encode RGB24 to jpeg, using libjpeg_rgb24 生成jpeg-优快云博客

本文链接：https://blog.youkuaiyun.com/carlsonlee_freec/article/details/6233785

这段代码展示了如何使用libjpeg库将RGB24格式的图像数据编码并保存为JPEG文件。它定义了一个名为`encode_jpeg_file`的函数，接受图像文件名和质量参数，通过设置JPEG压缩结构、打开文件、设置图像属性、设置质量、开始压缩、写入扫描线并完成压缩来实现这一过程。

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#include <stdio.h>
#include "jpeglib.h"
#include <setjmp.h>

extern JSAMPLE * image_buffer;   /* Points to large array of R,G,B-order data */
extern int image_height;   /* Number of rows in image */
extern int image_width;       /* Number of columns in image */

void encode_jpeg_file (char * filename, int quality)
{
struct jpeg_compress_struct cinfo;
struct jpeg_error_mgr jerr;
FILE * outfile;       /* target file */
JSAMPROW row_pointer[1];   /* pointer to JSAMPLE row[s] */
int row_stride;       /* physical row width in image buffer */
cinfo.err = jpeg_std_error(&jerr);
jpeg_create_compress(&cinfo);

if ((outfile = fopen(filename, "wb")) == NULL) {
    fprintf(stderr, "can't open %s/n", filename);
    exit(1);
}
jpeg_stdio_dest(&cinfo, outfile);

cinfo.image_width = image_width;
cinfo.image_height = image_height;
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;

jpeg_set_defaults(&cinfo);

jpeg_set_quality(&cinfo, quality, TRUE );

jpeg_start_compress(&cinfo, TRUE);

row_stride = image_width * 3;

while (cinfo.next_scanline < cinfo.image_height)
{
    /* jpeg_write_scanlines expects an array of pointers to scanlines.
     * Here the array is only one element long, but you could pass
     * more than one scanline at a time if that's more convenient.
     */
    row_pointer[0] = & image_buffer[cinfo.next_scanline * row_stride];
    (void) jpeg_write_scanlines(&cinfo, row_pointer, 1);
}
jpeg_finish_compress(&cinfo);
fclose(outfile);
jpeg_destroy_compress(&cinfo);
}