libjpeg学习4：libjpeg

int tjpeg2yuv(unsigned char* jpeg_buffer, int jpeg_size, unsigned char** yuv_buffer, int* yuv_size, int* yuv_type)
{
    tjhandle handle = NULL;
    int width, height, subsample, colorspace;
    int flags = 0;
    int padding = 1; // 1或4均可，但不能是0
    int ret = 0;
 
    handle = tjInitDecompress();
    tjDecompressHeader3(handle, jpeg_buffer, jpeg_size, &width, &height, &subsample, &colorspace);
 
    printf("w: %d h: %d subsample: %d color: %d\n", width, height, subsample, colorspace);
    
    flags |= 0;
    
    *yuv_type = subsample;
    // 注：经测试，指定的yuv采样格式只对YUV缓冲区大小有影响，实际上还是按JPEG本身的YUV格式来转换的
    *yuv_size = tjBufSizeYUV2(width, padding, height, subsample);
    *yuv_buffer =(unsigned char *)malloc(*yuv_size);
    if (*yuv_buffer == NULL)
    {
        printf("malloc buffer for rgb failed.\n");
        return -1;
    }
 
    ret = tjDecompressToYUV2(handle, jpeg_buffer, jpeg_size, *yuv_buffer, width,
            padding, height, flags);
    if (ret < 0)
    {
        printf("compress to jpeg failed: %s\n", tjGetErrorStr());
    }
    tjDestroy(handle);
 
    return ret;
}
 
int tyuv2jpeg(unsigned char* yuv_buffer, int yuv_size, int width, int height, int subsample, unsigned char** jpeg_buffer, unsigned long* jpeg_size, int quality)
{
    tjhandle handle = NULL;
    int flags = 0;
    int padding = 1; // 1或4均可，但不能是0
    int need_size = 0;
    int ret = 0;
 
    handle = tjInitCompress();
   
    flags |= 0;
 
    need_size = tjBufSizeYUV2(width, padding, height, subsample);
    if (need_size != yuv_size)
    {
        printf("we detect yuv size: %d, but you give: %d, check again.\n", need_size, yuv_size);
        return 0;
    }
 
    ret = tjCompressFromYUV(handle, yuv_buffer, width, padding, height, subsample, jpeg_buffer, jpeg_size, quality, flags);
    if (ret < 0)
    {
        printf("compress to jpeg failed: %s\n", tjGetErrorStr());
    }
 
    tjDestroy(handle);
 
    return ret;
}