[libpng16] Revised INSTALL and libpng-manual.txt

ANNOUNCE

@@ -1,5 +1,5 @@
 
-Libpng 1.6.11beta01 - March 16, 2014
+Libpng 1.6.11beta01 - March 17, 2014
 
 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.
@@ -26,7 +26,7 @@ Other information:
 
 Changes since the last public release (1.6.10):
 
-Version 1.6.11beta01 [March 16, 2014]
+Version 1.6.11beta01 [March 17, 2014]
   Use "if (value != 0)" instead of "if (value)" consistently.
   Changed ZlibSrcDir from 1.2.5 to 1.2.8 in projects/vstudio.
   Moved configuration information from the manual to the INSTALL file.

CHANGES

@@ -4875,7 +4875,7 @@ Version 1.6.10rc03 [March 4, 2014]
 Version 1.6.10 [March 6, 2014]
   No changes.
 
-Version 1.6.11beta01 [March 16, 2014]
+Version 1.6.11beta01 [March 17, 2014]
   Use "if (value != 0)" instead of "if (value)" consistently.
   Changed ZlibSrcDir from 1.2.5 to 1.2.8 in projects/vstudio.
   Moved configuration information from the manual to the INSTALL file.

INSTALL

@@ -1,6 +1,27 @@
 
 Installing libpng
 
+Contents
+
+   I. Simple installation
+  II. Rebuilding the configure scripts
+ III. Using scripts/makefile*
+  IV. Using cmake
+   V. Directory structure
+  VI. Building with project files
+ VII. Building with makefiles
+VIII. Configuring libpng for 16-bit platforms
+  IX. Configuring for DOS
+  X. Configuring for Medium Model
+  XI. Prepending a prefix to exported symbols
+ XII. Configuring for compiler xxx:
+XIII Removing unwanted object code
+ XIV. Changes to the build and configuration of libpng in libpng-1.5.x
+  XV. Configuring libpng for multiprocessing
+ XVI. Other sources of information about libpng:
+
+I. Simple installation
+
 On Unix/Linux and similar systems, you can simply type
 
     ./configure [--prefix=/path]
@@ -9,6 +30,8 @@ On Unix/Linux and similar systems, you can simply type
 
 and ignore the rest of this document.
 
+II. Rebuilding the configure scripts
+
 If configure does not work on your system, or if you have a need to
 change configure.ac or Makefile.am, and you have a reasonably
 up-to-date set of tools, running ./autogen.sh in a git clone before
@@ -24,6 +47,8 @@ aren't using any of the included pre-built scripts, you can do this:
     make install
     make check
 
+III. Using scripts/makefile*
+
 Instead, you can use one of the custom-built makefiles in the
 "scripts" directory
 
@@ -41,19 +66,37 @@ is not already on your system.  zlib can usually be found
 wherever you got libpng.  zlib can be placed in another directory,
 at the same level as libpng.
 
+If your system already has a preinstalled zlib you will still need
+to have access to the zlib.h and zconf.h include files that
+correspond to the version of zlib that's installed.
+
+If you wish to test with a particular zlib that is not first in the
+standard library search path, put ZLIBLIB, ZLIBINC, CPPFLAGS, LDFLAGS,
+and LD_LIBRARY_PATH in your environment before running "make test"
+or "make distcheck":
+
+ZLIBLIB=/path/to/lib export ZLIBLIB
+ZLIBINC=/path/to/include export ZLIBINC
+CPPFLAGS="-I$ZLIBINC" export CPPFLAGS
+LDFLAGS="-L$ZLIBLIB" export LDFLAGS
+LD_LIBRARY_PATH="$ZLIBLIB:$LD_LIBRARY_PATH" export LD_LIBRARY_PATH
+
+If you are using one of the makefile scripts, put ZLIBLIB and ZLIBINC
+in your environment and type "make ZLIBLIB=$ZLIBLIB ZLIBINC=$ZLIBINC test".
+
+IV. Using cmake
+
 If you want to use "cmake" (see www.cmake.org), type
 
    cmake . -DCMAKE_INSTALL_PREFIX=/path
    make
    make install
 
-If your system already has a preinstalled zlib you will still need
+V. Directory structure
-to have access to the zlib.h and zconf.h include files that
-correspond to the version of zlib that's installed.
 
 You can rename the directories that you downloaded (they
-might be called "libpng-x.y.z" or "libpngNN" and "zlib-1.2.5"
+might be called "libpng-x.y.z" or "libpngNN" and "zlib-1.2.7"
-or "zlib125") so that you have directories called "zlib" and "libpng".
+or "zlib127") so that you have directories called "zlib" and "libpng".
 
 Your directory structure should look like this:
 
@@ -71,6 +114,7 @@ Your directory structure should look like this:
              depcomp, install-sh, mkinstalldirs, test-pngtest.sh
           contrib
              gregbook
+             libtests
              pngminim
              pngminus
              pngsuite
@@ -95,6 +139,8 @@ If the line endings in the files look funny, you may wish to get the other
 distribution of libpng.  It is available in both tar.gz (UNIX style line
 endings) and zip (DOS style line endings) formats.
 
+VI. Building with project files
+
 If you are building libpng with MSVC, you can enter the
 libpng projects\visualc6 or visualc71 directory and follow the instructions
 in README.txt.
@@ -103,6 +149,8 @@ Otherwise enter the zlib directory and follow the instructions in zlib/README,
 then come back here and run "configure" or choose the appropriate
 makefile.sys in the scripts directory.
 
+VII. Building with makefiles
+
 Copy the file (or files) that you need from the
 scripts directory into this directory, for example
 
@@ -130,6 +178,198 @@ do that, run "make install" in the zlib directory first if necessary).
 Some also allow you to run "make test-installed" after you have
 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
+won't be accessible.  So limit zlib and libpng to 64K by defining MAXSEG_64K.
+
+IX. Configuring for DOS
+
+For DOS users who only have access to the lower 640K, you will
+have to limit zlib's memory usage via a png_set_compression_mem_level()
+call.  See zlib.h or zconf.h in the zlib library for more information.
+
+X. Configuring for Medium Model
+
+Libpng's support for medium model has been tested on most of the popular
+compilers.  Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
+defined, and FAR gets defined to far in pngconf.h, and you should be
+all set.  Everything in the library (except for zlib's structure) is
+expecting far data.  You must use the typedefs with the p or pp on
+the end for pointers (or at least look at them and be careful).  Make
+note that the rows of data are defined as png_bytepp, which is
+an "unsigned char far * far *".
+
+XI. Prepending a prefix to exported symbols
+
+Starting with libpng-1.6.0, you can configure libpng (when using the
+"configure" script) to prefix all exported symbols by means of the
+configuration option "--with-libpng-prefix=FOO_", where FOO_ can be any
+string beginning with a letter and containing only uppercase
+and lowercase letters, digits, and the underscore (i.e., a C language
+identifier).  This creates a set of macros in pnglibconf.h, so this is
+transparent to applications; their function calls get transformed by
+the macros to use the modified names.
+
+XII. Configuring for compiler xxx:
+
+All includes for libpng are in pngconf.h.  If you need to add, change
+or delete an include, this is the place to do it.
+The includes that are not needed outside libpng are placed in pngpriv.h,
+which is only used by the routines inside libpng itself.
+The files in libpng proper only include pngpriv.h and png.h, which
+in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
+As of libpng-1.5.0, pngpriv.h also includes three other private header
+files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
+that previously appeared in the public headers.
+
+XIII. Removing unwanted object code
+
+There are a bunch of #define's in pngconf.h that control what parts of
+libpng are compiled.  All the defines end in _SUPPORTED.  If you are
+never going to use a capability, you can change the #define to #undef
+before recompiling libpng and save yourself code and data space, or
+you can turn off individual capabilities with defines that begin with
+PNG_NO_.
+
+In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
+
+You can also turn all of the transforms and ancillary chunk capabilities
+off en masse with compiler directives that define
+PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
+or all four, along with directives to turn on any of the capabilities that
+you do want.  The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the
+extra transformations but still leave the library fully capable of reading
+and writing PNG files with all known public chunks. Use of the
+PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
+that is incapable of reading or writing ancillary chunks.  If you are
+not using the progressive reading capability, you can turn that off
+with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
+capability, which you'll still have).
+
+All the reading and writing specific code are in separate files, so the
+linker should only grab the files it needs.  However, if you want to
+make sure, or if you are building a stand alone library, all the
+reading files start with "pngr" and all the writing files start with "pngw".
+The files that don't match either (like png.c, pngtrans.c, etc.)
+are used for both reading and writing, and always need to be included.
+The progressive reader is in pngpread.c
+
+If you are creating or distributing a dynamically linked library (a .so
+or DLL file), you should not remove or disable any parts of the library,
+as this will cause applications linked with different versions of the
+library to fail if they call functions not available in your library.
+The size of the library itself should not be an issue, because only
+those sections that are actually used will be loaded into memory.
+
+XIV. Changes to the build and configuration of libpng in libpng-1.5.x
+
+Details of internal changes to the library code can be found in the CHANGES
+file and in the GIT repository logs.  These will be of no concern to the vast
+majority of library users or builders; however, the few who configure libpng
+to a non-default feature set may need to change how this is done.
+
+There should be no need for library builders to alter build scripts if
+these use the distributed build support - configure or the makefiles -
+however, users of the makefiles may care to update their build scripts
+to build pnglibconf.h where the corresponding makefile does not do so.
+
+Building libpng with a non-default configuration has changed completely.
+The old method using pngusr.h should still work correctly even though the
+way pngusr.h is used in the build has been changed; however, library
+builders will probably want to examine the changes to take advantage of
+new capabilities and to simplify their build system.
+
+A. Specific changes to library configuration capabilities
+
+The library now supports a complete fixed point implementation and can
+thus be used on systems that have no floating point support or very
+limited or slow support.  Previously gamma correction, an essential part
+of complete PNG support, required reasonably fast floating point.
+
+As part of this the choice of internal implementation has been made
+independent of the choice of fixed versus floating point APIs and all the
+missing fixed point APIs have been implemented.
+
+The exact mechanism used to control attributes of API functions has
+changed.  A single set of operating system independent macro definitions
+is used and operating system specific directives are defined in
+pnglibconf.h
+
+As part of this the mechanism used to choose procedure call standards on
+those systems that allow a choice has been changed.  At present this only
+affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
+running on Intel processors.  As before, PNGAPI is defined where required
+to control the exported API functions; however, two new macros, PNGCBAPI
+and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
+(PNGCAPI) for functions that must match a C library prototype (currently
+only png_longjmp_ptr, which must match the C longjmp function.)  The new
+approach is documented in pngconf.h
+
+Despite these changes, libpng 1.5.0 only supports the native C function
+calling standard on those platforms tested so far (__cdecl on Microsoft
+Windows).  This is because the support requirements for alternative
+calling conventions seem to no longer exist.  Developers who find it
+necessary to set PNG_API_RULE to 1 should advise the mailing list
+(png-mng-implement) of this and library builders who use Openwatcom and
+therefore set PNG_API_RULE to 2 should also contact the mailing list.
+
+B. Changes to the configuration mechanism
+
+Prior to libpng-1.5.0 library builders who needed to configure libpng
+had either to modify the exported pngconf.h header file to add system
+specific configuration or had to write feature selection macros into
+pngusr.h and cause this to be included into pngconf.h by defining
+PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
+application built without PNG_USER_CONFIG defined would see the
+unmodified, default, libpng API and thus would probably fail to link.
+
+These mechanisms still work in the configure build and in any makefile
+build that builds pnglibconf.h, although the feature selection macros
+have changed somewhat as described above.  In 1.5.0, however, pngusr.h is
+processed only once, when the exported header file pnglibconf.h is built.
+pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
+build of pnglibconf.h and it is never included in an application build.
+
+The rarely used alternative of adding a list of feature macros to the
+CPPFLAGS setting in the build also still works; however, the macros will be
+copied to pnglibconf.h and this may produce macro redefinition warnings
+when the individual C files are compiled.
+
+All configuration now only works if pnglibconf.h is built from
+scripts/pnglibconf.dfa.  This requires the program awk.  Brian Kernighan
+(the original author of awk) maintains C source code of that awk and this
+and all known later implementations (often called by subtly different
+names - nawk and gawk for example) are adequate to build pnglibconf.h.
+The Sun Microsystems (now Oracle) program 'awk' is an earlier version
+and does not work; this may also apply to other systems that have a
+functioning awk called 'nawk'.
+
+Configuration options are now documented in scripts/pnglibconf.dfa.  This
+file also includes dependency information that ensures a configuration is
+consistent; that is, if a feature is switched off dependent features are
+also removed.  As a recommended alternative to using feature macros in
+pngusr.h a system builder may also define equivalent options in pngusr.dfa
+(or, indeed, any file) and add that to the configuration by setting
+DFA_XTRA to the file name.  The makefiles in contrib/pngminim illustrate
+how to do this, and a case where pngusr.h is still required.
+
+XV. Configuring libpng for multiprocessing
+
+Libpng uses setjmp()/longjmp() for error handling.  Unfortunately setjmp()
+is known to be not thread-safe on some platforms and we don't know of
+any platform where it is guaranteed to be thread-safe.  Therefore, if
+your application is going to be using multiple threads, you should
+configure libpng with PNG_NO_SETJMP in your pngusr.dfa file, with
+-DPNG_NO_SETJMP on your compile line, or with
+
+  #undef PNG_SETJMP_SUPPORTED
+
+in your pnglibconf.h or pngusr.h.
+
+XVI. Other sources of information about libpng:
+
 Further information can be found in the README and libpng-manual.txt
 files, in the individual makefiles, in png.h, and the manual pages
 libpng.3 and png.5.

libpng-manual.txt

@@ -1,9 +1,9 @@
 libpng-manual.txt - A description on how to use and modify libpng
 
- libpng version 1.6.1beta01 - February 16, 2013
+ libpng version 1.6.11beta01 - March 17, 2014
  Updated and distributed by Glenn Randers-Pehrson
  <glennrp at users.sourceforge.net>
- Copyright (c) 1998-2013 Glenn Randers-Pehrson
+ Copyright (c) 1998-2014 Glenn Randers-Pehrson
 
  This document is released under the libpng license.
  For conditions of distribution and use, see the disclaimer
@@ -11,9 +11,9 @@ libpng-manual.txt - A description on how to use and modify libpng
 
  Based on:
 
- libpng versions 0.97, January 1998, through 1.6.1beta01 - February 16, 2013
+ libpng versions 0.97, January 1998, through 1.6.11beta01 - March 17, 2014
  Updated and distributed by Glenn Randers-Pehrson
- Copyright (c) 1998-2013 Glenn Randers-Pehrson
+ Copyright (c) 1998-2014 Glenn Randers-Pehrson
 
  libpng 1.0 beta 6  version 0.96 May 28, 1997
  Updated and distributed by Andreas Dilger
@@ -50,13 +50,11 @@ libpng-manual.txt - A description on how to use and modify libpng
 I. Introduction
 
 This file describes how to use and modify the PNG reference library
-(known as libpng) for your own use.  There are five sections to this
+(known as libpng) for your own use.  In addition to this
-file: introduction, structures, reading, writing, and modification and
-configuration notes for various special platforms.  In addition to this
 file, example.c is a good starting point for using the library, as
 it is heavily commented and should include everything most people
 will need.  We assume that libpng is already installed; see the
-INSTALL file for instructions on how to install libpng.
+INSTALL file for instructions on how to configure and install libpng.
 
 For examples of libpng usage, see the files "example.c", "pngtest.c",
 and the files in the "contrib" directory, all of which are included in
@@ -276,10 +274,10 @@ This method of building a customized pnglibconf.h is illustrated in
 contrib/pngminim/*.  See the "$(PNGCONF):" target in the makefile and
 pngusr.dfa in these directories.
 
-C. Configuration using PNG_USR_CONFIG
+C. Configuration using PNG_USER_CONFIG
 
-If -DPNG_USR_CONFIG is added to the CFLAGS when pnglibconf.h is built the file
+If -DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
-pngusr.h will automatically be included before the options in
+the file pngusr.h will automatically be included before the options in
 scripts/pnglibconf.dfa are processed.  Your pngusr.h file should contain only
 macro definitions turning features on or off or setting settings.
 
@@ -527,9 +525,14 @@ you can retrieve with
     png_get_user_chunk_ptr(png_ptr);
 
 If you call the png_set_read_user_chunk_fn() function, then all unknown
-chunks will be saved when read, in case your callback function will need
+chunks which the callback does not handle will be saved when read.  You can
-one or more of them.  This behavior can be changed with the
+cause them to be discarded by returning '1' ("handled") instead of '0'.  This
-png_set_keep_unknown_chunks() function, described below.
+behavior will change in libpng 1.7 and the default handling set by the
+png_set_keep_unknown_chunks() function, described below, will be used when the
+callback returns 0.  If you want the existing behavior you should set the global
+default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
+versions of libpng and with 1.7.  Libpng 1.6 issues a warning if you keep the
+default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
 
 At this point, you can set up a callback function that will be
 called after each row has been read, which you can use to control
@@ -628,15 +631,17 @@ callback function:
     ...
 
     #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
-      /* ignore all unknown chunks: */
+      /* ignore all unknown chunks
-      png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
+       * (use global setting "2" for libpng16 and earlier):
+       */
+      png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
 
       /* except for vpAg: */
       png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
 
       /* also ignore unused known chunks: */
       png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
-         (int)sizeof(unused_chunks)/5);
+         (int)(sizeof unused_chunks)/5);
     #endif
 
 User limits
@@ -707,12 +712,12 @@ value.  You can also specify a default encoding for the PNG file in
 case the required information is missing from the file.  By default libpng
 assumes that the PNG data matches your system, to keep this default call:
 
-   png_set_gamma(png_ptr, screen_gamma, 1/screen_gamma/*file gamma*/);
+   png_set_gamma(png_ptr, screen_gamma, output_gamma);
 
 or you can use the fixed point equivalent:
 
    png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
-      PNG_FP_1/screen_gamma);
+      PNG_FP_1*output_gamma);
 
 If you don't know the gamma for your system it is probably 2.2 - a good
 approximation to the IEC standard for display systems (sRGB).  If images are
@@ -735,11 +740,75 @@ situations:
                      encoding.
 
 You would use the linear (unencoded) value if you need to process the pixel
-values further because this avoids the need to decode and reencode each
+values further because this avoids the need to decode and re-encode each
 component value whenever arithmetic is performed.  A lot of graphics software
 uses linear values for this reason, often with higher precision component values
 to preserve overall accuracy.
 
+
+The output_gamma value expresses how to decode the output values, not how
+they are encoded.  The values used correspond to the normal numbers used to
+describe the overall gamma of a computer display system; for example 2.2 for
+an sRGB conformant system.  The values are scaled by 100000 in the _fixed
+version of the API (so 220000 for sRGB.)
+
+The inverse of the value is always used to provide a default for the PNG file
+encoding if it has no gAMA chunk and if png_set_gamma() has not been called
+to override the PNG gamma information.
+
+When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
+opaque pixels however pixels with lower alpha values are not encoded,
+regardless of the output gamma setting.
+
+When the standard Porter Duff handling is requested with mode 1 the output
+encoding is set to be linear and the output_gamma value is only relevant
+as a default for input data that has no gamma information.  The linear output
+encoding will be overridden if png_set_gamma() is called - the results may be
+highly unexpected!
+
+The following numbers are derived from the sRGB standard and the research
+behind it.  sRGB is defined to be approximated by a PNG gAMA chunk value of
+0.45455 (1/2.2) for PNG.  The value implicitly includes any viewing
+correction required to take account of any differences in the color
+environment of the original scene and the intended display environment; the
+value expresses how to *decode* the image for display, not how the original
+data was *encoded*.
+
+sRGB provides a peg for the PNG standard by defining a viewing environment.
+sRGB itself, and earlier TV standards, actually use a more complex transform
+(a linear portion then a gamma 2.4 power law) than PNG can express.  (PNG is
+limited to simple power laws.)  By saying that an image for direct display on
+an sRGB conformant system should be stored with a gAMA chunk value of 45455
+(11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
+makes it possible to derive values for other display systems and
+environments.
+
+The Mac value is deduced from the sRGB based on an assumption that the actual
+extra viewing correction used in early Mac display systems was implemented as
+a power 1.45 lookup table.
+
+Any system where a programmable lookup table is used or where the behavior of
+the final display device characteristics can be changed requires system
+specific code to obtain the current characteristic.  However this can be
+difficult and most PNG gamma correction only requires an approximate value.
+
+By default, if png_set_alpha_mode() is not called, libpng assumes that all
+values are unencoded, linear, values and that the output device also has a
+linear characteristic.  This is only very rarely correct - it is invariably
+better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
+default if you don't know what the right answer is!
+
+The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
+10.6) which used a correction table to implement a somewhat lower gamma on an
+otherwise sRGB system.
+
+Both these values are reserved (not simple gamma values) in order to allow
+more precise correction internally in the future.
+
+NOTE: the values can be passed to either the fixed or floating
+point APIs, but the floating point API will also accept floating point
+values.
+
 The second thing you may need to tell libpng about is how your system handles
 alpha channel information.  Some, but not all, PNG files contain an alpha
 channel.  To display these files correctly you need to compose the data onto a
@@ -764,11 +833,11 @@ by png_set_alpha_mode().
 
 The mode is as follows:
 
-    PNG_ALPHA_PNG: The data is encoded according to the PNG specification.  Red,
+    PNG_ALPHA_PNG: The data is encoded according to the PNG
-green and blue, or gray, components are gamma encoded color
+specification.  Red, green and blue, or gray, components are
-values and are not premultiplied by the alpha value.  The
+gamma encoded color values and are not premultiplied by the
-alpha value is a linear measure of the contribution of the
+alpha value.  The alpha value is a linear measure of the
-pixel to the corresponding final output pixel.
+contribution of the pixel to the corresponding final output pixel.
 
 You should normally use this format if you intend to perform
 color correction on the color values; most, maybe all, color
@@ -785,11 +854,35 @@ be used!
 
 The remaining modes assume you don't need to do any further color correction or
 that if you do, your color correction software knows all about alpha (it
-probably doesn't!)
+probably doesn't!).  They 'associate' the alpha with the color information by
+storing color channel values that have been scaled by the alpha.  The
+advantage is that the color channels can be resampled (the image can be
+scaled) in this form.  The disadvantage is that normal practice is to store
+linear, not (gamma) encoded, values and this requires 16-bit channels for
+still images rather than the 8-bit channels that are just about sufficient if
+gamma encoding is used.  In addition all non-transparent pixel values,
+including completely opaque ones, must be gamma encoded to produce the final
+image.  These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
+described below (the latter being the two common names for associated alpha
+color channels). Note that PNG files always contain non-associated color
+channels; png_set_alpha_mode() with one of the modes causes the decoder to
+convert the pixels to an associated form before returning them to your
+application. 
 
-    PNG_ALPHA_STANDARD:  The data libpng produces
+Since it is not necessary to perform arithmetic on opaque color values so
-is encoded in the standard way
+long as they are not to be resampled and are in the final color space it is
-assumed by most correctly written graphics software.
+possible to optimize the handling of alpha by storing the opaque pixels in
+the PNG format (adjusted for the output color space) while storing partially
+opaque pixels in the standard, linear, format.  The accuracy required for
+standard alpha composition is relatively low, because the pixels are
+isolated, therefore typically the accuracy loss in storing 8-bit linear
+values is acceptable.  (This is not true if the alpha channel is used to
+simulate transparency over large areas - use 16 bits or the PNG mode in
+this case!)  This is the 'OPTIMIZED' mode.  For this mode a pixel is
+treated as opaque only if the alpha value is equal to the maximum value.
+
+    PNG_ALPHA_STANDARD:  The data libpng produces is encoded in the
+standard way assumed by most correctly written graphics software.
 The gamma encoding will be removed by libpng and the
 linear component values will be pre-multiplied by the
 alpha channel.
@@ -818,9 +911,8 @@ dynamic range.  To avoid problems, and if your software
 supports it, use png_set_expand_16() to force all
 components to 16 bits.
 
-    PNG_ALPHA_OPTIMIZED: This mode is the same
+    PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
-as PNG_ALPHA_STANDARD except that
+except that completely opaque pixels are gamma encoded according to
-completely opaque pixels are gamma encoded according to
 the screen_gamma value.  Pixels with alpha less than 1.0
 will still have linear components.
 
@@ -839,18 +931,16 @@ representation of non-opaque pixels are irrelevant.
 You can also try this format if your software is broken;
 it might look better.
 
-    PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD;
+    PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
-however, all component values,
+values, including the alpha channel are gamma encoded.  This is
-including the alpha channel are gamma encoded.  This is
+broken because, in practice, no implementation that uses this choice
-an appropriate format to try if your software, or more
+correctly undoes the encoding before handling alpha composition.  Use this
-likely hardware, is totally broken, i.e., if it performs
+choice only if other serious errors in the software or hardware you use
-linear arithmetic directly on gamma encoded values.
+mandate it.  In most cases of broken software or hardware the bug in the
-
+final display manifests as a subtle halo around composited parts of the
-In most cases of broken software or hardware the bug in the final display
+image.  You may not even perceive this as a halo; the composited part of
-manifests as a subtle halo around composited parts of the image.  You may not
+the image may simply appear separate from the background, as though it had
-even perceive this as a halo; the composited part of the image may simply appear
+been cut out of paper and pasted on afterward.
-separate from the background, as though it had been cut out of paper and pasted
-on afterward.
 
 If you don't have to deal with bugs in software or hardware, or if you can fix
 them, there are three recommended ways of using png_set_alpha_mode():
@@ -881,6 +971,89 @@ All you can do is compose the result onto a matching output.  Since this
 mode is libpng-specific you also need to write your own composition
 software.
 
+The following are examples of calls to png_set_alpha_mode to achieve the
+required overall gamma correction and, where necessary, alpha
+premultiplication.
+
+    png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
+
+This is the default libpng handling of the alpha channel - it is not
+pre-multiplied into the color components.  In addition the call states
+that the output is for a sRGB system and causes all PNG files without gAMA
+chunks to be assumed to be encoded using sRGB.
+
+    png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
+
+In this case the output is assumed to be something like an sRGB conformant
+display preceeded by a power-law lookup table of power 1.45.  This is how
+early Mac systems behaved.
+
+    png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
+
+This is the classic Jim Blinn approach and will work in academic
+environments where everything is done by the book.  It has the shortcoming
+of assuming that input PNG data with no gamma information is linear - this
+is unlikely to be correct unless the PNG files where generated locally.
+Most of the time the output precision will be so low as to show
+significant banding in dark areas of the image.
+
+    png_set_expand_16(pp);
+    png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
+
+This is a somewhat more realistic Jim Blinn inspired approach.  PNG files
+are assumed to have the sRGB encoding if not marked with a gamma value and
+the output is always 16 bits per component.  This permits accurate scaling
+and processing of the data.  If you know that your input PNG files were
+generated locally you might need to replace PNG_DEFAULT_sRGB with the
+correct value for your system.
+
+    png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
+
+If you just need to composite the PNG image onto an existing background
+and if you control the code that does this you can use the optimization
+setting.  In this case you just copy completely opaque pixels to the
+output.  For pixels that are not completely transparent (you just skip
+those) you do the composition math using png_composite or png_composite_16
+below then encode the resultant 8-bit or 16-bit values to match the output
+encoding.
+
+    Other cases
+
+If neither the PNG nor the standard linear encoding work for you because
+of the software or hardware you use then you have a big problem.  The PNG
+case will probably result in halos around the image.  The linear encoding
+will probably result in a washed out, too bright, image (it's actually too
+contrasty.)  Try the ALPHA_OPTIMIZED mode above - this will probably
+substantially reduce the halos.  Alternatively try:
+
+    png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
+
+This option will also reduce the halos, but there will be slight dark
+halos round the opaque parts of the image where the background is light.
+In the OPTIMIZED mode the halos will be light halos where the background
+is dark.  Take your pick - the halos are unavoidable unless you can get
+your hardware/software fixed!  (The OPTIMIZED approach is slightly
+faster.)
+
+When the default gamma of PNG files doesn't match the output gamma.
+If you have PNG files with no gamma information png_set_alpha_mode allows
+you to provide a default gamma, but it also sets the ouput gamma to the
+matching value.  If you know your PNG files have a gamma that doesn't
+match the output you can take advantage of the fact that
+png_set_alpha_mode always sets the output gamma but only sets the PNG
+default if it is not already set:
+
+    png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
+    png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
+
+The first call sets both the default and the output gamma values, the
+second call overrides the output gamma without changing the default.  This
+is easier than achieving the same effect with png_set_gamma.  You must use
+PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
+fire if more than one call to png_set_alpha_mode and png_set_background is
+made in the same read operation, however multiple calls with PNG_ALPHA_PNG
+are ignored.
+
 If you don't need, or can't handle, the alpha channel you can call
 png_set_background() to remove it by compositing against a fixed color.  Don't
 call png_set_strip_alpha() to do this - it will leave spurious pixel values in
@@ -988,7 +1161,7 @@ where row_pointers is an array of pointers to the pixel data for each row:
 If you know your image size and pixel size ahead of time, you can allocate
 row_pointers prior to calling png_read_png() with
 
-   if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
+   if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
       png_error (png_ptr,
           "Image is too tall to process in memory");
 
@@ -997,7 +1170,7 @@ row_pointers prior to calling png_read_png() with
           "Image is too wide to process in memory");
 
    row_pointers = png_malloc(png_ptr,
-       height*png_sizeof(png_bytep));
+       height*(sizeof (png_bytep)));
 
    for (int i=0; i<height, i++)
       row_pointers[i]=NULL;  /* security precaution */
@@ -1211,7 +1384,7 @@ png_set_rgb_to_gray()).
 
     png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
 
-    file_srgb_intent - the rendering intent (PNG_INFO_sRGB)
+    srgb_intent -    the rendering intent (PNG_INFO_sRGB)
                      The presence of the sRGB chunk
                      means that the pixel data is in the
                      sRGB color space.  This chunk also
@@ -2161,10 +2334,15 @@ how pngvalid.c does it.
 Finishing a sequential read
 
 After you are finished reading the image through the
-low-level interface, you can finish reading the file.  If you are
+low-level interface, you can finish reading the file.
-interested in comments or time, which may be stored either before or
+
-after the image data, you should pass the separate png_info struct if
+If you want to use a different crc action for handling CRC errors in
-you want to keep the comments from before and after the image
+chunks after the image data, you can call png_set_crc_action()
+again at this point.
+
+If you are interested in comments or time, which may be stored either
+before or after the image data, you should pass the separate png_info
+struct if you want to keep the comments from before and after the image
 separate.
 
     png_infop end_info = png_create_info_struct(png_ptr);
@@ -2180,6 +2358,9 @@ separate.
 
 If you are not interested, you should still call png_read_end()
 but you can pass NULL, avoiding the need to create an end_info structure.
+If you do this, libpng will not process any chunks after IDAT other than
+skipping over them and perhaps (depending on whether you have called
+png_set_crc_action) checking their CRCs while looking for the IEND chunk.
 
    png_read_end(png_ptr, (png_infop)NULL);
 
@@ -2284,7 +2465,7 @@ For a more compact example of reading a PNG image, see the file example.c.
 
 Reading PNG files progressively
 
-The progressive reader is slightly different then the non-progressive
+The progressive reader is slightly different from the non-progressive
 reader.  Instead of calling png_read_info(), png_read_rows(), and
 png_read_end(), you make one call to png_process_data(), which calls
 callbacks when it has the info, a row, or the end of the image.  You
@@ -2455,7 +2636,7 @@ png_infop info_ptr;
         png_progressive_combine_row(png_ptr, old_row,
           new_row);
 
-    /* where old_row is what was displayed for
+    /* where old_row is what was displayed
        previously for the row.  Note that the first
        pass (pass == 0, really) will completely cover
        the old row, so the rows do not have to be
@@ -3086,13 +3267,47 @@ a writeable buffer of at least 29 bytes.
 
 Writing unknown chunks
 
-You can use the png_set_unknown_chunks function to queue up chunks
+You can use the png_set_unknown_chunks function to queue up private chunks
-for writing.  You give it a chunk name, raw data, and a size; that's
+for writing.  You give it a chunk name, location, raw data, and a size.  You
-all there is to it.  The chunks will be written by the next following
+also must use png_set_keep_unknown_chunks() to ensure that libpng will
-png_write_info_before_PLTE, png_write_info, or png_write_end function.
+handle them.  That's all there is to it.  The chunks will be written by the
-Any chunks previously read into the info structure's unknown-chunk
+next following png_write_info_before_PLTE, png_write_info, or png_write_end
-list will also be written out in a sequence that satisfies the PNG
+function, depending upon the specified location.  Any chunks previously
-specification's ordering rules.
+read into the info structure's unknown-chunk list will also be written out
+in a sequence that satisfies the PNG specification's ordering rules.
+
+Here is an example of writing two private chunks, prVt and miNE:
+
+    #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
+    /* Set unknown chunk data */
+    png_unknown_chunk unk_chunk[2];
+    strcpy((char *) unk_chunk[0].name, "prVt";
+    unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
+    unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
+    unk_chunk[0].location = PNG_HAVE_IHDR;
+    strcpy((char *) unk_chunk[1].name, "miNE";
+    unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
+    unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
+    unk_chunk[1].location = PNG_AFTER_IDAT;
+    png_set_unknown_chunks(write_ptr, write_info_ptr,
+        unk_chunk, 2);
+    /* Needed because miNE is not safe-to-copy */
+    png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
+       (png_bytep) "miNE", 1);
+    # if PNG_LIBPNG_VER < 10600
+      /* Deal with unknown chunk location bug in 1.5.x and earlier */
+      png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
+      png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
+    # endif
+    # if PNG_LIBPNG_VER < 10500
+      /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
+       * one before IDAT and another after IDAT, so don't use it; only use
+       * PNG_HAVE_IHDR location.  This call resets the location previously
+       * set by assignment and png_set_unknown_chunk_location() for chunk 1.
+       */
+      png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
+    # endif
+    #endif
 
 The high-level write interface
 
@@ -3496,7 +3711,7 @@ The simplified API, which became available in libpng-1.6.0, hides the details
 of both libpng and the PNG file format itself.
 It allows PNG files to be read into a very limited number of
 in-memory bitmap formats or to be written from the same formats.  If these
-formats do not accomodate your needs then you can, and should, use the more
+formats do not accommodate your needs then you can, and should, use the more
 sophisticated APIs above - these support a wide variety of in-memory formats
 and a wide variety of sophisticated transformations to those formats as well
 as a wide variety of APIs to manipulate ancilliary information.
@@ -3578,8 +3793,9 @@ and matches the 8-bit format expected by typical display devices.
 The color/gray channels are not scaled (pre-multiplied) by the alpha
 channel and are suitable for passing to color management software.
 
-  b) As a value in the range 0..65535, contained in a 2-byte integer.  All
+  b) As a value in the range 0..65535, contained in a 2-byte integer, in
-channels can be converted to the original value by dividing by 65535; all
+the native byte order of the platform on which the application is running.
+All channels can be converted to the original value by dividing by 65535; all
 channels are linear.  Color channels use the RGB encoding (RGB end-points) of
 the sRGB specification.  This encoding is identified by the
 PNG_FORMAT_FLAG_LINEAR flag below.
@@ -3646,7 +3862,9 @@ First the single byte formats:
 Then the linear 2-byte formats.  When naming these "Y" is used to
 indicate a luminance (gray) channel.  The component order within the pixel
 is always the same - there is no provision for swapping the order of the
-components in the linear format.
+components in the linear format.  The components are 16-bit integers in
+the native byte order for your platform, and there is no provision for
+swapping the bytes to a different endian condition.
 
    PNG_FORMAT_LINEAR_Y PNG_FORMAT_FLAG_LINEAR
    PNG_FORMAT_LINEAR_Y_ALPHA
@@ -3711,7 +3929,7 @@ First the information about the samples.
     *
     * png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
     *
-    * Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
+    * Alternatively, use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
     * information from one of the png_image_begin_read_ APIs and dynamically
     * allocate the required memory.
     */
@@ -3740,9 +3958,16 @@ Information about the whole row, or whole image
    row.  For a color-mapped image this is the minimum number of bytes in a
    row.
 
+   If you need the stride measured in bytes, row_stride_bytes is
+   PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)
+   plus any padding bytes that your application might need, for example
+   to start the next row on a 4-byte boundary.
+
   PNG_IMAGE_BUFFER_SIZE(image, row_stride)
     Returns the size, in bytes, of an image buffer given a png_image and a row
-    stride - the number of components to leave space for in each row.
+    stride - the number of components to leave space for in each row.  This
+    macro takes care of multiplying row_stride by PNG_IMAGE_PIXEL_COMONENT_SIZE
+    when the image has 2-byte components.
 
   PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
     This indicates the the RGB values of the in-memory bitmap do not
@@ -3871,14 +4096,11 @@ clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
 is not the same as the calloc(number, size) function provided by stdlib.h.
 There is limited support for certain systems with segmented memory
 architectures and the types of pointers declared by png.h match this; you
-will have to use appropriate pointers in your application.  Since it is
+will have to use appropriate pointers in your application.  If you prefer
-unlikely that the method of handling memory allocation on a platform
+to use a different method of allocating and freeing data, you can use
-will change between applications, these functions must be modified in
+png_create_read_struct_2() or png_create_write_struct_2() to register your
-the library at compile time.  If you prefer to use a different method
+own functions as described above.  These functions also provide a void
-of allocating and freeing data, you can use png_create_read_struct_2() or
+pointer that can be retrieved via
-png_create_write_struct_2() to register your own functions as described
-above.  These functions also provide a void pointer that can be retrieved
-via
 
     mem_ptr=png_get_mem_ptr(png_ptr);
 
@@ -3987,9 +4209,12 @@ as warnings.
 
     png_set_benign_errors (png_ptr, int allowed);
 
-    allowed: 0: (default) treat png_benign_error() an error.
+    allowed: 0: treat png_benign_error() as an error.
              1: treat png_benign_error() as a warning.
 
+As of libpng-1.6.0, the default condition is to treat benign errors as
+warnings while reading and as errors while writing.
+
 Custom chunks
 
 If you need to read or write custom chunks, you may need to get deeper
@@ -4018,29 +4243,6 @@ the simpler ones to get an idea of how they work.  Try to find a similar
 transformation to the one you want to add and copy off of it.  More details
 can be found in the comments inside the code itself.
 
-Configuring 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
-won't be accessible.  So limit zlib and libpng to 64K by defining MAXSEG_64K.
-
-Configuring for DOS
-
-For DOS users who only have access to the lower 640K, you will
-have to limit zlib's memory usage via a png_set_compression_mem_level()
-call.  See zlib.h or zconf.h in the zlib library for more information.
-
-Configuring for Medium Model
-
-Libpng's support for medium model has been tested on most of the popular
-compilers.  Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
-defined, and FAR gets defined to far in pngconf.h, and you should be
-all set.  Everything in the library (except for zlib's structure) is
-expecting far data.  You must use the typedefs with the p or pp on
-the end for pointers (or at least look at them and be careful).  Make
-note that the rows of data are defined as png_bytepp, which is
-an "unsigned char far * far *".
-
 Configuring for gui/windowing platforms:
 
 You will need to write new error and warning functions that use the GUI
@@ -4050,18 +4252,6 @@ in order to have them available during the structure initialization.
 They can be changed later via png_set_error_fn().  On some compilers,
 you may also have to change the memory allocators (png_malloc, etc.).
 
-Configuring for compiler xxx:
-
-All includes for libpng are in pngconf.h.  If you need to add, change
-or delete an include, this is the place to do it.
-The includes that are not needed outside libpng are placed in pngpriv.h,
-which is only used by the routines inside libpng itself.
-The files in libpng proper only include pngpriv.h and png.h, which
-in turn includes pngconf.h and, as of libpng-1.5.0, pnglibconf.h.
-As of libpng-1.5.0, pngpriv.h also includes three other private header
-files, pngstruct.h, pnginfo.h, and pngdebug.h, which contain material
-that previously appeared in the public headers.
-
 Configuring zlib:
 
 There are special functions to configure the compression.  Perhaps the
@@ -4201,46 +4391,6 @@ Note that the numbers above were invented purely for this example and
 are given only to help explain the function usage.  Little testing has
 been done to find optimum values for either the costs or the weights.
 
-Removing unwanted object code
-
-There are a bunch of #define's in pngconf.h that control what parts of
-libpng are compiled.  All the defines end in _SUPPORTED.  If you are
-never going to use a capability, you can change the #define to #undef
-before recompiling libpng and save yourself code and data space, or
-you can turn off individual capabilities with defines that begin with
-PNG_NO_.
-
-In libpng-1.5.0 and later, the #define's are in pnglibconf.h instead.
-
-You can also turn all of the transforms and ancillary chunk capabilities
-off en masse with compiler directives that define
-PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
-or all four,
-along with directives to turn on any of the capabilities that you do
-want.  The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
-transformations but still leave the library fully capable of reading
-and writing PNG files with all known public chunks. Use of the
-PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
-that is incapable of reading or writing ancillary chunks.  If you are
-not using the progressive reading capability, you can turn that off
-with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
-capability, which you'll still have).
-
-All the reading and writing specific code are in separate files, so the
-linker should only grab the files it needs.  However, if you want to
-make sure, or if you are building a stand alone library, all the
-reading files start with "pngr" and all the writing files start with "pngw".
-The files that don't match either (like png.c, pngtrans.c, etc.)
-are used for both reading and writing, and always need to be included.
-The progressive reader is in pngpread.c
-
-If you are creating or distributing a dynamically linked library (a .so
-or DLL file), you should not remove or disable any parts of the library,
-as this will cause applications linked with different versions of the
-library to fail if they call functions not available in your library.
-The size of the library itself should not be an issue, because only
-those sections that are actually used will be loaded into memory.
-
 Requesting debug printout
 
 The macro definition PNG_DEBUG can be used to request debugging
@@ -4260,7 +4410,7 @@ the message, "message" is the formatted string to be printed,
 and p1 and p2 are parameters that are to be embedded in the string
 according to printf-style formatting directives.  For example,
 
-   png_debug1(2, "foo=%d\n", foo);
+   png_debug1(2, "foo=%d", foo);
 
 is expanded to
 
@@ -4278,17 +4428,6 @@ When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
 having level = 0 will be printed.  There aren't any such statements in
 this version of libpng, but if you insert some they will be printed.
 
-Prepending a prefix to exported symbols
-
-Starting with libpng-1.6.0, you can configure libpng (when using the
-"configure" script) to prefix all exported symbols by means of the
-configuration option "--with-libpng-prefix=FOO_", where FOO_ can be any
-string beginning with a letter and containing only uppercase
-and lowercase letters, digits, and the underscore (i.e., a C language
-identifier).  This creates a set of macros in pnglibconf.h, so this is
-transparent to applications; their function calls get transformed by
-the macros to use the modified names.
-
 VII.  MNG support
 
 The MNG specification (available at http://www.libpng.org/pub/mng) allows
@@ -4351,6 +4490,9 @@ png_set_error_fn(), which is essentially the same function, but with a new
 name to force compilation errors with applications that try to use the old
 method.
 
+Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
+however, iTXt support was not enabled by default.
+
 Starting with version 1.0.7, you can find out which version of the library
 you are using at run-time:
 
@@ -4567,7 +4709,7 @@ it has not been well tested and doesn't actually "dither".
 The code was not
 removed, however, and could be enabled by building libpng with
 PNG_READ_DITHER_SUPPORTED defined.  In libpng-1.4.2, this support
-was reenabled, but the function was renamed png_set_quantize() to
+was re-enabled, but the function was renamed png_set_quantize() to
 reflect more accurately what it actually does.  At the same time,
 the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
 PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
@@ -4579,12 +4721,13 @@ XI.  Changes to Libpng from version 1.4.x to 1.5.x
 
 From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
 function) incorrectly returned a value of type png_uint_32.
+The incorrect macro was removed from libpng-1.4.5.
 
-Checking for invalid palette index on read or write was added at libpng
+Checking for invalid palette index on write was added at libpng
-1.5.10.  When an invalid index is found, libpng issues a benign error.
+1.5.10.  If a pixel contains an invalid (out-of-range) index libpng issues
-This is enabled by default because this condition is an error according
+a benign error.  This is enabled by default because this condition is an
-to the PNG specification, Clause 11.3.2, but the error can be ignored in
+error according to the PNG specification, Clause 11.3.2, but the error can
-each png_ptr with
+be ignored in each png_ptr with
 
    png_set_check_for_invalid_index(png_ptr, allowed);
 
@@ -4683,7 +4826,10 @@ and the accuracy of PNG fixed point values is insufficient for
 representation of these values. Consequently a "string" API
 (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
 arbitrary sCAL chunks in the absence of either the floating point API or
-internal floating point calculations.
+internal floating point calculations.  Starting with libpng-1.5.0, both
+of these functions are present when PNG_sCAL_SUPPORTED is defined.  Prior
+to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
+being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
 
 Applications no longer need to include the optional distribution header
 file pngusr.h or define the corresponding macros during application
@@ -4703,15 +4849,10 @@ reset by pngusr.h or by explicit settings on the compiler command line.
 These settings may produce compiler warnings or errors in 1.5.0 because
 of macro redefinition.
 
-From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
-function) incorrectly returned a value of type png_uint_32.  libpng 1.5.0
-is consistent with the implementation in 1.4.5 and 1.2.x (where the macro
-did not exist.)
-
 Applications can now choose whether to use these macros or to call the
 corresponding function by defining PNG_USE_READ_MACROS or
 PNG_NO_USE_READ_MACROS before including png.h.  Notice that this is
-only supported from 1.5.0 -defining PNG_NO_USE_READ_MACROS prior to 1.5.0
+only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
 will lead to a link failure.
 
 Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
@@ -4725,7 +4866,10 @@ option was off by default, and slightly inaccurate scaling occurred.
 This option can no longer be turned off, and the choice of accurate
 or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
 API for accurate scaling or the old png_set_strip_16_to_8() API for simple
-chopping.
+chopping.  In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
+macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
+png_set_*_16_to_8() functions separately.
 
 Prior to libpng-1.5.4, the png_set_user_limits() function could only be
 used to reduce the width and height limits from the value of
@@ -4747,57 +4891,8 @@ limits are now
    png_user_chunk_cache_max  0 (unlimited)   128
    png_user_chunk_malloc_max 0 (unlimited) 8,000,000
 
-B. Changes to the build and configuration of libpng
+The png_set_option() function (and the "options" member of the png struct) was
-
+added to libpng-1.5.15.
-Details of internal changes to the library code can be found in the CHANGES
-file and in the GIT repository logs.  These will be of no concern to the vast
-majority of library users or builders; however, the few who configure libpng
-to a non-default feature set may need to change how this is done.
-
-There should be no need for library builders to alter build scripts if
-these use the distributed build support - configure or the makefiles -
-however, users of the makefiles may care to update their build scripts
-to build pnglibconf.h where the corresponding makefile does not do so.
-
-Building libpng with a non-default configuration has changed completely.
-The old method using pngusr.h should still work correctly even though the
-way pngusr.h is used in the build has been changed; however, library
-builders will probably want to examine the changes to take advantage of
-new capabilities and to simplify their build system.
-
-B.1 Specific changes to library configuration capabilities
-
-The library now supports a complete fixed point implementation and can
-thus be used on systems that have no floating point support or very
-limited or slow support.  Previously gamma correction, an essential part
-of complete PNG support, required reasonably fast floating point.
-
-As part of this the choice of internal implementation has been made
-independent of the choice of fixed versus floating point APIs and all the
-missing fixed point APIs have been implemented.
-
-The exact mechanism used to control attributes of API functions has
-changed.  A single set of operating system independent macro definitions
-is used and operating system specific directives are defined in
-pnglibconf.h
-
-As part of this the mechanism used to choose procedure call standards on
-those systems that allow a choice has been changed.  At present this only
-affects certain Microsoft (DOS, Windows) and IBM (OS/2) operating systems
-running on Intel processors.  As before, PNGAPI is defined where required
-to control the exported API functions; however, two new macros, PNGCBAPI
-and PNGCAPI, are used instead for callback functions (PNGCBAPI) and
-(PNGCAPI) for functions that must match a C library prototype (currently
-only png_longjmp_ptr, which must match the C longjmp function.)  The new
-approach is documented in pngconf.h
-
-Despite these changes, libpng 1.5.0 only supports the native C function
-calling standard on those platforms tested so far (__cdecl on Microsoft
-Windows).  This is because the support requirements for alternative
-calling conventions seem to no longer exist.  Developers who find it
-necessary to set PNG_API_RULE to 1 should advise the mailing list
-(png-mng-implement) of this and library builders who use Openwatcom and
-therefore set PNG_API_RULE to 2 should also contact the mailing list.
 
 A new test program, pngvalid, is provided in addition to pngtest.
 pngvalid validates the arithmetic accuracy of the gamma correction
@@ -4873,46 +4968,6 @@ even though the default is to use the macros - this allows applications
 to choose at app buildtime whether or not to use macros (previously
 impossible because the functions weren't in the default build.)
 
-B.2 Changes to the configuration mechanism
-
-Prior to libpng-1.5.0 library builders who needed to configure libpng
-had either to modify the exported pngconf.h header file to add system
-specific configuration or had to write feature selection macros into
-pngusr.h and cause this to be included into pngconf.h by defining
-PNG_USER_CONFIG. The latter mechanism had the disadvantage that an
-application built without PNG_USER_CONFIG defined would see the
-unmodified, default, libpng API and thus would probably fail to link.
-
-These mechanisms still work in the configure build and in any makefile
-build that builds pnglibconf.h, although the feature selection macros
-have changed somewhat as described above.  In 1.5.0, however, pngusr.h is
-processed only once, when the exported header file pnglibconf.h is built.
-pngconf.h no longer includes pngusr.h, therefore pngusr.h is ignored after the
-build of pnglibconf.h and it is never included in an application build.
-
-The rarely used alternative of adding a list of feature macros to the
-CFLAGS setting in the build also still works; however, the macros will be
-copied to pnglibconf.h and this may produce macro redefinition warnings
-when the individual C files are compiled.
-
-All configuration now only works if pnglibconf.h is built from
-scripts/pnglibconf.dfa.  This requires the program awk.  Brian Kernighan
-(the original author of awk) maintains C source code of that awk and this
-and all known later implementations (often called by subtly different
-names - nawk and gawk for example) are adequate to build pnglibconf.h.
-The Sun Microsystems (now Oracle) program 'awk' is an earlier version
-and does not work; this may also apply to other systems that have a
-functioning awk called 'nawk'.
-
-Configuration options are now documented in scripts/pnglibconf.dfa.  This
-file also includes dependency information that ensures a configuration is
-consistent; that is, if a feature is switched off dependent features are
-also removed.  As a recommended alternative to using feature macros in
-pngusr.h a system builder may also define equivalent options in pngusr.dfa
-(or, indeed, any file) and add that to the configuration by setting
-DFA_XTRA to the file name.  The makefiles in contrib/pngminim illustrate
-how to do this, and a case where pngusr.h is still required.
-
 XII.  Changes to Libpng from version 1.5.x to 1.6.x
 
 A "simplified API" has been added (see documentation in png.h and a simple
@@ -4940,20 +4995,19 @@ symbols, using the PNG_PREFIX macro.
 
 We no longer include string.h in png.h.  The include statement has been moved
 to pngpriv.h, where it is not accessible by applications.  Applications that
-need access to information in string.h must add an '#include "string.h"'
+need access to information in string.h must add an '#include <string.h>'
 directive.  It does not matter whether this is placed prior to or after
-the '"#include png.h"' directive.
+the '#include "png.h"' directive.
 
 The following API are now DEPRECATED:
    png_info_init_3()
    png_convert_to_rfc1123() which has been replaced
      with png_convert_to_rfc1123_buffer()
-   png_data_freer()
    png_malloc_default()
    png_free_default()
    png_reset_zstream()
 
-The following has been removed:
+The following have been removed:
    png_get_io_chunk_name(), which has been replaced
      with png_get_io_chunk_type().  The new
      function returns a 32-bit integer instead of
@@ -4970,8 +5024,25 @@ where "rp" indicates a "restricted pointer".
 
 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 rejected, in particular the
+profiles that were previously accepted are now accepted with a warning or
-very old broken Microsoft/HP sRGB profile.
+rejected, depending upon the png_set_benign_errors() setting, in particular the
+very old broken Microsoft/HP 3144-byte sRGB profile.  The PNG spec requirement
+that only grayscale profiles may appear in images with color type 0 or 4 and
+that even if the image only contains gray pixels, only RGB profiles may appear
+in images with color type 2, 3, or 6, is now enforced.  The sRGB chunk
+is allowed to appear in images with any color type.
+
+Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
+an empty language field or an empty translated keyword.  Both of these
+are allowed by the PNG specification, so these warnings are no longer issued.
+
+The library now issues an error if the application attempts to set a
+transform after it calls png_read_update_info() or if it attempts to call
+both png_read_update_info() and png_start_read_image() or to call either
+of them more than once.
+
+The default condition for benign_errors is now to treat benign errors as
+warnings while reading and as errors while writing.
 
 The library now issues a warning if both background processing and RGB to
 gray are used when gamma correction happens. As with previous versions of
@@ -4989,6 +5060,26 @@ The machine-generated configure files are no longer included in branches
 libpng16 and later of the GIT repository.  They continue to be included
 in the tarball releases, however.
 
+Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
+stream to set the size of the sliding window for reading instead of using the
+default 32-kbyte sliding window size.  It was discovered that there are
+hundreds of PNG files in the wild that have incorrect CMF bytes that caused
+libpng to issue a "too far back" error and reject the file.  Libpng-1.6.3 and
+later calculate their own safe CMF from the image dimensions, provide a way
+to revert to the libpng-1.5.x behavior (ignoring the CMF bytes and using a
+32-kbyte sliding window), by using
+
+    png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
+        PNG_OPTION_ON);
+
+and provide a tool (contrib/tools/pngfix) for optimizing the CMF bytes
+correctly.
+
+Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
+length, which resulted in PNG files that cannot be read beyond the bad iTXt
+chunk.  This error was fixed in libpng-1.6.3, and a tool (called
+contrib/tools/png-fix-itxt) has been added to the libpng distribution.
+
 XIII.  Detecting libpng
 
 The png_get_io_ptr() function has been present since libpng-0.88, has never
@@ -5005,11 +5096,11 @@ control.  The git repository was built from old libpng-x.y.z.tar.gz files
 going back to version 0.70.  You can access the git repository (read only)
 at
 
-    git://libpng.git.sourceforge.net/gitroot/libpng
+    git://git.code.sf.net/p/libpng/code
 
-or you can browse it via "gitweb" at
+or you can browse it with a web browser by selecting the "code" button at
 
-    http://libpng.git.sourceforge.net/git/gitweb.cgi?p=libpng
+    https://sourceforge.net/projects/libpng
 
 Patches can be sent to glennrp at users.sourceforge.net or to
 png-mng-implement at lists.sourceforge.net or you can upload them to
@@ -5087,6 +5178,9 @@ exported functions are marked with PNGAPI:
     body;
  }
 
+The return type and decorations are placed on a separate line
+ahead of the function name, as illustrated above.
+
 The prototypes for all exported functions appear in png.h,
 above the comment that says
 
@@ -5134,7 +5228,8 @@ left parenthesis that follows it:
        y[i] = a(x) + (int)b;
 
 We prefer #ifdef and #ifndef to #if defined() and #if !defined()
-when there is only one macro being tested.
+when there is only one macro being tested.  We always use parentheses
+with "defined".
 
 We prefer to express integers that are used as bit masks in hex format,
 with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
@@ -5142,6 +5237,9 @@ with an even number of lower-case hex digits (e.g., 0x00, 0xff, 0x0100).
 We prefer to use underscores in variable names rather than camelCase, except
 for a few type names that we inherit from zlib.h.
 
+We prefer "if (something != 0)" and "if (something == 0)"
+over "if (something)" and if "(!something)", respectively.
+
 We do not use the TAB character for indentation in the C sources.
 
 Lines do not exceed 80 characters.
@@ -5150,13 +5248,13 @@ Other rules can be inferred by inspecting the libpng source.
 
 XVI. Y2K Compliance in libpng
 
-February 16, 2013
+March 17, 2014
 
 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 1.6.1beta01 are Y2K compliant.  It is my belief that earlier
+upward through 1.6.11beta01 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