int main(int argc, char **argv)
{
    const string about =
        "This sample demonstrates recoloring grayscale images with dnn.\n"
        "This program is based on:\n"
        "  http://richzhang.github.io/colorization\n"
        "  https://github.com/richzhang/colorization\n"
        "Download caffemodel and prototxt files:\n"
        "  http://eecs.berkeley.edu/~rich.zhang/projects/2016_colorization/files/demo_v2/colorization_release_v2.caffemodel\n"
        "  https://raw.githubusercontent.com/richzhang/colorization/master/colorization/models/colorization_deploy_v2.prototxt\n";
    const string keys =
        "{ h help |                                    | print this help message }"
        "{ proto  | colorization_deploy_v2.prototxt    | model configuration }"
        "{ model  | colorization_release_v2.caffemodel | model weights }"
        "{ image  | space_shuttle.jpg                  | path to image file }"
        "{ opencl |                                    | enable OpenCL }";