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The functions png_read_init(info_ptr), png_write_init(info_ptr),
png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
have been removed.  They have been deprecated since libpng-0.95.

The png_permit_empty_plte() was removed. It has been deprecated
since libpng-1.0.9.  Use png_permit_mng_features() instead.

We removed the obsolete stub functions png_get_mmx_flagmask(),
png_set_mmx_thresholds(), png_get_asm_flags(),
png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
png_set_asm_flags(), and png_mmx_supported()

We removed the obsolete png_check_sig(), png_memcpy_check(), and
png_memset_check() functions.  Instead use !png_sig_cmp(), memcpy(),
and memset(), respectively.

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.

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