【C++】图像加载（libpng、FreeImage、stb |
您所在的位置：网站首页 › 蓝色的饮料怎么调 › 【C++】图像加载（libpng、FreeImage、stb |
|
图像加载
目录 图像加载 一、前言 二、对比 三、stb_image 四、FreeImage 五、libpng 一、前言libpng、FreeImage、stb_image都是图像解析的开源库，由于三者我都简单使用过，于是做个总结对比。 二、对比 库开源协议编译依赖win编译难度使用难度格式支持libpngzlibzlib自带vs工程中只支持pngFreeImage混合自带了7、8个库有dll发行版简单很多stb_imageMIT无只有头文件简单常用的几个它们的官网如下： libpng Home Page The FreeImage Project GitHub - nothings/stb: stb single-file public domain libraries for C/C++ 总的来说，它们的开源协议都问题不大。源码编译stb_image最简单，因为它只有一个头文件。而libpng是操作png文件的库，代码比较复杂，但是它的优点是灵活，速度更快。FreeImage集成了各种加载库，支持的格式比较多。 接下来，我就按使用难度给出它们的基本代码。注意均是读取到uint32_t缓冲区，代表RGBA32位颜色，如下： class Image { //other uint32_t* _data; array _size; }注意我并没有处理字节序问题，是写死的，在不同大小端的系统运行，应该改进一下代码（我懒得很，要等到遇到问题再解决，就是交换一下单个像素RGBA通道的读取顺序）。 觉得有用，请点赞、收藏、关注。我写这篇文件就是因为有人get了我以前写的libpng的文章。 三、stb_image读取如下，确实很简单，直接返回的就是RGBA32位颜色： #define STB_IMAGE_IMPLEMENTATION #include dnd::Image* Image::Create(string_view path_name) { int texWidth, texHeight, texChannels; stbi_uc* pixels = stbi_load(string{ path_name }.c_str(), &texWidth, &texHeight, &texChannels, STBI_rgb_alpha); if (!pixels) { debug_err(format("加载图像失败：{}", path_name)); return nullptr; } Image* ret = new Image; ret->_data = (uint32_t*)pixels; ret->_size = { (unsigned)texWidth, (unsigned)texHeight }; return ret; }导出图像数据更简单; #define STB_IMAGE_WRITE_IMPLEMENTATION #include bool Image::SaveToFile(string_view path_name) { return stbi_write_png(string{ path_name }.c_str(), _size[0], _size[1], 4, _data, 0); }注意，我们应该使用它的释放函数来释放资源，转回stbi_uc*类型（实际上也就是调用了free函数，不过大家都懂不要自己free）： stbi_image_free((stbi_uc*)_data); 四、FreeImage代码中用到的一些函数（语法糖）如下： /** * @brief RAII清理操作 */ template class finally { public: finally(F&& func) : _func(func) {} ~finally() { _func(); } private: F _func; }; //! 对容器任意元素的判断 namespace Any { /** * @brief 判断容器任意元素等于某值 * @param[in] container 操作的容器 * @param[in] v 要比较的值 */ template bool Equal(const C& container, const V& v) { for (auto& iter : container) { if (iter == v) return true; } return false; } }读取代码如下： #include string path_name_mb = String::cvt_u8_mb(path_name); const char* filename = path_name_mb.c_str(); //读文件头判断格式 FREE_IMAGE_FORMAT file_format = FreeImage_GetFileType(filename, 0); if (file_format == FIF_UNKNOWN) {//通过文件名读取 file_format = FreeImage_GetFIFFromFilename(filename); } if (file_format == FIF_UNKNOWN) { debug_err("图像文件格式不支持：" + string{ path_name }); return nullptr; } //格式支持读取则读取 FIBITMAP* bitmap = nullptr; if (FreeImage_FIFSupportsReading(file_format)) { bitmap = FreeImage_Load(file_format, filename); } if (!bitmap) { return nullptr; } //资源释放 finally f0([&]() { FreeImage_Unload(bitmap); }); // unsigned bpp = FreeImage_GetBPP(bitmap); //取像素深度 FREE_IMAGE_TYPE file_type = FreeImage_GetImageType(bitmap); //取数据类型 BYTE* bits = FreeImage_GetBits(bitmap); //取像素数组 unsigned w = FreeImage_GetWidth(bitmap); //宽 unsigned h = FreeImage_GetHeight(bitmap); //高 unsigned pitch = FreeImage_GetPitch(bitmap); //每行像素(freeimage自动做了32位对齐, gl默认也是32位对齐) if (bits == 0 || w == 0 || h == 0) { debug_err("图像文件基本数据错误：" + string{ path_name }); return nullptr; } // if (file_type != FIT_BITMAP) { debug_err("图像文件类型不是位图：" + string{ path_name }); return nullptr; } // vector mul_bpp{ 32, 24, 8 }; if (!Any::Equal(mul_bpp, bpp)) { debug_err(format("图像文件不支持的色深({})：", bpp, path_name)); return nullptr; } // Image* ret = new Image; ret->_size = { w, h }; size_t length = size_t(w * h); ret->_buffer = new uint32[length]; //BGRA => ABGR（RGBA） 单个访问时有字节序问题，需要反过来 if (bpp == 32) { for (unsigned x = 0; x < w; ++x) { for (unsigned y = 0; y < h; ++y) { unsigned p0 = y * w + x; unsigned p1 = (h - 1 - y) * pitch + x * 4; char* p = (char*)&(ret->_buffer[p0]); p[0] = bits[p1 + 2]; p[1] = bits[p1 + 1]; p[2] = bits[p1 + 0]; p[3] = bits[p1 + 3]; } } } else if (bpp == 24) { for (unsigned x = 0; x < w; x++) { for (unsigned y = 0; y < h; y++) { unsigned p0 = y * w + x; unsigned p1 = (h - 1 - y) * pitch + x * 3; char* p = (char*)&(ret->_buffer[p0]); p[0] = bits[p1 + 2]; p[1] = bits[p1 + 1]; p[2] = bits[p1 + 0]; p[3] = (char)255; } } } else if (bpp == 8) { for (unsigned x = 0; x < w; x++) { for (unsigned y = 0; y < h; y++) { unsigned p0 = y * w + x; unsigned p1 = (h - 1 - y) * pitch + x * 1; char* p = (char*)&(ret->_buffer[p0]); p[0] = bits[p1]; p[1] = bits[p1]; p[2] = bits[p1]; p[3] = (char)255; } } } return ret;导出图像数据到文件： string path_name_mb = String::cvt_u8_mb(path_name); const char* filename = path_name_mb.c_str(); FREE_IMAGE_FORMAT file_format = FreeImage_GetFIFFromFilename(filename); if (file_format == FIF_UNKNOWN) { debug_err("不支持的图像格式：" + string{ path_name }); return false; } unsigned w = _size[0]; unsigned h = _size[1]; uint32_t* bits = new uint32_t[w * h]; //ABGR（RGBA）=> BGRA 单个访问时有字节序问题，需要反过来 for (unsigned x = 0; x < w; ++x) { for (unsigned y = 0; y < h; ++y) { unsigned index = y * w + x; char* p_dst = (char*)&(bits[index]); char* p = (char*)&(_buffer[index]); p_dst[0] = p[2]; p_dst[1] = p[1]; p_dst[2] = p[0]; p_dst[3] = p[3]; } } // FIBITMAP* bitmap = FreeImage_ConvertFromRawBits((BYTE*)bits, w, h, w * 4, 32, 0, 0, 0, true); delete[] bits; FreeImage_Save(file_format, bitmap, filename); //释放 FreeImage_Unload(bitmap); return true; 五、libpng这里的代码比较陈旧，用了win32的类型，自行修改一下即可。加载代码如下： #include Image* img = new Image; ///从文件加载/ FILE* fp = NULL; if (sys->GetFile(path, fp) == -1) { debug_err(String(L"DND: Image::Create: 图像文件打开失败: ") + path); return NULL; } //判断是否问 png 文件 size_t number = 8; png_bytep header = new png_byte[number]; fread(header, 1, number, fp); bool is_png = !png_sig_cmp(header, 0, number); if (!is_png) { fclose(fp); debug_err(String(L"DND: Image::Create: 必须是png文件: ") + path); return NULL; } //初始化pnglib png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); if (!png_ptr) { fclose(fp); debug_err(L"DND: Image::Create: 初始化pnglib失败！"); return NULL; } //创建图像信息 info png_infop info_ptr = png_create_info_struct(png_ptr); if (!info_ptr) { fclose(fp); debug_err(L"DND: Image::Create: 创建png_info失败！"); return NULL; } //错误处理 if (setjmp(png_jmpbuf(png_ptr))) { fclose(fp); png_destroy_read_struct(&png_ptr, &info_ptr, NULL); debug_err(L"DND: Image::Create: pnglib出现错误！"); return NULL; } //设置数据源 png_init_io(png_ptr, fp); //表明文件头已处理 png_set_sig_bytes(png_ptr, number); //读png 这一步会实际分配内存 png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0); fclose(fp); //从info查询数据 unsigned w = png_get_image_width(png_ptr, info_ptr); //获得图片宽度 unsigned h = png_get_image_height(png_ptr, info_ptr); //获得图片高度 int color_type = png_get_color_type(png_ptr, info_ptr); //获得图片颜色类型 //赋值image img->_size.w = w; img->_size.h = h; img->_buffer = new DWORD[w*h]; //从info 复制到 image png_bytep *row_point = NULL; row_point = png_get_rows(png_ptr, info_ptr); int block_size = (color_type == 6 ? 4 : 3); //(A)RGB unsigned pos = 0; for (unsigned x = 0; x < h; ++x) for (unsigned y = 0; y < w*block_size; y += block_size) { ((unsigned char*)img->_buffer)[pos + 0] = row_point[x][y + 2];//b; ((unsigned char*)img->_buffer)[pos + 1] = row_point[x][y + 1];//g ((unsigned char*)img->_buffer)[pos + 2] = row_point[x][y + 0];//r if (color_type == 6) ((unsigned char*)img->_buffer)[pos + 3] = row_point[x][y + 3];//a else ((unsigned char*)img->_buffer)[pos + 3] = 0xff; pos += 4; } //释放png内存 png_destroy_read_struct(&png_ptr, &info_ptr, NULL); return img;导出图像数据到文件： FILE* fp; png_infop info_ptr; char cpath[MAX_PATH] = { NULL }; path.GetMultiByteStr(cpath, MAX_PATH); fopen_s(&fp, cpath, "wb"); if (fp == NULL) { debug_err(L"DND: Image::SaveToPNG: 创建文件失败！"); return; } //初始化pnglib static png_structp png_ptr = NULL; if (!png_ptr) png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL); if (!png_ptr) { debug_err(L"DND: Image::SaveToPNG: 创建文件时初始化pnglib失败！"); return; } info_ptr = png_create_info_struct(png_ptr); if (info_ptr == NULL) { fclose(fp); debug_err(L"DND: Image::SaveToPNG: png_create_info_struct失败！"); return; } //错误处理 if (setjmp(png_jmpbuf(png_ptr))) { fclose(fp); png_destroy_write_struct(&png_ptr, (png_infopp)NULL); debug_err(L"DND: Image::SaveToPNG: pnglib 出现错误！"); return; } unsigned bit_depth = 8; unsigned pixel_byte = 4; unsigned row_byte = _size.w * pixel_byte; //设置输出控制 png_init_io(png_ptr, fp); //设置图像属性 png_set_IHDR(png_ptr, info_ptr, _size.w, _size.h, bit_depth, PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE, //交错无 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE); //写头部 png_write_info(png_ptr, info_ptr); //获取行指针 png_bytepp row_pointers = (png_bytep*)malloc(_size.h*sizeof(png_bytep)); for (unsigned x = 0; x < _size.h; ++x) {//分配一行 row_pointers[x] = (png_bytep)malloc(row_byte); for (unsigned y = 0; y < row_byte; y += pixel_byte) { row_pointers[x][y + 2] = ((unsigned char*)_buffer)[x * row_byte + y + 0]; row_pointers[x][y + 1] = ((unsigned char*)_buffer)[x * row_byte + y + 1]; row_pointers[x][y + 0] = ((unsigned char*)_buffer)[x * row_byte + y + 2]; row_pointers[x][y + 3] = ((unsigned char*)_buffer)[x * row_byte + y + 3]; /*row_pointers[x][y + 2] = row_pointers[x][y + 1] = row_pointers[x][y + 0] = row_pointers[x][y + 3] = 0xff;*/ } } //写入全部 png_write_image(png_ptr, row_pointers); //写尾部 png_write_end(png_ptr, info_ptr); //释放png内存 png_destroy_write_struct(&png_ptr, (png_infopp) NULL); /* delete[] row_pointers; delete[] image;*/ for (unsigned x = 0; x < _size.h; ++x) {//释放每行 free(row_pointers[x]); } free(row_pointers); fclose(fp); |
今日新闻 |
推荐新闻 |
| CopyRight 2018-2019 办公设备维修网 版权所有 豫ICP备15022753号-3 |