libpng.txt - A description on how to use and modify libpng
libpng version 1.2.1 - December 12, 2001
Updated and distributed by Glenn Randers-Pehrson
<randeg@alum.rpi.edu>
Copyright (c) 1998-2001 Glenn Randers-Pehrson
For conditions of distribution and use, see copyright
notice in png.h.
based on:
libpng 1.0 beta 6 version 0.96 May 28, 1997
Updated and distributed by Andreas Dilger
Copyright (c) 1996, 1997 Andreas Dilger
libpng 1.0 beta 2 - version 0.88 January 26, 1996
For conditions of distribution and use, see copyright
notice in png.h. Copyright (c) 1995, 1996 Guy Eric
Schalnat, Group 42, Inc.
Updated/rewritten per request in the libpng FAQ
Copyright (c) 1995, 1996 Frank J. T. Wojcik
December 18, 1995 & January 20, 1996
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
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.
Libpng was written as a companion to the PNG specification, as a way
of reducing the amount of time and effort it takes to support the PNG
file format in application programs.
The PNG-1.2 specification is available at <http://www.libpng.org/pub/png>
and at <ftp://ftp.uu.net/graphics/png/documents/>.
The PNG-1.0 specification is available
as RFC 2083 <ftp://ftp.uu.net/graphics/png/documents/> and as a
W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
additional chunks are described in the special-purpose public chunks
documents at <ftp://ftp.uu.net/graphics/png/documents/>.
Other information
about PNG, and the latest version of libpng, can be found at the PNG home
page, <http://www.libpng.org/pub/png/>
and at <ftp://ftp.uu.net/graphics/png/>.
Most users will not have to modify the library significantly; advanced
users may want to modify it more. All attempts were made to make it as
complete as possible, while keeping the code easy to understand.
Currently, this library only supports C. Support for other languages
is being considered.
Libpng has been designed to handle multiple sessions at one time,
to be easily modifiable, to be portable to the vast majority of
machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
to use. The ultimate goal of libpng is to promote the acceptance of
the PNG file format in whatever way possible. While there is still
work to be done (see the TODO file), libpng should cover the
majority of the needs of its users.
Libpng uses zlib for its compression and decompression of PNG files.
Further information about zlib, and the latest version of zlib, can
be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
The zlib compression utility is a general purpose utility that is
useful for more than PNG files, and can be used without libpng.
See the documentation delivered with zlib for more details.
You can usually find the source files for the zlib utility wherever you
find the libpng source files.
Libpng is thread safe, provided the threads are using different
instances of the structures. Each thread should have its own
png_struct and png_info instances, and thus its own image.
Libpng does not protect itself against two threads using the
same instance of a structure. Note: thread safety may be defeated
by use of some of the MMX assembler code in pnggccrd.c, which is only
compiled when the user defines PNG_THREAD_UNSAFE_OK.
II. Structures
There are two main structures that are important to libpng, png_struct
and png_info. The first, png_struct, is an internal structure that
will not, for the most part, be used by a user except as the first
variable passed to every libpng function call.
The png_info structure is designed to provide information about the
PNG file. At one time, the fields of png_info were intended to be
directly accessible to the user. However, this tended to cause problems
with applications using dynamically loaded libraries, and as a result
a set of interface functions for png_info (the png_get_*() and png_set_*()
functions) was developed. The fields of png_info are still available for
older applications, but it is suggested that applications use the new
interfaces if at all possible.
Applications that do make direct access to the members of png_struct (except
for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
and applications that make direct access to the members of png_info must
be recompiled if they were compiled or loaded with libpng version 1.0.6,
in which the members were in a different order. In version 1.0.7, the
members of the png_info structure reverted to the old order, as they were
in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
structures are going to be hidden, and the contents of the structures will
only be accessible through the png_get/png_set functions.
The png.h header file is an invaluable reference for programming with libpng.
And while I'm on the topic, make sure you include the libpng header file:
#include <png.h>
III. Reading
We'll now walk you through the possible functions to call when reading
in a PNG file sequentially, briefly explaining the syntax and purpose
of each one. See example.c and png.h for more detail. While
progressive reading is covered in the next section, you will still
need some of the functions discussed in this section to read a PNG
file.
Setup
You will want to do the I/O initialization(*) before you get into libpng,
so if it doesn't work, you don't have much to undo. Of course, you
will also want to insure that you are, in fact, dealing with a PNG
file. Libpng provides a simple check to see if a file is a PNG file.
To use it, pass in the first 1 to 8 bytes of the file to the function
png_sig_cmp(), and it will return 0 if the bytes match the corresponding
bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
you pass in, the greater the accuracy of the prediction.
If you are intending to keep the file pointer open for use in libpng,
you must ensure you don't read more than 8 bytes from the beginning
of the file, and you also have to make a call to png_set_sig_bytes_read()
with the number of bytes you read from the beginning. Libpng will
then only check the bytes (if any) that your program didn't read.
(*): If you are not using the standard I/O functions, you will need
to replace them with custom functions. See the discussion under
Customizing libpng.
FILE *fp = fopen(file_name, "rb");
if (!fp)
{
return (ERROR);
}
fread(header, 1, number, fp);
is_png = !png_sig_cmp(header, 0, number);
if (!is_png)
{
return (NOT_PNG);
}
Next, png_struct and png_info need to be allocated and initialized. In
order to ensure that the size of these structures is correct even with a
dynamically linked libpng, there are functions to initialize and
allocate the structures. We also pass the library version, optional
pointers to error handling functions, and a pointer to a data struct for
use by the error functions, if necessary (the pointer and functions can
be NULL if the default error handlers are to be used). See the section
on Changes to Libpng below regarding the old initialization functions.
The structure allocation functions quietly return NULL if they fail to
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,
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图像处理VC程序\图象读取,特效,显示封装库FLib1.1及DEMO源代码 更新版 (384个子文件)
ANNOUNCE 1KB
p-21.bmp 389KB
p-43.bmp 355KB
stmp19.bmp 64KB
stmp17.bmp 64KB
stmp02.bmp 64KB
stmp28.bmp 64KB
stmp11.bmp 64KB
stmp27.bmp 64KB
stmp23.bmp 64KB
stmp25.bmp 64KB
stmp22.bmp 64KB
stmp09.bmp 64KB
stmp08.bmp 64KB
stmp16.bmp 64KB
stmp26.bmp 64KB
stmp14.bmp 64KB
stmp29.bmp 64KB
stmp12.bmp 64KB
stmp07.bmp 64KB
stmp18.bmp 64KB
stmp15.bmp 64KB
stmp10.bmp 64KB
stmp20.bmp 64KB
stmp24.bmp 64KB
stmp13.bmp 64KB
stmp21.bmp 64KB
burst.bmp 53KB
heart.bmp 53KB
stmp04.bmp 42KB
stmp03.bmp 42KB
stmp01.bmp 42KB
panel_disable.bmp 10KB
panel_enable.bmp 10KB
toolbar_disable.bmp 9KB
toolbar_enable.bmp 9KB
panel.bmp 5KB
Toolbar.bmp 4KB
CHART.BMP 2KB
pnggccrd.c 233KB
pngvcrd.c 143KB
pngrtran.c 141KB
pngrutil.c 88KB
pngwutil.c 82KB
tif_ojpeg.c 81KB
fax3sm_winnt.c 79KB
tif_getimage.c 64KB
DEFLATE.C 49KB
JQUANT2.C 49KB
pngwrite.c 47KB
pngtest.c 46KB
pngread.c 45KB
TREES.C 44KB
pngpread.c 43KB
tif_fax3.c 42KB
JDMARKER.C 41KB
JMEMMGR.C 41KB
tif_jpeg.c 41KB
tif_luv.c 39KB
tif_dirread.c 38KB
tif_dir.c 36KB
tif_pixarlog.c 35KB
pngset.c 33KB
JQUANT1.C 31KB
tif_dirwrite.c 30KB
example.c 30KB
JCHUFF.C 28KB
tif_lzw.c 27KB
GZIO.C 26KB
pngget.c 26KB
JCPHUFF.C 25KB
JDCOEFCT.C 25KB
png.c 23KB
JCPARAM.C 21KB
Jdhuff.c 21KB
JDPHUFF.C 21KB
JDMAINCT.C 20KB
pngtrans.c 20KB
JCMASTER.C 20KB
JDMASTER.C 20KB
tif_write.c 20KB
JCSAMPLE.C 19KB
tif_read.c 18KB
JCMARKER.C 17KB
pngwtran.c 17KB
JDSAMPLE.C 16KB
JCCOEFCT.C 16KB
tif_print.c 16KB
INFTREES.C 16KB
EXAMPLE.C 16KB
tif_dirinfo.c 16KB
JCCOLOR.C 15KB
JIDCTINT.C 15KB
pngmem.c 14KB
JCTRANS.C 14KB
JDMERGE.C 14KB
JIDCTRED.C 14KB
JDINPUT.C 14KB
JIDCTFST.C 13KB
tif_open.c 13KB
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