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[devel] Updated manual synopses, fixed several typos,

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put paramter descriptions in proper order, applied libpng indentation
style in code snippets.
This commit is contained in:
Glenn Randers-Pehrson 2011-01-21 23:29:09 -06:00
parent b86b4928d6
commit 7bc25013f0
2 changed files with 626 additions and 260 deletions
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255
libpng-manual.txt
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@ -1,6 +1,6 @@
libpng-manual.txt - A description on how to use and modify libpng
libpng version 1.5.1rc01 - January 21, 2011
libpng version 1.5.1beta07 - January 22, 2011
Updated and distributed by Glenn Randers-Pehrson
<glennrp at users.sourceforge.net>
Copyright (c) 1998-2011 Glenn Randers-Pehrson
@ -11,7 +11,7 @@ libpng-manual.txt - A description on how to use and modify libpng
Based on:
libpng versions 0.97, January 1998, through 1.5.1rc01 - January 21, 2011
libpng versions 0.97, January 1998, through 1.5.1beta07 - January 22, 2011
Updated and distributed by Glenn Randers-Pehrson
Copyright (c) 1998-2011 Glenn Randers-Pehrson
@ -311,8 +311,10 @@ Customizing libpng.
{
return (ERROR);
}
fread(header, 1, number, fp);
is_png = !png_sig_cmp(header, 0, number);
if (!is_png)
{
return (NOT_PNG);
@ -333,10 +335,12 @@ create the structure, so your application should check for that.
png_structp png_ptr = png_create_read_struct
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
png_destroy_read_struct(&png_ptr,
@ -345,6 +349,7 @@ create the structure, so your application should check for that.
}
png_infop end_info = png_create_info_struct(png_ptr);
if (!end_info)
{
png_destroy_read_struct(&png_ptr, &info_ptr,
@ -353,7 +358,7 @@ create the structure, so your application should check for that.
}
If you want to use your own memory allocation routines,
define PNG_USER_MEM_SUPPORTED and use
use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
png_create_read_struct_2() instead of png_create_read_struct():
png_structp png_ptr = png_create_read_struct_2
@ -523,14 +528,17 @@ chunk types. To change this, you can call:
1: ignore; do not keep
2: keep only if safe-to-copy
3: keep even if unsafe-to-copy
You can use these definitions:
PNG_HANDLE_CHUNK_AS_DEFAULT 0
PNG_HANDLE_CHUNK_NEVER 1
PNG_HANDLE_CHUNK_IF_SAFE 2
PNG_HANDLE_CHUNK_ALWAYS 3
chunk_list - list of chunks affected (a byte string,
five bytes per chunk, NULL or '\0' if
num_chunks is 0)
num_chunks - number of chunks affected; if 0, all
unknown chunks are affected. If nonzero,
only the chunks in the list are affected
@ -566,8 +574,10 @@ callback function:
#if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
/* ignore all unknown chunks: */
png_set_keep_unknown_chunks(read_ptr, 1, 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);
@ -681,16 +691,21 @@ row_pointers prior to calling png_read_png() with
if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
png_error (png_ptr,
"Image is too tall to process in memory");
if (width > PNG_UINT_32_MAX/pixel_size)
png_error (png_ptr,
"Image is too wide to process in memory");
row_pointers = png_malloc(png_ptr,
height*png_sizeof(png_bytep));
for (int i=0; i<height, i++)
row_pointers[i]=NULL; /* security precaution */
for (int i=0; i<height, i++)
row_pointers[i]=png_malloc(png_ptr,
width*pixel_size);
png_set_rows(png_ptr, info_ptr, &row_pointers);
Alternatively you could allocate your image in one big block and define
@ -700,7 +715,7 @@ If you use png_set_rows(), the application is responsible for freeing
row_pointers (and row_pointers[i], if they were separately allocated).
If you don't allocate row_pointers ahead of time, png_read_png() will
do it, and it'll be free'ed when you call png_destroy_*().
do it, and it'll be free'ed by libpng when you call png_destroy_*().
The low-level read interface
@ -724,13 +739,16 @@ in until png_read_end() has read the chunk data following the image.
width - holds the width of the image
in pixels (up to 2^31).
height - holds the height of the image
in pixels (up to 2^31).
bit_depth - holds the bit depth of one of the
image channels. (valid values are
1, 2, 4, 8, 16 and depend also on
the color_type. See also
significant bits (sBIT) below).
color_type - describes which color/alpha channels
are present.
PNG_COLOR_TYPE_GRAY
@ -773,28 +791,38 @@ in until png_read_end() has read the chunk data following the image.
width = png_get_image_width(png_ptr,
info_ptr);
height = png_get_image_height(png_ptr,
info_ptr);
bit_depth = png_get_bit_depth(png_ptr,
info_ptr);
color_type = png_get_color_type(png_ptr,
info_ptr);
interlace_type = png_get_interlace_type(png_ptr,
info_ptr);
compression_type = png_get_compression_type(png_ptr,
info_ptr);
filter_method = png_get_filter_type(png_ptr,
info_ptr);
channels = png_get_channels(png_ptr, info_ptr);
channels - number of channels of info for the
color type (valid values are 1 (GRAY,
PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
4 (RGB_ALPHA or RGB + filler byte))
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
rowbytes - number of bytes needed to hold a row
signature = png_get_signature(png_ptr, info_ptr);
signature - holds the signature read from the
file (if any). The data is kept in
the same offset it would be if the
@ -814,15 +842,19 @@ pointer into the info_ptr is returned for any complex types.
png_get_PLTE(png_ptr, info_ptr, &palette,
&num_palette);
palette - the palette for the file
(array of png_color)
num_palette - number of entries in the palette
png_get_gAMA(png_ptr, info_ptr, &gamma);
gamma - the gamma the file is written
at (PNG_INFO_gAMA)
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
srgb_intent - the rendering intent (PNG_INFO_sRGB)
The presence of the sRGB chunk
means that the pixel data is in the
@ -832,16 +864,21 @@ pointer into the info_ptr is returned for any complex types.
png_get_iCCP(png_ptr, info_ptr, &name,
&compression_type, &profile, &proflen);
name - The profile name.
compression_type - The compression type; always
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
You may give NULL to this argument to
ignore it.
profile - International Color Consortium color
profile data. May contain NULs.
proflen - length of profile data in bytes.
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
sig_bit - the number of significant bits for
(PNG_INFO_sBIT) each of the gray,
red, green, and blue channels,
@ -850,50 +887,66 @@ pointer into the info_ptr is returned for any complex types.
png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
&num_trans, &trans_color);
trans_alpha - array of alpha (transparency)
entries for palette (PNG_INFO_tRNS)
num_trans - number of transparent entries
(PNG_INFO_tRNS)
trans_color - graylevel or color sample values of
the single transparent color for
non-paletted images (PNG_INFO_tRNS)
png_get_hIST(png_ptr, info_ptr, &hist);
(PNG_INFO_hIST)
hist - histogram of palette (array of
png_uint_16)
png_get_tIME(png_ptr, info_ptr, &mod_time);
mod_time - time image was last modified
(PNG_VALID_tIME)
png_get_bKGD(png_ptr, info_ptr, &background);
background - background color (PNG_VALID_bKGD)
valid 16-bit red, green and blue
values, regardless of color_type
num_comments = png_get_text(png_ptr, info_ptr,
&text_ptr, &num_text);
num_comments - number of comments
text_ptr - array of png_text holding image
comments
text_ptr[i].compression - type of compression used
on "text" PNG_TEXT_COMPRESSION_NONE
PNG_TEXT_COMPRESSION_zTXt
PNG_ITXT_COMPRESSION_NONE
PNG_ITXT_COMPRESSION_zTXt
text_ptr[i].key - keyword for comment. Must contain
1-79 characters.
text_ptr[i].text - text comments for current
keyword. Can be empty.
text_ptr[i].text_length - length of text string,
after decompression, 0 for iTXt
text_ptr[i].itxt_length - length of itxt string,
after decompression, 0 for tEXt/zTXt
text_ptr[i].lang - language of comment (empty
string for unknown).
text_ptr[i].lang_key - keyword in UTF-8
(empty string for unknown).
Note that the itxt_length, lang, and lang_key
members of the text_ptr structure only exist
when the library is built with iTXt chunk support.
@ -901,6 +954,7 @@ pointer into the info_ptr is returned for any complex types.
num_text - number of comments (same as
num_comments; you can put NULL here
to avoid the duplication)
Note while png_set_text() will accept text, language,
and translated keywords that can be NULL pointers, the
structure returned by png_get_text will always contain
@ -909,49 +963,68 @@ pointer into the info_ptr is returned for any complex types.
num_spalettes = png_get_sPLT(png_ptr, info_ptr,
&palette_ptr);
num_spalettes - number of sPLT chunks read.
palette_ptr - array of palette structures holding
contents of one or more sPLT chunks
read.
num_spalettes - number of sPLT chunks read.
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
&unit_type);
offset_x - positive offset from the left edge
of the screen
offset_y - positive offset from the top edge
of the screen
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
&unit_type);
res_x - pixels/unit physical resolution in
x direction
res_y - pixels/unit physical resolution in
x direction
unit_type - PNG_RESOLUTION_UNKNOWN,
PNG_RESOLUTION_METER
png_get_sCAL(png_ptr, info_ptr, &unit, &width,
&height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units
(width and height are doubles)
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
&height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units
(width and height are strings like "2.54")
num_unknown_chunks = png_get_unknown_chunks(png_ptr,
info_ptr, &unknowns)
unknowns - array of png_unknown_chunk
structures holding unknown chunks
unknowns[i].name - name of unknown chunk
unknowns[i].data - data of unknown chunk
unknowns[i].size - size of unknown chunk's data
unknowns[i].location - position of chunk in file
The value of "i" corresponds to the order in which the
@ -963,34 +1036,55 @@ forms:
res_x = png_get_x_pixels_per_meter(png_ptr,
info_ptr)
res_y = png_get_y_pixels_per_meter(png_ptr,
info_ptr)
res_x_and_y = png_get_pixels_per_meter(png_ptr,
info_ptr)
res_x = png_get_x_pixels_per_inch(png_ptr,
info_ptr)
res_y = png_get_y_pixels_per_inch(png_ptr,
info_ptr)
res_x_and_y = png_get_pixels_per_inch(png_ptr,
info_ptr)
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
info_ptr)
(Each of these returns 0 [signifying "unknown"] if
Each of these returns 0 [signifying "unknown"] if
the data is not present or if res_x is 0;
res_x_and_y is 0 if res_x != res_y)
res_x_and_y is 0 if res_x != res_y
Note that because of the way the resolutions are
stored internally, the inch conversions won't
come out to exactly even number. For example,
72 dpi is stored as 0.28346 pixels/meter, and
when this is retrieved it is 71.9988 dpi, so
be sure to round the returned value appropriately
if you want to display a reasonable-looking result.
The data from the oFFs chunk can be retrieved in several convenient
forms:
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
(Each of these returns 0 [signifying "unknown" if both
Each of these returns 0 [signifying "unknown" if both
x and y are 0] if the data is not present or if the
chunk is present but the unit is the pixel)
chunk is present but the unit is the pixel. The
remark about inexact inch conversions applies here
as well, because a value in inches can't always be
converted to microns and back without some loss
of precision.
For more information, see the png_info definition in png.h and the
PNG specification for chunk contents. Be careful with trusting
@ -1077,7 +1171,7 @@ things.
As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
added. It expands the sample depth without changing tRNS to alpha.
As of libpng version 1.5.1rc01, not all possible expansions are supported.
As of libpng version 1.5.1beta07, not all possible expansions are supported.
In the following table, the 01 means grayscale with depth<8, 31 means
indexed with depth<8, other numerals represent the color type, "T" means
@ -1209,15 +1303,18 @@ with alpha.
int red_weight, int green_weight);
error_action = 1: silently do the conversion
error_action = 2: issue a warning if the original
image has any pixel where
red != green or red != blue
error_action = 3: issue an error and abort the
conversion if the original
image has any pixel where
red != green or red != blue
red_weight: weight of red component times 100000
green_weight: weight of green component times 100000
If either weight is negative, default
weights (21268, 71514) are used.
@ -1305,6 +1402,7 @@ a slightly smaller exponent is better.
{
screen_gamma = user_defined_screen_gamma;
}
/* One way that applications can share the same
screen gamma value */
else if ((gamma_str = getenv("SCREEN_GAMMA"))
@ -1312,13 +1410,16 @@ a slightly smaller exponent is better.
{
screen_gamma = (double)atof(gamma_str);
}
/* If we don't have another value */
else
{
screen_gamma = 2.2; /* A good guess for a
PC monitor in a bright office or a dim room */
screen_gamma = 2.0; /* A good guess for a
PC monitor in a dark room */
screen_gamma = 1.7 or 1.0; /* A good
guess for Mac systems */
}
@ -1335,6 +1436,7 @@ recommended that PNG viewers support gamma correction.
if (png_get_gAMA(png_ptr, info_ptr, &gamma))
png_set_gamma(png_ptr, screen_gamma, gamma);
else
png_set_gamma(png_ptr, screen_gamma, 0.45455);
@ -1342,7 +1444,7 @@ If you need to reduce an RGB file to a paletted file, or if a paletted
file has more entries then will fit on your screen, png_set_quantize()
will do that. Note that this is a simple match quantization that merely
finds the closest color available. This should work fairly well with
optimized palettes, and fairly badly with linear color cubes. If you
optimized palettes, but fairly badly with linear color cubes. If you
pass a palette that is larger then maximum_colors, the file will
reduce the number of colors in the palette so it will fit into
maximum_colors. If there is a histogram, it will use it to make
@ -1361,6 +1463,7 @@ histogram, it may not do as good a job.
png_set_quantize(png_ptr, palette, num_palette,
max_screen_colors, histogram, 1);
}
else
{
png_color std_color_cube[MAX_SCREEN_COLORS] =
@ -1454,13 +1557,13 @@ are allocating one large chunk, you will need to build an
array of pointers to each row, as it will be needed for some
of the functions below.
Remember: Before you call png_read_update_info the png_get_
Remember: Before you call png_read_update_info(), the png_get_
functions return the values corresponding to the original PNG image.
After you call png_read_update_info the values refer to the image
that libpng will output. Consequently you must call all the png_set_
functions before you call png_read_update_info. This is particularly
important for png_set_interlace_handling - if you are going to call
png_read_update_info you must call png_set_interlace_handling before
functions before you call png_read_update_info(). This is particularly
important for png_set_interlace_handling() - if you are going to call
png_read_update_info() you must call png_set_interlace_handling() before
it unless you want to receive interlaced output.
Reading image data
@ -1610,12 +1713,14 @@ These allow you to write the obvious loop:
while (output_x < output_image_width)
{
image[output_y][output_x] = subimage[pass][input_y][input_x++];
image[output_y][output_x] =
subimage[pass][input_y][input_x++];
output_x += xStep;
}
++input_y;
ouput_y += yStep;
output_y += yStep;
}
Notice that the steps between successive output rows and columns are
@ -1667,6 +1772,7 @@ It is also possible to individually free the info_ptr members that
point to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
mask - identifies data to be freed, a mask
containing the bitwise OR of one or
more of
@ -1676,6 +1782,7 @@ point to libpng-allocated storage with the following function:
PNG_FREE_SCAL, PNG_FREE_SPLT,
PNG_FREE_TEXT, PNG_FREE_UNKN,
or simply PNG_FREE_ALL
seq - sequence number of item to be freed
(-1 for all items)
@ -1693,13 +1800,15 @@ or so that it will free data that was allocated by the user with png_malloc()
or png_zalloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
mask - which data elements are affected
same choices as in png_free_data()
freer - one of
PNG_DESTROY_WILL_FREE_DATA
PNG_SET_WILL_FREE_DATA
PNG_USER_WILL_FREE_DATA
mask - which data elements are affected
same choices as in png_free_data()
This function only affects data that has already been allocated.
You can call this function after reading the PNG data but before calling
any png_set_*() functions, to control whether the user or the png_set_*()
@ -1728,6 +1837,7 @@ it frees. If you need to turn the flag off for a chunk that was freed by
your application instead of by libpng, you can use
png_set_invalid(png_ptr, info_ptr, mask);
mask - identifies the chunks to be made invalid,
containing the bitwise OR of one or
more of
@ -1767,13 +1877,16 @@ png_infop info_ptr;
png_ptr = png_create_read_struct
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
(png_infopp)NULL);
png_destroy_read_struct(&png_ptr,
(png_infopp)NULL, (png_infopp)NULL);
return (ERROR);
}
@ -1938,10 +2051,9 @@ using the standard I/O functions, you will need to replace them with
custom writing functions. See the discussion under Customizing libpng.
FILE *fp = fopen(file_name, "wb");
if (!fp)
{
return (ERROR);
}
Next, png_struct and png_info need to be allocated and initialized.
As these can be both relatively large, you may not want to store these
@ -1954,6 +2066,7 @@ both "png_ptr"; you can call them anything you like, such as
png_structp png_ptr = png_create_write_struct
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
user_error_fn, user_warning_fn);
if (!png_ptr)
return (ERROR);
@ -2057,7 +2170,8 @@ filter types.
/* turn on or off filtering, and/or choose
specific filters. You can use either a single
PNG_FILTER_VALUE_NAME or the bitwise OR of one
or more PNG_FILTER_NAME masks. */
or more PNG_FILTER_NAME masks.
*/
png_set_filter(png_ptr, 0,
PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
@ -2113,16 +2227,20 @@ Some of the more important parts of the png_info are:
png_set_IHDR(png_ptr, info_ptr, width, height,
bit_depth, color_type, interlace_type,
compression_type, filter_method)
width - holds the width of the image
in pixels (up to 2^31).
height - holds the height of the image
in pixels (up to 2^31).
bit_depth - holds the bit depth of one of the
image channels.
(valid values are 1, 2, 4, 8, 16
and depend also on the
color_type. See also significant
bits (sBIT) below).
color_type - describes which color/alpha
channels are present.
PNG_COLOR_TYPE_GRAY
@ -2142,8 +2260,10 @@ Some of the more important parts of the png_info are:
interlace_type - PNG_INTERLACE_NONE or
PNG_INTERLACE_ADAM7
compression_type - (must be
PNG_COMPRESSION_TYPE_DEFAULT)
filter_method - (must be PNG_FILTER_TYPE_DEFAULT
or, if you are writing a PNG to
be embedded in a MNG datastream,
@ -2161,15 +2281,18 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_PLTE(png_ptr, info_ptr, palette,
num_palette);
palette - the palette for the file
(array of png_color)
num_palette - number of entries in the palette
png_set_gAMA(png_ptr, info_ptr, gamma);
gamma - the gamma the image was created
at (PNG_INFO_gAMA)
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
srgb_intent - the rendering intent
(PNG_INFO_sRGB) The presence of
the sRGB chunk means that the pixel
@ -2189,6 +2312,7 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
srgb_intent);
srgb_intent - the rendering intent
(PNG_INFO_sRGB) The presence of the
sRGB chunk means that the pixel
@ -2200,16 +2324,21 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_iCCP(png_ptr, info_ptr, name, compression_type,
profile, proflen);
name - The profile name.
compression_type - The compression type; always
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
You may give NULL to this argument to
ignore it.
profile - International Color Consortium color
profile data. May contain NULs.
proflen - length of profile data in bytes.
png_set_sBIT(png_ptr, info_ptr, sig_bit);
sig_bit - the number of significant bits for
(PNG_INFO_sBIT) each of the gray, red,
green, and blue channels, whichever are
@ -2218,30 +2347,38 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_tRNS(png_ptr, info_ptr, trans_alpha,
num_trans, trans_color);
trans_alpha - array of alpha (transparency)
entries for palette (PNG_INFO_tRNS)
trans_color - graylevel or color sample values
(in order red, green, blue) of the
single transparent color for
non-paletted images (PNG_INFO_tRNS)
num_trans - number of transparent entries
(PNG_INFO_tRNS)
png_set_hIST(png_ptr, info_ptr, hist);
(PNG_INFO_hIST)
hist - histogram of palette (array of
png_uint_16)
png_set_tIME(png_ptr, info_ptr, mod_time);
mod_time - time image was last modified
(PNG_VALID_tIME)
png_set_bKGD(png_ptr, info_ptr, background);
background - background color (PNG_VALID_bKGD)
png_set_text(png_ptr, info_ptr, text_ptr, num_text);
text_ptr - array of png_text holding image
comments
text_ptr[i].compression - type of compression used
on "text" PNG_TEXT_COMPRESSION_NONE
PNG_TEXT_COMPRESSION_zTXt
@ -2267,6 +2404,7 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
num_spalettes);
palette_ptr - array of png_sPLT_struct structures
to be added to the list of palettes
in the info structure.
@ -2275,35 +2413,48 @@ width, height, bit_depth, and color_type must be the same in each call.
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
unit_type);
offset_x - positive offset from the left
edge of the screen
offset_y - positive offset from the top
edge of the screen
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
unit_type);
res_x - pixels/unit physical resolution
in x direction
res_y - pixels/unit physical resolution
in y direction
unit_type - PNG_RESOLUTION_UNKNOWN,
PNG_RESOLUTION_METER
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units
(width and height are doubles)
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
unit - physical scale units (an integer)
width - width of a pixel in physical scale units
height - height of a pixel in physical scale units
(width and height are strings like "2.54")
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
num_unknowns)
unknowns - array of png_unknown_chunk
structures holding unknown chunks
unknowns[i].name - name of unknown chunk
@ -2342,21 +2493,30 @@ Until text gets around 1000 bytes, it is not worth compressing it.
After the text has been written out to the file, the compression type
is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
so that it isn't written out again at the end (in case you are calling
png_write_end() with the same struct.
png_write_end() with the same struct).
The keywords that are given in the PNG Specification are:
Title Short (one line) title or
caption for image
Author Name of image's creator
Description Description of image (possibly long)
Copyright Copyright notice
Creation Time Time of original image creation
(usually RFC 1123 format, see below)
Software Software used to create the image
Disclaimer Legal disclaimer
Warning Warning of nature of content
Source Device used to create the image
Comment Miscellaneous comment; conversion
from other image format
@ -2530,10 +2690,12 @@ file so that decoders can recover the original data if desired.
sig_bit.green = true_bit_depth;
sig_bit.blue = true_bit_depth;
}
else
{
sig_bit.gray = true_bit_depth;
}
if (color_type & PNG_COLOR_MASK_ALPHA)
{
sig_bit.alpha = true_bit_depth;
@ -2719,6 +2881,7 @@ It is also possible to individually free the info_ptr members that
point to libpng-allocated storage with the following function:
png_free_data(png_ptr, info_ptr, mask, seq)
mask - identifies data to be freed, a mask
containing the bitwise OR of one or
more of
@ -2728,6 +2891,7 @@ point to libpng-allocated storage with the following function:
PNG_FREE_SCAL, PNG_FREE_SPLT,
PNG_FREE_TEXT, PNG_FREE_UNKN,
or simply PNG_FREE_ALL
seq - sequence number of item to be freed
(-1 for all items)
@ -2749,19 +2913,22 @@ or so that it will free data that was allocated by the user with png_malloc()
or png_zalloc() and passed in via a png_set_*() function, with
png_data_freer(png_ptr, info_ptr, freer, mask)
mask - which data elements are affected
same choices as in png_free_data()
freer - one of
PNG_DESTROY_WILL_FREE_DATA
PNG_SET_WILL_FREE_DATA
PNG_USER_WILL_FREE_DATA
mask - which data elements are affected
same choices as in png_free_data()
For example, to transfer responsibility for some data from a read structure
to a write structure, you could use
png_data_freer(read_ptr, read_info_ptr,
PNG_USER_WILL_FREE_DATA,
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
png_data_freer(write_ptr, write_info_ptr,
PNG_DESTROY_WILL_FREE_DATA,
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
@ -2827,6 +2994,7 @@ Your replacement memory functions must have prototypes as follows:
png_voidp malloc_fn(png_structp png_ptr,
png_alloc_size_t size);
void free_fn(png_structp png_ptr, png_voidp ptr);
Your malloc_fn() must return NULL in case of failure. The png_malloc()
@ -2859,8 +3027,10 @@ The replacement I/O functions must have prototypes as follows:
void user_read_data(png_structp png_ptr,
png_bytep data, png_size_t length);
void user_write_data(png_structp png_ptr,
png_bytep data, png_size_t length);
void user_flush_data(png_structp png_ptr);
The user_read_data() function is responsible for detecting and
@ -2905,6 +3075,7 @@ parameters as follows:
void user_error_fn(png_structp png_ptr,
png_const_charp error_msg);
void user_warning_fn(png_structp png_ptr,
png_const_charp warning_msg);
@ -3015,8 +3186,10 @@ zlib.h for more information on what these mean.
png_set_compression_strategy(png_ptr,
strategy);
png_set_compression_window_bits(png_ptr,
window_bits);
png_set_compression_method(png_ptr, method);
png_set_compression_buffer_size(png_ptr, size);
@ -3106,6 +3279,8 @@ 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,
@ -3180,11 +3355,13 @@ Libpng can support some of these extensions. To enable them, use the
png_permit_mng_features() function:
feature_set = png_permit_mng_features(png_ptr, mask)
mask is a png_uint_32 containing the bitwise OR of the
features you want to enable. These include
PNG_FLAG_MNG_EMPTY_PLTE
PNG_FLAG_MNG_FILTER_64
PNG_ALL_MNG_FEATURES
feature_set is a png_uint_32 that is the bitwise AND of
your mask with the set of MNG features that is
supported by the version of libpng that you are using.
@ -3209,7 +3386,7 @@ still alive and well, but they have moved on to other things.
The old libpng functions png_read_init(), png_write_init(),
png_info_init(), png_read_destroy(), and png_write_destroy() have been
moved to PNG_INTERNAL in version 0.95 to discourage their use. These
functions will be removed from libpng version 2.0.0.
functions will be removed from libpng version 1.4.0.
The preferred method of creating and initializing the libpng structures is
via the png_create_read_struct(), png_create_write_struct(), and
@ -3445,7 +3622,8 @@ PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
was reenabled, 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.
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.
@ -3472,7 +3650,7 @@ png_memcmp(), png_sprintf, and png_memcpy() 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_bytepp.
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
@ -3587,8 +3765,8 @@ 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 chose procedure call standards on those
systems that allow a choice has been changed. At present this only
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
@ -3689,8 +3867,8 @@ 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 once when the exported header file pnglibconf.h is built.
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 it is ignored after the
build of pnglibconf.h and it is never included in an application build.
@ -3745,6 +3923,11 @@ the libpng bug tracker at
http://libpng.sourceforge.net
We also accept patches built from the tar or zip distributions, and
simple verbal discriptions of bug fixes, reported either to the
SourceForge bug tracker or to the png-mng-implement at lists.sf.net
mailing list.
XIII. Coding style
Our coding style is similar to the "Allman" style, with curly
@ -3855,13 +4038,13 @@ Other rules can be inferred by inspecting the libpng source.
XIV. Y2K Compliance in libpng
January 21, 2011
January 22, 2011
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 1.5.1rc01 are Y2K compliant. It is my belief that earlier
upward through 1.5.1beta07 are Y2K compliant. It is my belief that earlier
versions were also Y2K compliant.
Libpng only has three year fields. One is a 2-byte unsigned integer that

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