Go初接触之libjpeg-turbo

Posted 2020-10-31 Torrance_ZHANG

　　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\n", strImageName.c_str());
33         return -1;
34     }
35     if((outfile = fopen(strDstImageName.c_str(), "wb")) == NULL) {
36         fprintf(stderr, "can‘t open %s\n", 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 }