libjpeg-turbo是一个效率很高的图片处理的C库，所以严格来说放在Go这里不太妥当，但是之后我们会把它封装成Go可以调用的类库。据说libjpeg-turbo在处理jpeg格式图片时比ImageMagick库效率高了三倍，参照示例代码写了一个缩略图的功能：
1 // 2 // main.cpp 3 // libjpegturbo 4 // 5 // Created by 张皓然 on 2018/4/17. 6 // Copyright © 2018年 张皓然. All rights reserved. 7 // 8 9 #include <iostream> 10 #include "/opt/libjpeg-turbo/include/jpeglib.h" 11 12 using namespace std; 13 14 int compress_JPEG_file(string strImageName, string strDstImageName, int quality, int scale_num, int scale_denom) { 15 //创建必要变量，后缀in是源图片信息，out是目标图片信息，buffer是缓冲区 16 struct jpeg_decompress_struct cinfo_in; 17 struct jpeg_compress_struct cinfo_out; 18 struct jpeg_error_mgr jerr_in, jerr_out; 19 FILE *infile, *outfile; 20 JSAMPARRAY buffer; 21 //表示每行的宽度，为width*components 22 int row_stride; 23 24 //初始化对象 25 jpeg_create_decompress(&cinfo_in); 26 jpeg_create_compress(&cinfo_out); 27 //绑定错误结构 28 cinfo_in.err = jpeg_std_error(&jerr_in); 29 cinfo_out.err = jpeg_std_error(&jerr_out); 30 //C库方式打开图片文件，并填入cinfo对象 31 if((infile = fopen(strImageName.c_str(), "rb")) == NULL) { 32 fprintf(stderr, "can't open %s ", strImageName.c_str()); 33 return -1; 34 } 35 if((outfile = fopen(strDstImageName.c_str(), "wb")) == NULL) { 36 fprintf(stderr, "can't open %s ", strDstImageName.c_str()); 37 return -1; 38 } 39 jpeg_stdio_src(&cinfo_in, infile); 40 jpeg_stdio_dest(&cinfo_out, outfile); 41 //读取文件信息 42 jpeg_read_header(&cinfo_in, TRUE); 43 44 //设定文件压缩比例，M/N 45 cinfo_in.scale_num = scale_num; 46 cinfo_in.scale_denom = scale_denom; 47 48 //开始解压缩 49 jpeg_start_decompress(&cinfo_in); 50 51 //将压缩后的信息存入cinfo_out中作为新图片的参数 52 cinfo_out.image_height = cinfo_in.output_height; 53 cinfo_out.image_width = cinfo_in.output_width; 54 cinfo_out.input_components = 3; 55 cinfo_out.in_color_space = JCS_RGB; 56 jpeg_set_defaults(&cinfo_out); 57 //设置图片质量 58 jpeg_set_quality(&cinfo_out, quality, TRUE); 59 //开始压缩 60 jpeg_start_compress(&cinfo_out, TRUE); 61 62 //设定每行的宽度准备写入，并分配缓冲区空间 63 row_stride = cinfo_in.output_width * cinfo_in.output_components; 64 buffer = (*cinfo_in.mem -> alloc_sarray)((j_common_ptr)&cinfo_in, JPOOL_IMAGE, row_stride, 1); 65 66 while(cinfo_in.output_scanline < cinfo_in.output_height) { 67 //从in中读取数据并写入out中 68 jpeg_read_scanlines(&cinfo_in, buffer, 1); 69 jpeg_write_scanlines(&cinfo_out, buffer, 1); 70 } 71 72 //结束，释放变量 73 jpeg_finish_decompress(&cinfo_in); 74 jpeg_destroy_decompress(&cinfo_in); 75 76 jpeg_finish_compress(&cinfo_out); 77 jpeg_destroy_compress(&cinfo_out); 78 79 fclose(infile); 80 fclose(outfile); 81 82 return 0; 83 } 84 85 int main() { 86 clock_t start, finish; 87 start = clock(); 88 for(int i = 0; i < 100; i ++) compress_JPEG_file("/Users/zhanghaoran/Desktop/abc.jpg", "/Users/zhanghaoran/Desktop/abc_compress.jpg", 80, 1, 2); 89 finish = clock(); 90 cout << "Total : " << (double)(finish - start) / CLOCKS_PER_SEC << endl; 91 }