+The function png_set_gray_1_2_4_to_8() was removed. It has been
+deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
+png_set_expand_gray_1_2_4_to_8() because the former function also
+expanded any tRNS chunk to an alpha channel.
+
+Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
+were added and are used by default instead of the corresponding
+functions. Unfortunately,
+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.
+
+We changed the prototype for png_malloc() from
+ png_malloc(png_structp png_ptr, png_uint_32 size)
+to
+ png_malloc(png_structp png_ptr, png_alloc_size_t size)
+
+This also applies to the prototype for the user replacement malloc_fn().
+
+The png_calloc() function was added and is used in place of
+of "png_malloc(); memset();" except in the case in png_read_png()
+where the array consists of pointers; in this case a "for" loop is used
+after the png_malloc() to set the pointers to NULL, to give robust.
+behavior in case the application runs out of memory part-way through
+the process.
+
+We changed the prototypes of png_get_compression_buffer_size() and
+png_set_compression_buffer_size() to work with png_size_t instead of
+png_uint_32.
+
+Support for numbered error messages was removed by default, since we
+never got around to actually numbering the error messages. The function
+png_set_strip_error_numbers() was removed from the library by default.
+
+The png_zalloc() and png_zfree() functions are no longer exported.
+The png_zalloc() function no longer zeroes out the memory that it
+allocates. Applications that called png_zalloc(png_ptr, number, size)
+can call png_calloc(png_ptr, number*size) instead, and can call
+png_free() instead of png_zfree().
+
+Support for dithering was disabled by default in libpng-1.4.0, because
+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 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
+was renamed to PNG_READ_QUANTIZE_SUPPORTED.
+
+We removed the trailing '.' from the warning and error messages.
+
+.SH 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 write was added at libpng
+1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
+a benign error. This is enabled by default because this condition is an
+error according to the PNG specification, Clause 11.3.2, but the error can
+be ignored in each png_ptr with
+
+ png_set_check_for_invalid_index(png_ptr, allowed);
+
+ allowed - one of
+ 0: disable benign error (accept the
+ invalid data without warning).
+ 1: enable benign error (treat the
+ invalid data as an error or a
+ warning).
+
+If the error is ignored, or if png_benign_error() treats it as a warning,
+any invalid pixels are decoded as opaque black by the decoder and written
+as-is by the encoder.
+
+Retrieving the maximum palette index found was added at libpng-1.5.15.
+This statement must appear after png_read_png() or png_read_image() while
+reading, and after png_write_png() or png_write_image() while writing.
+
+ int max_palette = png_get_palette_max(png_ptr, info_ptr);
+
+This will return the maximum palette index found in the image, or "\-1" if
+the palette was not checked, or "0" if no palette was found. Note that this
+does not account for any palette index used by ancillary chunks such as the
+bKGD chunk; you must check those separately to determine the maximum
+palette index actually used.
+
+There are no substantial API changes between the non-deprecated parts of
+the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
+members of the main libpng control structures, png_struct and png_info,
+deprecated in earlier versions of libpng, has been completely removed from
+libpng 1.5.
+
+We no longer include zlib.h in png.h. The include statement has been moved
+to pngstruct.h, where it is not accessible by applications. Applications that
+need access to information in zlib.h will need to add the '#include "zlib.h"'
+directive. It does not matter whether this is placed prior to or after
+the '"#include png.h"' directive.
+
+The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
+and were removed.
+
+We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
+macros into a private header file (pngpriv.h) that is not accessible to
+applications.
+
+In png_get_iCCP, the type of "profile" was changed from png_charpp
+to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
+
+There are changes of form in png.h, including new and changed macros to
+declare parts of the API. Some API functions with arguments that are
+pointers to data not modified within the function have been corrected to
+declare these arguments with PNG_CONST.
+
+Much of the internal use of C macros to control the library build has also
+changed and some of this is visible in the exported header files, in
+particular the use of macros to control data and API elements visible
+during application compilation may require significant revision to
+application code. (It is extremely rare for an application to do this.)
+
+Any program that compiled against libpng 1.4 and did not use deprecated
+features or access internal library structures should compile and work
+against libpng 1.5, except for the change in the prototype for
+png_get_iCCP() and png_set_iCCP() API functions mentioned above.
+
+libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
+interlaced images. The macros return the number of rows and columns in
+each pass and information that can be used to de-interlace and (if
+absolutely necessary) interlace an image.
+
+libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
+the application-provided png_longjmp_ptr on the internal, but application
+initialized, longjmp buffer. It is provided as a convenience to avoid
+the need to use the png_jmpbuf macro, which had the unnecessary side
+effect of resetting the internal png_longjmp_ptr value.
+
+libpng 1.5.0 includes a complete fixed point API. By default this is
+present along with the corresponding floating point API. In general the
+fixed point API is faster and smaller than the floating point one because
+the PNG file format used fixed point, not floating point. This applies
+even if the library uses floating point in internal calculations. A new
+macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
+uses floating point arithmetic (the default) or fixed point arithmetic
+internally for performance critical calculations such as gamma correction.
+In some cases, the gamma calculations may produce slightly different
+results. This has changed the results in png_rgb_to_gray and in alpha
+composition (png_set_background for example). This applies even if the
+original image was already linear (gamma == 1.0) and, therefore, it is
+not necessary to linearize the image. This is because libpng has *not*
+been changed to optimize that case correctly, yet.
+
+Fixed point support for the sCAL chunk comes with an important caveat;
+the sCAL specification uses a decimal encoding of floating point values
+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. 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
+build in order to see the correct variant of the libpng API. From 1.5.0
+application code can check for the corresponding _SUPPORTED macro:
+
+#ifdef PNG_INCH_CONVERSIONS_SUPPORTED
+ /* code that uses the inch conversion APIs. */
+#endif
+
+This macro will only be defined if the inch conversion functions have been
+compiled into libpng. The full set of macros, and whether or not support
+has been compiled in, are available in the header file pnglibconf.h.
+This header file is specific to the libpng build. Notice that prior to
+1.5.0 the _SUPPORTED macros would always have the default definition unless
+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.
+
+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
+will lead to a link failure.
+
+Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
+when compressing the IDAT data and textual data such as zTXt and iCCP.
+In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
+We added five png_set_text_*() functions for setting the parameters to
+use with textual data.
+
+Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
+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. 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
+PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
+that it could be used to override them. Now this function will reduce or
+increase the limits.
+
+Starting in libpng-1.5.10, the user limits can be set en masse with the
+configuration option PNG_SAFE_LIMITS_SUPPORTED. If this option is enabled,
+a set of "safe" limits is applied in pngpriv.h. These can be overridden by
+application calls to png_set_user_limits(), png_set_user_chunk_cache_max(),
+and/or png_set_user_malloc_max() that increase or decrease the limits. Also,
+in libpng-1.5.10 the default width and height limits were increased
+from 1,000,000 to 0x7ffffff (i.e., made unlimited). Therefore, the
+limits are now
+ default safe
+ png_user_width_max 0x7fffffff 1,000,000
+ png_user_height_max 0x7fffffff 1,000,000
+ png_user_chunk_cache_max 0 (unlimited) 128
+ png_user_chunk_malloc_max 0 (unlimited) 8,000,000
+
+The png_set_option() function (and the "options" member of the png struct) was
+added to libpng-1.5.15.
+
+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, as described in the INSTALL file.
+
+A new test program, pngvalid, is provided in addition to pngtest.
+pngvalid validates the arithmetic accuracy of the gamma correction
+calculations and includes a number of validations of the file format.
+A subset of the full range of tests is run when "make check" is done
+(in the 'configure' build.) pngvalid also allows total allocated memory
+usage to be evaluated and performs additional memory overwrite validation.
+
+Many changes to individual feature macros have been made. The following
+are the changes most likely to be noticed by library builders who
+configure libpng:
+
+1) All feature macros now have consistent naming:
+
+#define PNG_NO_feature turns the feature off
+#define PNG_feature_SUPPORTED turns the feature on
+
+pnglibconf.h contains one line for each feature macro which is either:
+
+#define PNG_feature_SUPPORTED
+
+if the feature is supported or:
+
+/*#undef PNG_feature_SUPPORTED*/
+
+if it is not. Library code consistently checks for the 'SUPPORTED' macro.
+It does not, and libpng applications should not, check for the 'NO' macro
+which will not normally be defined even if the feature is not supported.
+The 'NO' macros are only used internally for setting or not setting the
+corresponding 'SUPPORTED' macros.
+
+Compatibility with the old names is provided as follows:
+
+PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
+
+And the following definitions disable the corresponding feature:
+
+PNG_SETJMP_NOT_SUPPORTED disables SETJMP
+PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
+PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
+PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
+PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
+PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
+
+Library builders should remove use of the above, inconsistent, names.
+
+2) Warning and error message formatting was previously conditional on
+the STDIO feature. The library has been changed to use the
+CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
+the library no longer uses the printf(3) functions, even though the
+default read/write implementations use (FILE) style stdio.h functions.
+
+3) Three feature macros now control the fixed/floating point decisions:
+
+PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
+
+PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
+practice these are normally required internally anyway (because the PNG
+file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
+merely stops the function from being exported.
+
+PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
+point implementation or the fixed point one. Typically the fixed point
+implementation is larger and slower than the floating point implementation
+on a system that supports floating point; however, it may be faster on a
+system which lacks floating point hardware and therefore uses a software
+emulation.
+
+4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
+functions to read and write ints to be disabled independently of
+PNG_USE_READ_MACROS, which allows libpng to be built with the functions
+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.)
+
+.SH 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
+example in contrib/examples/pngtopng.c). The new publicly visible API
+includes the following:
+
+ macros:
+ PNG_FORMAT_*
+ PNG_IMAGE_*
+ structures:
+ png_control
+ png_image
+ read functions
+ png_image_begin_read_from_file()
+ png_image_begin_read_from_stdio()
+ png_image_begin_read_from_memory()
+ png_image_finish_read()
+ png_image_free()
+ write functions
+ png_image_write_to_file()
+ png_image_write_to_stdio()
+
+Starting with libpng-1.6.0, you can configure libpng to prefix all exported
+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>'
+directive. It does not matter whether this is placed prior to or after
+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_malloc_default()
+ png_free_default()
+ png_reset_zstream()
+
+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
+ a string.
+ The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
+ png_memset() macros are no longer used in the libpng sources and
+ have been removed. These had already been made invisible to applications
+ (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
+
+The signatures of many exported functions were changed, such that
+ png_structp became png_structrp or png_const_structrp
+ png_infop became png_inforp or png_const_inforp
+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 accepted with a warning or
+rejected, depending upon the png_set_benign_errors() setting, in particular the
+very old broken Microsoft/HP 3144-byte sRGB profile. Starting with
+libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by
+means of
+
+ #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
+ defined(PNG_SET_OPTION_SUPPORTED)
+ png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE,
+ PNG_OPTION_ON);
+ #endif
+
+It's not a good idea to do this if you are using the "simplified API",
+which needs to be able to recognize an sRGB profile conveyed via the iCCP
+chunk.
+
+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
+and is interpreted by libpng to convey a one-tracer-curve gray profile or a
+three-tracer-curve RGB profile as appropriate.
+
+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
+the library the results are numerically very incorrect in this case.
+
+There are some minor arithmetic changes in some transforms such as
+png_set_background(), that might be detected by certain regression tests.
+
+Unknown chunk handling has been improved internally, without any API change.
+This adds more correct option control of the unknown handling, corrects
+a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
+it possible to skip IDAT chunks in the sequential reader.
+
+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
+zlib to issue the "invalid distance 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 rewriting a PNG file while
+optimizing the CMF bytes in its IDAT chunk 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.
+
+.SH XIII. Detecting libpng