extern int flow_enable, flow_window, flow_levels, flow_iter, flow_view_vector, flow_view_uv;
void flow_default(void);
-void save_flow(const char *filename);
-int load_flow(const char *filename);
void *create_flow_maps(const double *img_prev_buffer, const double *img_next_buffer, const double *img_buffer, int width, int height, int win_size, int steps, double *flow_map_x_prev, double *flow_map_y_prev, double *flow_map_x_next, double *flow_map_y_next, void *_image_preview);