libjpeg YUV转jpeg

要将YUV图像转换为JPEG图像，需要使用libjpeg库。下面是一个简单的示例代码：

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

#define WIDTH 640
#define HEIGHT 480

void yuv_to_rgb(unsigned char *yuv, unsigned char *rgb) {
    int y = yuv[0], u = yuv[1], v = yuv[2];
    int r = y + 1.402 * (v - 128);
    int g = y - 0.34414 * (u - 128) - 0.71414 * (v - 128);
    int b = y + 1.772 * (u - 128);
    rgb[0] = (unsigned char)r;
    rgb[1] = (unsigned char)g;
    rgb[2] = (unsigned char)b;
}

void yuv_to_jpeg(unsigned char *yuv_data, unsigned char *jpeg_data, int quality) {
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    JSAMPROW row_pointer[1];
    int row_stride;

    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);
    jpeg_mem_dest(&cinfo, &jpeg_data, &jpeg_size);

    cinfo.image_width = WIDTH;
    cinfo.image_height = 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);

    unsigned char rgb_data[WIDTH * HEIGHT * 3];
    for (int y = 0; y < HEIGHT; y++) {
        for (int x = 0; x < WIDTH; x++) {
            int i = y * WIDTH + x;
            yuv_to_rgb(yuv_data + i * 3, rgb_data + i * 3);
        }
        row_pointer[0] = &rgb_data[y * WIDTH * 3];
        row_stride = WIDTH * 3;
        jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }
    jpeg_finish_compress(&cinfo);
    jpeg_destroy_compress(&cinfo);
}

int main() {
    unsigned char yuv_data[WIDTH * HEIGHT * 3];
    // 从文件或摄像头等读取YUV数据
    unsigned char jpeg_data[WIDTH * HEIGHT * 3];
    yuv_to_jpeg(yuv_data, jpeg_data, 80);
    // 将JPEG数据写入文件或发送到网络等
    return 0;
}

该代码将YUV图像转换为RGB图像，然后使用libjpeg库将RGB图像压缩为JPEG格式。在`yuv_to_jpeg`函数中，首先创建一个`jpeg_compress_struct`结构体，并设置压缩参数。然后，将RGB图像逐行写入JPEG文件，最后完成压缩并销毁压缩结构体。