fast erosion with vpp

vpp_erode

template <typename I, typename O>
void erode(const I& img, O& out)
{
  auto win = make_array(vint2{-4, 0}, vint2{-3, 0}, vint2{-2, 0}, vint2{-1, 0},
                        vint2{ 1, 0}, vint2{ 2, 0}, vint2{ 3, 0}, vint2{ 4, 0},
                        vint2{0, -7}, vint2{0, -6}, vint2{0, -5}, vint2{0, -4}, vint2{0, -3}, vint2{0, -2}, vint2{0, -1},
                        vint2{0,  1}, vint2{0,  2}, vint2{0,  3}, vint2{0,  4}, vint2{0,  5}, vint2{0,  6}, vint2{0,  7});
  
  auto nbh = const_box_nbh2d<typename I::value_type, 9, 15>(img);
  pixel_wise(nbh, out) | [win] (const auto& n, auto& o)
  {
    auto r = n(0,0);
    for (int i = 0; i < win.size(); i++)
      r = std::min(n(win[i]), r);
    o = r;
  };
}