double image_sum(const SDoublePlane& input) {
double *start = input.data_ptr();
double *end = start + input.rows()*input.cols();
return std::accumulate(start, end, 0);
}
double image_max(const SDoublePlane& input) {
double *start = input.data_ptr();
double *end = start + input.rows()*input.cols();
double *pos = std::max_element(start, end);
return (pos == end)? -1.0: *pos;
}