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PNG: The Definitive Guide
Source Code
Chapters 13, 14 and 15 of "PNG: The Definitive Guide" discuss three free,
cross-platform demo programs that show how to use the libpng reference
library: rpng, rpng2 and wpng. rpng and rpng2 are viewers; the first is
a very simple example that that shows how a standard file-viewer might use
libpng, while the second is designed to process streaming data and shows
how a web browser might be written. wpng is a simple command-line program
that reads binary PGM and PPM files (the ``raw'' grayscale and RGB subsets
of PBMPLUS/NetPBM) and converts them to PNG.
The source code for all three demo programs currently compiles under
Unix, OpenVMS, and 32-bit Windows. (Special thanks to Martin Zinser,
zinser at, for making the necessary changes for OpenVMS and for
providing an appropriate build script.) Build instructions can be found
README this file
LICENSE terms of distribution and reuse (BSD-like or GNU GPL)
COPYING GNU General Public License (GPL)
Makefile.unx Unix makefile
Makefile.w32 Windows (MSVC) makefile OpenVMS build script
rpng-win.c Windows front end for the basic viewer
rpng-x.c X Window System (Unix, OpenVMS) front end
readpng.c generic back end for the basic viewer
readpng.h header file for the basic viewer
rpng2-win.c Windows front end for the progressive viewer
rpng2-x.c X front end for the progressive viewer
readpng2.c generic back end for the progressive viewer
readpng2.h header file for the progressive viewer
wpng.c generic (text) front end for the converter
writepng.c generic back end for the converter
writepng.h header file for the converter
toucan.png transparent PNG for testing (by Stefan Schneider)
Note that, although the programs are designed to be functional, their
primary purpose is to illustrate how to use libpng to add PNG support to
other programs. As such, their user interfaces are crude and definitely
are not intended for everyday use.
Please see for further infor-
mation and links to the latest version of the source code, and Chapters
13-15 of the book for detailed discussion of the three programs.
Greg Roelofs
16 March 2008
- Prerequisites (in order of compilation):
- zlib
- libpng
- pngbook
The pngbook demo programs are explicitly designed to demonstrate proper
coding techniques for using the libpng reference library. As a result,
you need to download and build both zlib (on which libpng depends) and
libpng. A common build setup is to place the zlib, libpng and pngbook
subdirectory trees ("folders") in the same parent directory. Then the
libpng build can refer to files in ../zlib (or ..\zlib or [-.zlib]),
and similarly for the pngbook build.
Note that all three packages are designed to be built from a command
line by default; those who wish to use a graphical or other integrated
development environments are on their own.
- Unix:
Unpack the latest pngbook sources (which should correspond to this
README file) into a directory and change into that directory.
Copy Makefile.unx to Makefile and edit the PNG* and Z* variables
appropriately (possibly also the X* variables if necessary).
There is no "install" target, so copy the three executables somewhere
in your path or run them from the current directory. All three will
print a basic usage screen when run without any command-line arguments;
see the book for more details.
- Windows:
Unpack the latest pngbook sources (which should correspond to this
README file) into a folder, open a "DOS shell" or "command prompt"
or equivalent command-line window, and cd into the folder where you
unpacked the source code.
For MSVC, set up the necessary environment variables by invoking
where where %devstudio% is the installation directory for MSVC /
DevStudio. If you get "environment out of space" errors under 95/98,
create a desktop shortcut with "c:\windows\ /e:4096" as
the program command line and set the working directory to the pngbook
directory. Then double-click to open the new DOS-prompt window with
a bigger environment and retry the commands above.
Copy Makefile.w32 to Makefile and edit the PNGPATH and ZPATH variables
appropriately (possibly also the "INC" and "LIB" variables if needed).
Note that the names of the dynamic and static libpng and zlib libraries
used in the makefile may change in later releases of the libraries.
Also note that, as of libpng version 1.0.5, MSVC DLL builds do not work.
This makefile therefore builds statically linked executables, but if
the DLL problems ever get fixed, uncommenting the appropriate PNGLIB
and ZLIB lines will build dynamically linked executables instead.
Do the build by typing
The result should be three executables: rpng-win.exe, rpng2-win.exe,
and wpng.exe. Copy them somewhere in your PATH or run them from the
current folder. Like the Unix versions, the two windowed programs
(rpng and rpng2) now display a usage screen in a console window when
invoked without command-line arguments; this is new behavior as of
the June 2001 release. Note that the programs use the Unix-style "-"
character to specify options, instead of the more common DOS/Windows
"/" character. (For example: "rpng2-win -bgpat 4 foo.png", not
"rpng2-win /bgpat 4 foo.png")
- OpenVMS:
Unpack the pngbook sources into a subdirectory and change into that
Edit appropriately, specifically the zpath and pngpath
To run the programs, they probably first need to be set up as "foreign
symbols," with "disk" and "dir" set appropriately:
$ rpng == "$disk:[dir]rpng-x.exe"
$ rpng2 == "$disk:[dir]rpng2-x.exe"
$ wpng == "$disk:[dir]wpng.exe"
All three will print a basic usage screen when run without any command-
line arguments; see the book for more details. Note that the options
style is Unix-like, i.e., preceded by "-" rather than "/".
rpng is a simple PNG viewer that can display transparent PNGs with a
specified background color; for example,
rpng -bgcolor \#ff0000 toucan.png
would display the image with a red background. rpng2 is a progressive
viewer that simulates a web browser in some respects; it can display
images against either a background color or a dynamically generated
background image. For example:
rpng2 -bgpat 16 toucan.png
wpng is a purely command-line image converter from binary PBMPLUS/NetPBM
format (.pgm or .ppm) to PNG; for example,
wpng -time < toucan-notrans.ppm > toucan-notrans.png
would convert the specified PPM file (using redirection) to PNG, auto-
matically setting the PNG modification-time chunk.
All options can be abbreviated to the shortest unique value; for example,
"-bgc" for -bgcolor (versus "-bgp" for -bgpat), or "-g" for -gamma.