LodePNG入门

标签：lodepng   png   

LodePNG是一个集合了PNG图像解码器和编码器的代码文件，不依赖于诸如zlib和libpng的外部链接/库，提供方便友好的PNG编解码器调用方法。LodePNG主要是采用C（ISO C90）编写的，并提供了C++的接口。LodePNG的使用非常简单，只要在项目文件中包含lodepng.cpp和lodepng.h或者lodepng.c和lodepng.h就可以。

LodePNG文件：

lodepng.cpp: 这个LodePNG的主体部分，里面实现了PNG的编解码的核心功能，无需多言。

lodepng.c: 如果你要在c语言下使用，只要把上面的文件重命名为lodepng.c就可以了。

lodepng.h: 是lodepng.cpp和lodepng.c的头文件。

应用例程：

• example_decode.cpp: 在C++下如何解码PNG文件。
• example_decode.c: 在C下如何解码PNG文件。
• example_encode.cpp: 在C++下如何将像素数据编码成PNG文件。
• example_encode.c: 在C下如何将像素数据编码成PNG文件。
• example_sdl.cpp: 在C++下如何利用SDL显示PNG图像。
• example_sdl.c: 在C下如何利用SDL显示PNG图像。
• example_opengl.cpp: 利用OpenGL显示PNG图像。
• example_png_info.cpp: 显示PNG的信息文件。
• 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: 如何将PNG图像转化为BMP图像。
• example_bmp2png.cpp: 如何将BMP图像转化为PNG图像。

几个常用函数：

unsigned lodepng_decode_memory(unsigned char** out, unsigned* w, unsigned* h,
                               const unsigned char* in, size_t insize,
                               LodePNGColorType colortype, unsigned bitdepth);

这个函数将一张PNG图像解码成原始的像素数据。

参数：

out:  Pointer to buffer that will contain the raw pixel data.After decoding, its size is w * h * (bytes per pixel) bytes larger than initially. Bytes per pixel depends on colortype and bitdepth.Must be freed after usage with free(*out).Note: for 16-bit per channel colors, uses big endian format like PNG does.

w:  Pointer to width of pixel data.

h: Pointer to height of pixel data.

in: Memory buffer with the PNG file.

insize: size of the in buffer.

colortype: the desired color type for the raw output image. See explanation on PNG color types.

bitdepth: the desired bit depth for the raw output image. See explanation on PNG color types.

Return value: LodePNG error code (0 means no error).

unsigned lodepng_encode_file(const char* filename,
                             const unsigned char* image, unsigned w, unsigned h,
                             LodePNGColorType colortype, unsigned bitdepth);

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: 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.

官方原文链接：http://lodev.org/lodepng/

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LodePNG入门

标签：lodepng   png   

原文地址：http://blog.csdn.net/linj_m/article/details/26457377