库安装就不说了，我是直接下载编译好的库

Independent JPEG Group (ijg.org)

这个需要自己编译

可以使用的代码

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

void compress_jpeg(const char* input_filename, const char* output_filename, int quality) {
    struct jpeg_decompress_struct cinfo_in;
    struct jpeg_compress_struct cinfo_out;
    struct jpeg_error_mgr jerr_in, jerr_out;

    FILE* input_file = NULL;
    errno_t err1 = fopen_s(&input_file, input_filename, "rb");
    if (err1) {
        fprintf(stderr, "Error opening input file.\n");
        exit(1);
    }

    FILE* output_file = NULL;
    errno_t err2 = fopen_s(&output_file, output_filename, "wb");
    if (err2) {
        fprintf(stderr, "Error opening output file.\n");
        exit(1);
    }


    if (!input_file || !output_file) {
        fprintf(stderr, "Error opening files.\n");
        exit(1);
    }

    // Decompress
    cinfo_in.err = jpeg_std_error(&jerr_in);
    jpeg_create_decompress(&cinfo_in);
    jpeg_stdio_src(&cinfo_in, input_file);
    jpeg_read_header(&cinfo_in, TRUE);
    jpeg_start_decompress(&cinfo_in);

    JSAMPLE* buffer = (JSAMPLE*)malloc(cinfo_in.output_width * cinfo_in.output_components);

    // Compress
    cinfo_out.err = jpeg_std_error(&jerr_out);
    jpeg_create_compress(&cinfo_out);
    jpeg_stdio_dest(&cinfo_out, output_file);
    cinfo_out.image_width = cinfo_in.image_width;
    cinfo_out.image_height = cinfo_in.image_height;
    cinfo_out.input_components = cinfo_in.num_components;
    cinfo_out.in_color_space = cinfo_in.out_color_space;

    jpeg_set_defaults(&cinfo_out);
    jpeg_set_quality(&cinfo_out, quality, TRUE);
    jpeg_start_compress(&cinfo_out, TRUE);

    while (cinfo_in.output_scanline < cinfo_in.output_height) {
        jpeg_read_scanlines(&cinfo_in, &buffer, 1);
        jpeg_write_scanlines(&cinfo_out, &buffer, 1);
    }

    jpeg_finish_decompress(&cinfo_in);
    jpeg_finish_compress(&cinfo_out);

    jpeg_destroy_decompress(&cinfo_in);
    jpeg_destroy_compress(&cinfo_out);

    free(buffer);
    fclose(input_file);
    fclose(output_file);
}

int main() {
    const char* input = R"(C:\Users\Administrator\Desktop\ThreeData\weixingOBJ\tex\Tile_+000_+000_23_00013300_0000.jpg)";
    const char* output = R"(C:\Users\Administrator\Desktop\ThreeData\weixingOBJ\tex\outlibjpeg.jpg)";
    compress_jpeg(input, output, 50);  // 50 is the quality, it can be from 0 to 100.

    printf("Compression done. Check %s\n", output);
    return 0;
}

顺便把这个库集成到OSG库中