linux c 缩放 api

#include <stdio.h>
#include <stdlib.h>
#include <jpeglib.h>

void scale_jpeg(const char *input_filename, const char *output_filename, int new_width, int new_height) {
    FILE *infile, *outfile;
    struct jpeg_decompress_struct srcinfo;
    struct jpeg_compress_struct dstinfo;
    struct jpeg_error_mgr jsrcerr, jdsterr;
    JSAMPARRAY buffer;
    int row_stride;

    // 打开源文件
    if ((infile = fopen(input_filename, "rb")) == NULL) {
        fprintf(stderr, "Can't open %s\n", input_filename);
        return;
    }

    // 初始化JPEG解压缩对象
    srcinfo.err = jpeg_std_error(&jsrcerr);
    jpeg_create_decompress(&srcinfo);
    jpeg_stdio_src(&srcinfo, infile);
    jpeg_read_header(&srcinfo, TRUE);

    // 设置新的尺寸
    jpeg_calc_output_dimensions(&srcinfo, new_width, new_height);

    // 创建目标文件
    if ((outfile = fopen(output_filename, "wb")) == NULL) {
        fprintf(stderr, "Can't open %s\n", output_filename);
        return;
    }

    // 初始化JPEG压缩对象
    dstinfo.err = jpeg_std_error(&jdsterr);
    jpeg_create_compress(&dstinfo);
    jpeg_stdio_dest(&dstinfo, outfile);

    // 设置压缩参数
    dstinfo.image_width = new_width;
    dstinfo.image_height = new_height;
    dstinfo.input_components = srcinfo.output_components;
    dstinfo.in_color_space = srcinfo.out_color_space;
    jpeg_set_defaults(&dstinfo);

    // 开始压缩
    jpeg_start_compress(&dstinfo, TRUE);

    // 分配内存并读取源图像数据
    buffer = (*srcinfo.mem->alloc_sarray)((j_common_ptr) &srcinfo, JPOOL_IMAGE, row_stride = srcinfo.output_width * srcinfo.output_components, 1);

    // 缩放并写入目标文件
    while (srcinfo.output_scanline < srcinfo.output_height) {
        jpeg_read_scanlines(&srcinfo, buffer, 1);
        // 这里可以添加缩放算法，例如双线性插值
        jpeg_write_scanlines(&dstinfo, buffer, 1);
    }

    // 完成压缩并释放资源
    jpeg_finish_compress(&dstinfo);
    jpeg_destroy_compress(&dstinfo);
    jpeg_finish_decompress(&srcinfo);
    jpeg_destroy_decompress(&srcinfo);

    fclose(infile);
    fclose(outfile);
}

int main() {
    scale_jpeg("input.jpg", "output.jpg", 800, 600);
    return 0;
}