[1], 0xff & (s)[2], 0xff & (s)[3])

 /* This uses (char), not (png_byte) to avoid warnings on systems where (char) is
 * signed and the argument is a (char[])  This macro will fail miserably on
 * systems where (char) is more than 8 bits.
 */
 #define PNG_STRING_FROM_CHUNK(s,c)\
-   (void)(((char*)(s))[0]=(char)((c)>>24), ((char*)(s))[1]=(char)((c)>>16),\
-   ((char*)(s))[2]=(char)((c)>>8), ((char*)(s))[3]=(char)((c)))
+   (void)(((char*)(s))[0]=(char)(((c)>>24) & 0xff), \
+   ((char*)(s))[1]=(char)(((c)>>16) & 0xff),\
+   ((char*)(s))[2]=(char)(((c)>>8) & 0xff), \
+   ((char*)(s))[3]=(char)((c & 0xff)))

 /* Do the same but terminate with a null character. */
 #define PNG_CSTRING_FROM_CHUNK(s,c)\
@@ -811,8 +813,9 @@ PNG_INTERNAL_DATA(const png_uint_16, png_sRGB_table, [256]);
 PNG_INTERNAL_DATA(const png_uint_16, png_sRGB_base, [512]);
 PNG_INTERNAL_DATA(const png_byte, png_sRGB_delta, [512]);

-#define PNG_sRGB_FROM_LINEAR(linear) ((png_byte)((png_sRGB_base[(linear)>>15] +\
-   ((((linear)&0x7fff)*png_sRGB_delta[(linear)>>15])>>12)) >> 8))
+#define PNG_sRGB_FROM_LINEAR(linear) \
+  ((png_byte)(0xff & ((png_sRGB_base[(linear)>>15] \
+   + ((((linear) & 0x7fff)*png_sRGB_delta[(linear)>>15])>>12)) >> 8)))
   /* Given a value 'linear' in the range 0..255*65535 calculate the 8-bit sRGB
    * encoded value with maximum error 0.646365.  Note that the input is not a
    * 16-bit value; it has been multiplied by 255! */
--- a/pngread.c
+++ b/pngread.c
@@ -1,7 +1,7 @@

 /* pngread.c - read a PNG file
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
@@ -1823,6 +1823,7 @@ png_create_colormap_entry(png_image_read_control *display,
            y = (y + 128) >> 8;
            y *= 255;
            y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
+            alpha = PNG_DIV257(alpha);
            encoding = P_sRGB;
         }

--- a/pngrio.c
+++ b/pngrio.c
@@ -1,7 +1,7 @@

 /* pngrio.c - functions for data input
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
@@ -26,7 +26,7 @@
 * reads from a file pointer.  Note that this routine sometimes gets called
 * with very small lengths, so you should implement some kind of simple
 * buffering if you are using unbuffered reads.  This should never be asked
- * to read more then 64K on a 16 bit machine.
+ * to read more than 64K on a 16 bit machine.
 */
 void /* PRIVATE */
 png_read_data(png_structrp png_ptr, png_bytep data, png_size_t length)
--- 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 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 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.)
@@ -394,7 +394,7 @@ png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
 /* Dither file to 8-bit.  Supply a palette, the current number
 * of elements in the palette, the maximum number of elements
 * allowed, and a histogram if possible.  If the current number
- * of colors is greater then the maximum number, the palette will be
+ * of colors is greater than the maximum number, the palette will be
 * modified to fit in the maximum number.  "full_quantize" indicates
 * whether we need a quantizing cube set up for RGB images, or if we
 * simply are reducing the number of colors in a paletted image.
@@ -2357,7 +2357,7 @@ png_do_unshift(png_row_infop row_info, png_bytep row,
               if (++channel >= channels)
                  channel = 0;
               *bp++ = (png_byte)(value >> 8);
-               *bp++ = (png_byte)(value & 0xff);
+               *bp++ = (png_byte)value;
            }
            break;
         }
@@ -2662,9 +2662,9 @@ png_do_read_filler(png_row_infop row_info, png_bytep row,
   png_uint_32 row_width = row_info->width;

 #ifdef PNG_READ_16BIT_SUPPORTED
-   png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
+   png_byte hi_filler = (png_byte)(filler>>8);
 #endif
-   png_byte lo_filler = (png_byte)(filler & 0xff);
+   png_byte lo_filler = (png_byte)filler;

   png_debug(1, "in png_do_read_filler");

@@ -3105,16 +3105,16 @@ png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)

               else
               {
-                  png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
+                  png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red & 0xff)
                      >> png_ptr->gamma_shift][red>>8];
                  png_uint_16 green_1 =
-                      png_ptr->gamma_16_to_1[(green&0xff) >>
+                      png_ptr->gamma_16_to_1[(green & 0xff) >>
                      png_ptr->gamma_shift][green>>8];
-                  png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
+                  png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue & 0xff)
                      >> png_ptr->gamma_shift][blue>>8];
                  png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
                      + bc*blue_1 + 16384)>>15);
-                  w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
+                  w = png_ptr->gamma_16_from_1[(gray16 & 0xff) >>
                      png_ptr->gamma_shift][gray16 >> 8];
                  rgb_error |= 1;
               }
@@ -3669,7 +3669,8 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
                        if (optimize != 0)
                           w = v;
                        else
-                           w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
+                           w = gamma_16_from_1[(v & 0xff) >>
+                               gamma_shift][v >> 8];
                        *sp = (png_byte)((w >> 8) & 0xff);
                        *(sp + 1) = (png_byte)(w & 0xff);
                     }
@@ -3833,7 +3834,7 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
                        v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                        png_composite_16(w, v, a, png_ptr->background_1.red);
                        if (optimize == 0)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
+                           w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
                                8];
                        *sp = (png_byte)((w >> 8) & 0xff);
                        *(sp + 1) = (png_byte)(w & 0xff);
@@ -3841,7 +3842,7 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
                        v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
                        png_composite_16(w, v, a, png_ptr->background_1.green);
                        if (optimize == 0)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
+                           w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
                                8];

                        *(sp + 2) = (png_byte)((w >> 8) & 0xff);
@@ -3850,7 +3851,7 @@ png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
                        v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
                        png_composite_16(w, v, a, png_ptr->background_1.blue);
                        if (optimize == 0)
-                           w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
+                           w = gamma_16_from_1[((w & 0xff) >> gamma_shift)][w >>
                                8];

                        *(sp + 4) = (png_byte)((w >> 8) & 0xff);
@@ -4459,7 +4460,7 @@ png_do_expand(png_row_infop row_info, png_bytep row,

               for (i = 0; i < row_width; i++)
               {
-                  if (*sp == gray)
+                  if ((*sp & 0xff) == gray)
                     *dp-- = 0;

                  else
@@ -4477,7 +4478,8 @@ png_do_expand(png_row_infop row_info, png_bytep row,
               dp = row + (row_info->rowbytes << 1) - 1;
               for (i = 0; i < row_width; i++)
               {
-                  if (*(sp - 1) == gray_high && *(sp) == gray_low)
+                  if ((*(sp - 1) & 0xff) == gray_high &&
+                      (*(sp) & 0xff) == gray_low)
                  {
                     *dp-- = 0;
                     *dp-- = 0;
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1,7 +1,7 @@

 /* pngrutil.c - utilities to read a PNG file
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 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.)
@@ -575,7 +575,7 @@ png_decompress_chunk(png_structrp png_ptr,
    */
   png_alloc_size_t limit = PNG_SIZE_MAX;

-# ifdef PNG_SET_CHUNK_MALLOC_LIMIT_SUPPORTED
+# ifdef PNG_SET_USER_LIMITS_SUPPORTED
   if (png_ptr->user_chunk_malloc_max > 0 &&
       png_ptr->user_chunk_malloc_max < limit)
      limit = png_ptr->user_chunk_malloc_max;
@@ -670,7 +670,6 @@ png_decompress_chunk(png_structrp png_ptr,
                   * success)
                   */
                  png_free(png_ptr, text);
-                  text = NULL;

                  /* This really is very benign, but it's still an error because
                   * the extra space may otherwise be used as a Trojan Horse.
@@ -1817,7 +1816,8 @@ png_handle_tRNS(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
         return;
      }

-      if (length > png_ptr->num_palette || length > PNG_MAX_PALETTE_LENGTH ||
+      if (length > png_ptr->num_palette ||
+         length > (unsigned int) PNG_MAX_PALETTE_LENGTH ||
         length == 0)
      {
         png_crc_finish(png_ptr, length);
@@ -1980,7 +1980,7 @@ png_handle_hIST(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)

   num = length / 2 ;

-   if (num != png_ptr->num_palette || num > PNG_MAX_PALETTE_LENGTH)
+   if (num != png_ptr->num_palette || num > (unsigned int) PNG_MAX_PALETTE_LENGTH)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "invalid");
@@ -2715,7 +2715,7 @@ png_cache_unknown_chunk(png_structrp png_ptr, png_uint_32 length)
      png_ptr->unknown_chunk.data = NULL;
   }

-#  ifdef PNG_SET_CHUNK_MALLOC_LIMIT_SUPPORTED
+#  ifdef PNG_SET_USER_LIMITS_SUPPORTED
      if (png_ptr->user_chunk_malloc_max > 0 &&
          png_ptr->user_chunk_malloc_max < limit)
         limit = png_ptr->user_chunk_malloc_max;
@@ -2806,7 +2806,7 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
               &png_ptr->unknown_chunk);

            /* ret is:
-             * negative: An error occured, png_chunk_error will be called.
+             * negative: An error occurred; png_chunk_error will be called.
             *     zero: The chunk was not handled, the chunk will be discarded
             *           unless png_set_keep_unknown_chunks has been used to set
             *           a 'keep' behavior for this particular chunk, in which
@@ -4446,11 +4446,8 @@ defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
   png_debug1(3, "height = %u,", png_ptr->height);
   png_debug1(3, "iwidth = %u,", png_ptr->iwidth);
   png_debug1(3, "num_rows = %u,", png_ptr->num_rows);
-   png_debug1(3, "row_bytes = %lu,", (unsigned long)row_bytes);
-   png_debug1(3, "png_ptr->rowbytes = %lu,", (unsigned long)png_ptr->rowbytes);
-   png_debug1(3, "png_ptr->info_rowbytes = %lu,",
-       (unsigned long)png_ptr->info_rowbytes);
-   png_debug1(3, "PNG_ROWBYTES = %lu",
+   png_debug1(3, "rowbytes = %lu,", (unsigned long)png_ptr->rowbytes);
+   png_debug1(3, "irowbytes = %lu",
       (unsigned long)PNG_ROWBYTES(png_ptr->pixel_depth, png_ptr->iwidth) + 1);

   /* The sequential reader needs a buffer for IDAT, but the progressive reader
--- a/pngset.c
+++ b/pngset.c
@@ -1,7 +1,7 @@

 /* pngset.c - storage of image information into info struct
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
 * Copyright (c) 1998-2015 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.)
@@ -673,7 +673,6 @@ png_set_iCCP(png_const_structrp png_ptr, png_inforp info_ptr,
   if (new_iccp_profile == NULL)
   {
      png_free(png_ptr, new_iccp_name);
-      new_iccp_name = NULL;
      png_benign_error(png_ptr,
          "Insufficient memory to process iCCP profile");

@@ -1254,8 +1253,7 @@ png_set_unknown_chunk_location(png_const_structrp png_ptr, png_inforp info_ptr,
         check_location(png_ptr, location);
   }
 }
-#endif
-
+#endif /* STORE_UNKNOWN_CHUNKS */

 #ifdef PNG_MNG_FEATURES_SUPPORTED
 png_uint_32 PNGAPI
@@ -1523,6 +1521,9 @@ png_set_compression_buffer_size(png_structrp png_ptr, png_size_t size)
         }

 #ifndef __COVERITY__
+         /* Some compilers complain that this is always false.  However, it
+          * can be true when integer overflow happens.
+          */
         if (size > ZLIB_IO_MAX)
         {
            png_warning(png_ptr,
--- a/pngtest.c
+++ b/pngtest.c
@@ -1,7 +1,7 @@

 /* pngtest.c - a simple test program to test libpng
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
@@ -469,7 +469,7 @@ pngtest_error(png_structp png_ptr, png_const_charp message)
 #if defined(PNG_USER_MEM_SUPPORTED) && PNG_DEBUG

 /* Allocate memory.  For reasonable files, size should never exceed
- * 64K.  However, zlib may allocate more then 64K if you don't tell
+ * 64K.  However, zlib may allocate more than 64K if you don't tell
 * it not to.  See zconf.h and png.h for more information.  zlib does
 * need to allocate exactly 64K, so whatever you call here must
 * have the ability to do that.
@@ -2028,4 +2028,4 @@ main(void)
 #endif

 /* Generate a compiler error if there is an old png.h in the search path. */
-typedef png_libpng_version_1_6_17beta05 Your_png_h_is_not_version_1_6_17beta05;
+typedef png_libpng_version_1_6_18beta02 Your_png_h_is_not_version_1_6_18beta02;
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -1,8 +1,8 @@

 /* pngtrans.c - transforms the data in a row (used by both readers and writers)
 *
- * Last changed in libpng 1.6.15 [November 20, 2014]
- * Copyright (c) 1998-2014 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
+ * Copyright (c) 1998-2015 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.)
 *
@@ -704,7 +704,7 @@ png_do_check_palette_indexes(png_structrp png_ptr, png_row_infop row_info)
             */
            for (; rp > png_ptr->row_buf; rp--)
            {
-              if (*rp >> padding != 0)
+              if ((*rp >> padding) != 0)
                 png_ptr->num_palette_max = 1;
              padding = 0;
            }
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -1,8 +1,8 @@

 /* pngwrite.c - general routines to write a PNG file
 *
- * Last changed in libpng 1.6.15 [November 20, 2014]
- * Copyright (c) 1998-2014 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.17 [March 26, 2015]
+ * Copyright (c) 1998-2015 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.)
 *
@@ -638,8 +638,8 @@ png_do_write_intrapixel(png_row_infop row_info, png_bytep row)

         for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
         {
-            *(rp)     = (png_byte)((*rp       - *(rp + 1)) & 0xff);
-            *(rp + 2) = (png_byte)((*(rp + 2) - *(rp + 1)) & 0xff);
+            *(rp)     = (png_byte)(*rp       - *(rp + 1));
+            *(rp + 2) = (png_byte)(*(rp + 2) - *(rp + 1));
         }
      }

@@ -665,10 +665,10 @@ png_do_write_intrapixel(png_row_infop row_info, png_bytep row)
            png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
            png_uint_32 red  = (png_uint_32)((s0 - s1) & 0xffffL);
            png_uint_32 blue = (png_uint_32)((s2 - s1) & 0xffffL);
-            *(rp    ) = (png_byte)((red >> 8) & 0xff);
-            *(rp + 1) = (png_byte)(red & 0xff);
-            *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
-            *(rp + 5) = (png_byte)(blue & 0xff);
+            *(rp    ) = (png_byte)(red >> 8);
+            *(rp + 1) = (png_byte)red;
+            *(rp + 4) = (png_byte)(blue >> 8);
+            *(rp + 5) = (png_byte)blue;
         }
      }
 #endif /* WRITE_16BIT */
@@ -1050,8 +1050,8 @@ png_set_filter(png_structrp png_ptr, int method, int filters)
       * it is too late to start using the filters that need it, since we
       * will be missing the data in the previous row.  If an application
       * wants to start and stop using particular filters during compression,
-       * it should start out with all of the filters, and then add and
-       * remove them after the start of compression.
+       * it should start out with all of the filters, and then remove them
+       * or add them back after the start of compression.
       */
      if (png_ptr->row_buf != NULL)
      {
@@ -1418,8 +1418,8 @@ png_set_compression_window_bits(png_structrp png_ptr, int window_bits)
   if (png_ptr == NULL)
      return;

-   /* Prior to 1.6.0 this would warn but then set the window_bits value, this
-    * meant that negative window bits values could be selected which would cause
+   /* Prior to 1.6.0 this would warn but then set the window_bits value. This
+    * meant that negative window bits values could be selected that would cause
    * libpng to write a non-standard PNG file with raw deflate or gzip
    * compressed IDAT or ancillary chunks.  Such files can be read and there is
    * no warning on read, so this seems like a very bad idea.
--- a/pngwtran.c
+++ b/pngwtran.c
@@ -1,8 +1,8 @@

 /* pngwtran.c - transforms the data in a row for PNG writers
 *
- * Last changed in libpng 1.6.15 [November 20, 2014]
- * Copyright (c) 1998-2014 Glenn Randers-Pehrson
+ * Last changed in libpng 1.6.18 [(PENDING RELEASE)]
+ * Copyright (c) 1998-2015 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.)
 *
@@ -422,7 +422,7 @@ png_do_write_invert_alpha(png_row_infop row_info, png_bytep row)
               *(dp++) = *(sp++);
               */
               sp+=3; dp = sp;
-               *(dp++) = (png_byte)(255 - *(sp++));
+               *dp = (png_byte)(255 - *(sp++));
            }
         }

@@ -446,7 +446,7 @@ png_do_write_invert_alpha(png_row_infop row_info, png_bytep row)
               */
               sp+=6; dp = sp;
               *(dp++) = (png_byte)(255 - *(sp++));
-               *(dp++) = (png_byte)(255 - *(sp++));
+               *dp     = (png_byte)(255 - *(sp++));
            }
         }
 #endif /* WRITE_16BIT */
@@ -484,7 +484,7 @@ png_do_write_invert_alpha(png_row_infop row_info, png_bytep row)
               */
               sp+=2; dp = sp;
               *(dp++) = (png_byte)(255 - *(sp++));
-               *(dp++) = (png_byte)(255 - *(sp++));
+               *dp     = (png_byte)(255 - *(sp++));
            }
         }
 #endif /* WRITE_16BIT */
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -1,7 +1,7 @@

 /* pngwutil.c - utilities to write a PNG file
 *
- * Last changed in libpng 1.6.17 [(PENDING RELEASE)]
+ * Last changed in libpng 1.6.17 [March 26, 2015]
 * Copyright (c) 1998-2015 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.)
@@ -23,10 +23,10 @@
 void PNGAPI
 png_save_uint_32(png_bytep buf, png_uint_32 i)
 {
-   buf[0] = (png_byte)((i >> 24) & 0xff);
-   buf[1] = (png_byte)((i >> 16) & 0xff);
-   buf[2] = (png_byte)((i >> 8) & 0xff);
-   buf[3] = (png_byte)(i & 0xff);
+   buf[0] = (png_byte)(i >> 24);
+   buf[1] = (png_byte)(i >> 16);
+   buf[2] = (png_byte)(i >> 8);
+   buf[3] = (png_byte)(i     );
 }

 /* Place a 16-bit number into a buffer in PNG byte order.
@@ -36,8 +36,8 @@ png_save_uint_32(png_bytep buf, png_uint_32 i)
 void PNGAPI
 png_save_uint_16(png_bytep buf, unsigned int i)
 {
-   buf[0] = (png_byte)((i >> 8) & 0xff);
-   buf[1] = (png_byte)(i & 0xff);
+   buf[0] = (png_byte)(i >> 8);
+   buf[1] = (png_byte)(i     );
 }
 #endif

@@ -695,7 +695,7 @@ png_check_keyword(png_structrp png_ptr, png_const_charp key, png_bytep new_key)

   while (*key && key_len < 79)
   {
-      png_byte ch = (png_byte)(0xff & *key++);
+      png_byte ch = (png_byte)*key++;

      if ((ch > 32 && ch <= 126) || (ch >= 161 /*&& ch <= 255*/))
         *new_key++ = ch, ++key_len, space = 0;
@@ -871,7 +871,7 @@ png_write_IHDR(png_structrp png_ptr, png_uint_32 width, png_uint_32 height,
   interlace_type=PNG_INTERLACE_NONE;
 #endif

-   /* Save the relevent information */
+   /* Save the relevant information */
   png_ptr->bit_depth = (png_byte)bit_depth;
   png_ptr->color_type = (png_byte)color_type;
   png_ptr->interlaced = (png_byte)interlace_type;
@@ -2453,7 +2453,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (lp = row_buf + 1; i < row_bytes;
         i++, rp++, lp++, dp++)
      {
-         *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
+         *dp = (png_byte)((int)*rp - (int)*lp);
      }

      best_row = png_ptr->sub_row;
@@ -2515,7 +2515,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (lp = row_buf + 1; i < row_bytes;
         i++, rp++, lp++, dp++)
      {
-         v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
+         v = *dp = (png_byte)((int)*rp - (int)*lp);

         sum += (v < 128) ? v : 256 - v;

@@ -2574,7 +2574,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
          pp = prev_row + 1; i < row_bytes;
          i++, rp++, pp++, dp++)
      {
-         *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
+         *dp = (png_byte)((int)*rp - (int)*pp);
      }

      best_row = png_ptr->up_row;
@@ -2625,7 +2625,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (i = 0, rp = row_buf + 1, dp = png_ptr->up_row + 1,
          pp = prev_row + 1; i < row_bytes; i++)
      {
-         v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
+         v = *dp++ = (png_byte)((int)*rp++ - (int)*pp++);

         sum += (v < 128) ? v : 256 - v;

@@ -2683,13 +2683,13 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
           pp = prev_row + 1; i < bpp; i++)
      {
-         *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
+         *dp++ = (png_byte)((int)*rp++ - ((int)*pp++ / 2));
      }

      for (lp = row_buf + 1; i < row_bytes; i++)
      {
-         *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
-                 & 0xff);
+         *dp++ =
+             (png_byte)((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2));
      }
      best_row = png_ptr->avg_row;
   }
@@ -2738,7 +2738,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (i = 0, rp = row_buf + 1, dp = png_ptr->avg_row + 1,
           pp = prev_row + 1; i < bpp; i++)
      {
-         v = *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
+         v = *dp++ = (png_byte)((int)*rp++ - ((int)*pp++ / 2));

         sum += (v < 128) ? v : 256 - v;
      }
@@ -2746,7 +2746,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (lp = row_buf + 1; i < row_bytes; i++)
      {
         v = *dp++ =
-             (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2)) & 0xff);
+             (png_byte)(((int)*rp++ - ((int)*pp++ + (int)*lp++) / 2));

         sum += (v < 128) ? v : 256 - v;

@@ -2804,7 +2804,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
          pp = prev_row + 1; i < bpp; i++)
      {
-         *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
+         *dp++ = (png_byte)((int)*rp++ - (int)*pp++);
      }

      for (lp = row_buf + 1, cp = prev_row + 1; i < row_bytes; i++)
@@ -2830,7 +2830,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)

         p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;

-         *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
+         *dp++ = (png_byte)((int)*rp++ - p);
      }
      best_row = png_ptr->paeth_row;
   }
@@ -2879,7 +2879,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
      for (i = 0, rp = row_buf + 1, dp = png_ptr->paeth_row + 1,
          pp = prev_row + 1; i < bpp; i++)
      {
-         v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
+         v = *dp++ = (png_byte)((int)*rp++ - (int)*pp++);

         sum += (v < 128) ? v : 256 - v;
      }
@@ -2921,7 +2921,7 @@ png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
            p = c;
 #endif /* SLOW_PAETH */

-         v = *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
+         v = *dp++ = (png_byte)((int)*rp++ - p);

         sum += (v < 128) ? v : 256 - v;

--- a/projects/vstudio/readme.txt
+++ b/projects/vstudio/readme.txt
@@ -1,7 +1,7 @@

 VisualStudio instructions

-libpng version 1.6.17beta05 - February 23, 2015
+libpng version 1.6.18beta02 - April 26, 2015

 Copyright (c) 1998-2010 Glenn Randers-Pehrson

--- a/projects/vstudio/zlib.props
+++ b/projects/vstudio/zlib.props
@@ -2,7 +2,7 @@
 <!--
 * zlib.props - location of zlib source
 *
- * libpng version 1.6.17beta05 - February 23, 2015
+ * libpng version 1.6.18beta02 - April 26, 2015
 *
 * Copyright (c) 1998-2011 Glenn Randers-Pehrson
 *
--- a/scripts/README.txt
+++ b/scripts/README.txt
@@ -1,9 +1,9 @@

-Makefiles for  libpng version 1.6.17beta05 - February 23, 2015
+Makefiles for  libpng version 1.6.18beta02 - April 26, 2015

 pnglibconf.h.prebuilt       =>  Stores configuration settings
 makefile.linux    =>  Linux/ELF makefile
-                       (gcc, creates libpng16.so.16.1.6.17beta05)
+                       (gcc, creates libpng16.so.16.1.6.18beta02)
 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 +33,12 @@ 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.16.1.6.17beta05)
+                       creates libpng16.so.16.1.6.18beta02)
 makefile.sgi      =>  Silicon Graphics IRIX makefile (cc, creates static lib)
 makefile.solaris  =>  Solaris 2.X makefile (gcc,
-                       creates libpng16.so.16.1.6.17beta05)
+                       creates libpng16.so.16.1.6.18beta02)
 makefile.so9      =>  Solaris 9 makefile (gcc,
-                       creates libpng16.so.16.1.6.17beta05)
+                       creates libpng16.so.16.1.6.18beta02)
 makefile.std      =>  Generic UNIX makefile (cc, creates static libpng.a)
 makefile.sunos    =>  Sun makefile
 makefile.32sunu   =>  Sun Ultra 32-bit makefile
--- 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 1.6.17beta05"
+PNG_DFN ";Version 1.6.18beta02"

 #define PNG_EXPORTA(ordinal, type, name, args, attributes)\
        PNG_DFN "@" SYMBOL_PREFIX "@@" name "@"
--- a/scripts/dfn.awk
+++ b/scripts/dfn.awk
@@ -17,7 +17,7 @@
 BEGIN{
   out="/dev/null"       # as a flag
   out_count=0           # count of output lines
-   err=0                 # set if an error occured
+   err=0                 # set if an error occurred
   sort=0                # sort the output
   array[""]=""
 }
--- a/scripts/libpng-config-head.in
+++ b/scripts/libpng-config-head.in
@@ -11,7 +11,7 @@

 # Modeled after libxml-config.

-version=1.6.17beta05
+version=1.6.18beta02
 prefix=""
 libdir=""
 libs=""
--- 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: 1.6.17beta05
+Version: 1.6.18beta02
 Libs: -L${libdir} -lpng16
 Cflags: -I${includedir}
--- a/scripts/makefile.cegcc
+++ b/scripts/makefile.cegcc
@@ -23,7 +23,7 @@

 VERMAJ = 1
 VERMIN = 6
-VERMIC = 17
+VERMIC = 18
 VER = $(VERMAJ).$(VERMIN).$(VERMIC)
 NAME = libpng
 PACKAGE = $(NAME)-$(VER)
--- a/scripts/makefile.linux
+++ b/scripts/makefile.linux
@@ -10,7 +10,7 @@
 # Library name:
 LIBNAME = libpng16
 PNGMAJ = 16
-RELEASE = 17
+RELEASE = 18

 # Shared library names:
 LIBSO=$(LIBNAME).so
--- a/scripts/makefile.msys
+++ b/scripts/makefile.msys
@@ -18,7 +18,7 @@ exec_prefix=$(prefix)
 # Library name:
 LIBNAME = libpng16
 PNGMAJ = 16
-RELEASE = 17
+RELEASE = 18

 # Shared library names:
 LIBSO=$(LIBNAME).dll
--- a/scripts/makefile.ne12bsd
+++ b/scripts/makefile.ne12bsd
@@ -17,7 +17,7 @@ INCSDIR=${LOCALBASE}/include/libpng16

 LIB=	png16
 SHLIB_MAJOR=	0
-SHLIB_MINOR=	1.6.17beta05
+SHLIB_MINOR=	1.6.18beta02
 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
--- a/scripts/makefile.netbsd
+++ b/scripts/makefile.netbsd
@@ -17,7 +17,7 @@ INCSDIR=${LOCALBASE}/include

 LIB=	png
 SHLIB_MAJOR=	16
-SHLIB_MINOR=	1.6.17beta05
+SHLIB_MINOR=	1.6.18beta02
 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
--- a/scripts/makefile.openbsd
+++ b/scripts/makefile.openbsd
@@ -11,7 +11,7 @@ LIBDIR=	${PREFIX}/lib
 MANDIR= ${PREFIX}/man/cat

 SHLIB_MAJOR=	16
-SHLIB_MINOR=	1.6.17beta05
+SHLIB_MINOR=	1.6.18beta02

 LIB=	png
 SRCS=	png.c pngerror.c pngget.c pngmem.c pngpread.c \
--- a/scripts/makefile.std
+++ b/scripts/makefile.std
@@ -106,7 +106,8 @@ install: libpng.a pnglibconf.h
 	chmod 644 $(DESTDIR)$(LIBPATH)/libpng.a

 clean:
-	$(RM_F) *.o libpng.a pngtest pngout.png pnglibconf.*
+	$(RM_F) *.o libpng.a pngtest pngout.png pnglibconf.h pnglibconf.c \
+	pnglibconf.out

 DOCS = ANNOUNCE CHANGES INSTALL KNOWNBUG LICENSE README TODO Y2KINFO
 writelock:
--- a/scripts/pnglibconf.dfa
+++ b/scripts/pnglibconf.dfa
@@ -367,11 +367,14 @@ option USER_LIMITS requires READ
 # USER_CHUNK_CACHE_MAX: maximum number of chunks to be cached
 #
 # Only chunks that are variable in number are counted towards the
-# USER_CHUNK_CACHE_MAX limit
-setting USER_WIDTH_MAX default        1000000 /* Use 0x7fffffff for unlimited */
-setting USER_HEIGHT_MAX default       1000000 /* Use 0x7fffffff for unlimited */
-setting USER_CHUNK_CACHE_MAX default     1000 /* Use 0 for unlimited */
-setting USER_CHUNK_MALLOC_MAX default 8000000 /* Use 0 for unlimited */
+
+# Use 0x7fffffff for unlimited
+setting USER_WIDTH_MAX default        1000000
+setting USER_HEIGHT_MAX default       1000000
+
+# Use 0 for unlimited
+setting USER_CHUNK_CACHE_MAX default     1000
+setting USER_CHUNK_MALLOC_MAX default 8000000

 # If this option is enabled APIs to set the above limits at run time are added;
 # without this the hardwired (compile time) limits will be used.
@@ -643,7 +646,7 @@ setting QUANTIZE_BLUE_BITS default 5
 # are only interested in 8 bits anyway.  Increasing this value
 # results in more memory being used, and more pow() functions
 # being called to fill in the gamma tables.  Don't set this value
-# less then 8, and even that may not work (I haven't tested it).
+# less than 8, and even that may not work (I haven't tested it).

 setting MAX_GAMMA_8 default 11

--- a/scripts/pnglibconf.h.prebuilt
+++ b/scripts/pnglibconf.h.prebuilt
@@ -1,8 +1,8 @@
-/* libpng 1.6.17beta05 STANDARD API DEFINITION */
+/* libpng 1.6.18beta02 STANDARD API DEFINITION */

 /* pnglibconf.h - library build configuration */

-/* Libpng version 1.6.17beta05 - February 23, 2015 */
+/* Libpng version 1.6.18beta02 - April 26, 2015 */

 /* Copyright (c) 1998-2014 Glenn Randers-Pehrson */

@@ -101,8 +101,6 @@
 #define PNG_SAVE_UNKNOWN_CHUNKS_SUPPORTED
 #define PNG_SEQUENTIAL_READ_SUPPORTED
 #define PNG_SETJMP_SUPPORTED
-#define PNG_SET_CHUNK_CACHE_LIMIT_SUPPORTED
-#define PNG_SET_CHUNK_MALLOC_LIMIT_SUPPORTED
 #define PNG_SET_OPTION_SUPPORTED
 #define PNG_SET_UNKNOWN_CHUNKS_SUPPORTED
 #define PNG_SET_USER_LIMITS_SUPPORTED
@@ -198,10 +196,10 @@
 #define PNG_QUANTIZE_RED_BITS 5
 #define PNG_TEXT_Z_DEFAULT_COMPRESSION (-1)
 #define PNG_TEXT_Z_DEFAULT_STRATEGY 0
-#define PNG_USER_CHUNK_CACHE_MAX 1000 /* Use 0 for unlimited */
-#define PNG_USER_CHUNK_MALLOC_MAX 8000000 /* Use 0 for unlimited */
-#define PNG_USER_HEIGHT_MAX 1000000 /* Use 0x7fffffff for unlimited */
-#define PNG_USER_WIDTH_MAX 1000000 /* Use 0x7fffffff for unlimited */
+#define PNG_USER_CHUNK_CACHE_MAX 1000
+#define PNG_USER_CHUNK_MALLOC_MAX 8000000
+#define PNG_USER_HEIGHT_MAX 1000000
+#define PNG_USER_WIDTH_MAX 1000000
 #define PNG_WEIGHT_SHIFT 8
 #define PNG_ZBUF_SIZE 8192
 #define PNG_ZLIB_VERNUM 0 /* unknown */
--- a/scripts/pnglibconf.mak
+++ b/scripts/pnglibconf.mak
@@ -49,6 +49,7 @@ pnglibconf.dfn: $(srcdir)/scripts/pnglibconf.dfa $(srcdir)/scripts/options.awk $
 	$(MOVE) pnglibconf.tmp $@

 clean-pnglibconf:
-	$(DELETE) pnglibconf.*
+	$(DELETE) pnglibconf.h pnglibconf.c pnglibconf.out pnglibconf.pre \
+	pnglibconf.dfn

 clean: clean-pnglibconf
--- a/scripts/symbols.def
+++ b/scripts/symbols.def
@@ -1,4 +1,4 @@
-;Version 1.6.17beta05
+;Version 1.6.18beta02
 ;--------------------------------------------------------------
 ; LIBPNG symbol list as a Win32 DEF file
 ; Contains all the symbols that can be exported from libpng
Author	SHA1	Message	Date
Glenn Randers-Pehrson	ecc391bbcf	[libpng16] Imported from libpng-1.6.18beta02.tar	2015-04-26 16:38:10 -05:00
Glenn Randers-Pehrson	c861dc8923	[libpng16] Suppressed some warnings from the Borland C++ 5.5.1/5.82 compiler (Bug report by Viktor Szaka'ts).	2015-04-01 12:06:01 -05:00
Glenn Randers-Pehrson	507a8cdc5e	[libpng16] Bump version to 1.6.18beta02	2015-04-01 08:24:26 -05:00
Glenn Randers-Pehrson	bd85b5713c	[libpng16] Imported from libpng-1.6.18beta01.tar	2015-04-01 08:24:14 -05:00
John Bowler	a21a5b22c1	[libpng16] Fixed rgb_to_gray checks and added tRNS checks to pngvalid.c	2015-03-30 21:38:31 -05:00
Glenn Randers-Pehrson	d344589703	[libpng16] Removed PNG_SET_CHUNK_[CACHE\|MALLOC]_LIMIT_SUPPORTED macros. They have been combined with PNG_SET_USER_LIMITS_SUPPORTED (resolves bug report by Andrew Church).	2015-03-27 08:58:32 -05:00
Glenn Randers-Pehrson	218a6fe9e5	[libpng16] Bump version to 1.6.18beta01	2015-03-26 08:55:25 -05:00
Glenn Randers-Pehrson	c98f7fb4e3	[libpng16] Imported from libpng-1.6.17.tar	2015-03-26 08:11:12 -05:00
Glenn Randers-Pehrson	f17e6c3046	[libpng16] Imported from libpng-1.6.17rc06.tar	2015-03-22 19:43:23 -05:00
John Bowler	6eecfe3886	[libpng16] Fixed simplified 8-bit-linear to sRGB alpha. The calculated alpha value was wrong. It's not clear if this affected the final stored value; in the obvious code path the upper and lower 8-bits of the alpha value were identical and the alpha was truncated to 8-bits rather than dividing by 257 (John Bowler).	2015-03-22 19:42:14 -05:00
Glenn Randers-Pehrson	b383798ac9	[libpng16] Add pnglibconf.dfn and pnglibconf.pre to scripts/pnglibconf.mak "clean" target.	2015-03-21 15:53:44 -05:00
Glenn Randers-Pehrson	ea037b01eb	[libpng16] Remove pnglibconf.dfn and pnglibconf.pre with "make clean".	2015-03-21 15:47:39 -05:00
Glenn Randers-Pehrson	04445235f1	[libpng16] Bump version to 1.6.17rc06	2015-03-21 12:11:10 -05:00
Glenn Randers-Pehrson	778ccbbafa	[libpng16] Imported from libpng-1.6.17rc05.tar	2015-03-21 12:11:00 -05:00
Glenn Randers-Pehrson	c5370ede95	[libpng16] Reverted "& 0xff" additions of version 1.6.17beta01. Libpng passes the Coverity scan without them.	2015-03-21 11:54:32 -05:00
John Bowler	2b66107abb	[libpng16] Define PNG_FILTER_* and PNG_FILTER_VALUE_* in png.h even when WRITE is not supported (John Bowler). This fixes an error introduced in libpng-1.6.17beta06.	2015-03-17 21:32:27 -05:00
Glenn Randers-Pehrson	0aabfe2a4c	[libpng16] Bump version to 1.6.17rc05	2015-03-17 08:14:23 -05:00
Glenn Randers-Pehrson	16f9246853	[libpng16] Imported from libpng-1.6.17rc04.tar	2015-03-17 08:00:12 -05:00
John Bowler	c9fd075c89	[libpng16] Fix bug in calculation of maxbits, in png_write_sBIT, introduced in libpng-1.6.17beta01 (John Bowler).	2015-03-16 16:31:13 -05:00
Cosmin Truta	47e1315459	[libpng16] Remove pnglibconf.h, pnglibconf.c, and pnglibconf.out instead of pnglibconf.* in "make clean" (Cosmin).	2015-03-15 17:04:17 -05:00
Glenn Randers-Pehrson	49fa8d4cdd	[libpng16] Bump version to 1.6.17rc04	2015-03-12 09:24:49 -05:00
Glenn Randers-Pehrson	a60de343a9	[libpng16] Imported from libpng-1.6.17rc03.tar	2015-03-12 06:49:06 -05:00
Glenn Randers-Pehrson	f2c37d0abf	[libpng16] Updated CMakeLists.txt to add OSX framework, change YES/NO to ON/OFF for consistency, and remove some useless tests (Alexey Petruchik).	2015-03-12 06:48:01 -05:00
Glenn Randers-Pehrson	bc27b2f432	[libpng16] Imported from libpng-1.6.17rc02.tar	2015-03-09 09:20:46 -05:00
Glenn Randers-Pehrson	3645008e22	[libpng16] Free the unknown_chunks structure even when it contains no data.	2015-03-09 09:13:58 -05:00
Glenn Randers-Pehrson	06ee532286	[libpng16] Reverted new test on unknown chunk location; it was bogus.	2015-03-08 08:00:45 -05:00
Glenn Randers-Pehrson	bbe2be3f54	[libpng16] Spelling fixes: less then N -> less than N (Lauri Nurmi)	2015-03-07 13:13:11 -06:00
Glenn Randers-Pehrson	bb098218ca	[libpng16] Fixed some spelling (occur* -> occurr*), Bug report by Lauri Nurmi	2015-03-07 12:59:48 -06:00
Glenn Randers-Pehrson	217d38cdea	[libpng16] Stopped a potential memory leak in png_set_unknown_chunks(). Breaks tests/pngunknown-sAPI so it's temporarily marked SKIP.	2015-03-07 10:35:03 -06:00
Glenn Randers-Pehrson	377fb53944	[libpng16] Removed some comments that the configure script did not handle properly from scripts/pnglibconf.dfa and pnglibconf.h.prebuilt.	2015-03-05 20:59:31 -06:00
Glenn Randers-Pehrson	7f85da8df7	[libpng16] Imported from libpng-1.6.17rc02.tar	2015-03-05 20:54:07 -06:00
Glenn Randers-Pehrson	3e0bef6da4	[libpng16] Imported from libpng-1.6.17rc01.tar	2015-03-04 11:19:32 -06:00
Glenn Randers-Pehrson	82511341d7	[libpng16] Bump version to 1.6.17beta07	2015-02-27 19:20:37 -06:00
Glenn Randers-Pehrson	4029db9aac	[libpng16] Imported from libpng-1.6.17beta06.tar	2015-02-27 19:01:02 -06:00
Glenn Randers-Pehrson	7011a8cec3	[libpng16] Added "& 0xff" to things being typecast to "png_byte".	2015-02-27 18:53:44 -06:00
Sergey Kosarevsky	9a3de48b48	[libpng16] Avoid runtime checks when converting integer to png_byte with Visual Studio (Sergey Kosarevsky)	2015-02-27 18:47:43 -06:00
Glenn Randers-Pehrson	494e75ac83	[libpng16] Fixed some typos in the pngfix usage message.	2015-02-26 10:39:13 -06:00
Glenn Randers-Pehrson	3f49c1e42a	[libpng16] Bump version to 1.6.17beta06	2015-02-25 15:42:16 -06:00