LodePNG

LodePNG for C (ISO C90) and C++

LodePNG is a PNG image decoder and encoder, all in one, no dependency or linkage to zlib or libpng required.
It's made for C (ISO C90), and has a C++ wrapper with a more convenient interface on top.

On GitHub

See lodepng.h for documentation.

lodepng.cpp: The source file for the C++ version (and after renaming it, for the C version)
lodepng.c: Just get lodepng.cpp and rename it to lodepng.c
lodepng.h: header for both the C and C++ version.

Usage examples:

example_decode.cpp: Decoding in C++
example_decode.c: Decoding in C
example_encode.cpp: Encoding in C++
example_encode.c: Encoding in C
example_sdl.cpp: Show PNG image with SDL in C++
example_sdl.c: Show PNG image with SDL in C
example_opengl.cpp: Show PNG image with OpenGL
example_png_info.cpp: Lists lots of information about a PNG image in text form
example_4bit_palette.cpp: Generates 4-bit PNG with translucent palette
example_reencode.cpp: Decodes PNG, then reencodes it close to the original
example_optimize_png.cpp: Encodes a PNG with higher compression, but slower
example_gzip.cpp: Encode a file to a gzip file (.gz)
example_png2bmp.cpp: Convert PNG to BMP
example_bmp2png.cpp: Convert BMP to PNG

Other utilities:

lodepng_util.cpp: Utilities to extract internal information from PNGs.
lodepng_util.h: Header file for lodepng_util.cpp
pngdetail.cpp: Prints detailed info of PNG images, including filter types and huffman symbols
lodepng_unittest.cpp: Unit tests for LodePNG
lodepng_benchmark.cpp: Benchmark for LodePNG

picoPNG

There is also picoPNG, which is only the decoder part of LodePNG, wrapped in one single C++ function of around 500 lines. This is less well maintained than LodePNG, has less features, and may be less efficient.

The function, decodePNG, converts any PNG file data, with any colortype or interlace mode, into a 32-bit image in an std::vector at the output.

picopng.cpp

Other versions

http://www.dsource.org/projects/scrapple/wiki/LodePngLibrary: D programming language port by Lutger
pngread.bas, pngwrite.bas: BASIC 7.1 port by Daniel Nice

FAQ

Q: When using OpenGL and decoding textures with LodePNG, the image is upside down.

A: LodePNG uses a pixel order where it goes in rows from top to bottom. In OpenGL, how would you define upside down? There are many things which affect the orientation with which something is drawn in OpenGL: camera orientation, texture coordinates, the orientation of the object, ... If you don't want to solve the problem by changing OpenGL coordinates, e.g. because your game engine uses a bottom to top representation for all textures, you can still go through the raw pixel buffer of LodePNG with a for loop and swap the rows to become upside down. Remember that for 32-bit RGBA, each row is (width * 4 bytes) long, for 24-bit RGB it's (width * 3 bytes) long.

Q: The image is wrong when using LodePNG with BITMAPs in Visual Studio or win32, or with BMP images.

A: LodePNG uses raw buffers with RGBA or RGB pixels in the common order RGBARGBARGBA... or RGBRGBRGBRGB..., from top to bottom, without any special byte boundaries. BMP images and bitmaps in win32 use a different format. They do three things differently:

Instead of being from top to bottom, it goes from bottom to top (upside down).
Instead of using the order red, green, blue, it uses the order blue, green, red, or BGRBGRBGR..., (can result in wrong colors).
It has a limitation where rows always must be a multiple of 4 bytes, so if the width of the image is not a multiple of 4 some unused bytes are introduced at the end of each row (can result in a skewed image).

All of this are related to how BMP works, not how PNG or LodePNG work. When you're working with BMP, you need to take each of these three things into account and convert this to/from the buffer format that LodePNG uses. Also check out the png2bmp and bmp2png samples, which already do this.

Q: What's the difference between zlib, deflate and gzip? And between CRC32 and ADLER32?

A: That can be confusing. In short:

PNG uses zlib. Zlib uses deflate. Gzip uses deflate and is not used by PNG.
PNG uses CRC32, and indirectly ADLER32. Zlib uses ADLER32. Gzip uses CRC32.
IETF Standards: PNG is RFC 2083. Zlib is RFC 1950. Deflate is RFC 1951. Gzip is RFC 1952.

Q: picoPNG doesn't support some feature.

A: Try LodePNG instead. It supports more than picoPNG, and is better maintained. The code of picoPNG may be small, but its compiled executable may not be. If you want to compile to a really small executable, then LodePNG can probably do this better because it supports the C language instead of only C++, and has the ability to turn off pieces of code you don't need by changing some #defines in the header.

Q: Error 29 when loading PNG when using XCode.

A: XCode may modify PNG images to a proprietary file format not compatible with the real PNG standard. Disable a setting "Compress PNG Files" under "Packaging" to get valid PNGs.

Q: Why did the interface of LodePNG change? Why not keep it as is, fixing compile errors is annoying!

A: Sorry about that. Sometimes when a feature is added the interface grows into something inconsistent, and then I try to redesign it to get a new, better, one. And sometimes when a new feature is added the cleanest way to do it requires an interface change. In the last change, the following improvements were made that changed it:

There used to be some fields in camelCase, and others with_underscores. Now, this is made more consistent: all fields and functions use underscore between words (except between two nouns that form one word, like bitdepth or palettesize), and all typenames start with a capital and use CamelCase.
The large amount of structs got reduced a bit.
The C++ class got removed: there was really no reason to have a class here. A encoder and decoder class with subclass implementations makes sense in a framework that can encode/decode many different image formats, but not in a single format like here. Instead, a convenient RAII wrapper lodepng::State is available around the new LodePNGState struct.
The C++ namespace is lodepng instead of LodePNG because namespaces look better in small letters imho.

Change History

More detailed change history is in the header file.

2005: LodePNG created for C++, it could only decode PNGs.
2006: Many interface changes, fixes and improvements.
2007: Full PNG and Zlib encoder and compressor added.
2008: Converted all the code to C instead of C++, with a C++ wrapper around it.
2010: Small bugfixes and header and documentation restructured.
2012: Revamped interface with more consistent names, rewrote some parts, bugfixes.
2014: Moved to github, further changes not listed here.

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