rgb_to_hsi.hh

// Copyright (C) 2008, 2009 EPITA Research and Development Laboratory (LRDE)
//
// This file is part of Olena.
//
// Olena is free software: you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free
// Software Foundation, version 2 of the License.
//
// Olena is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Olena.  If not, see <http://www.gnu.org/licenses/>.
//
// As a special exception, you may use this file as part of a free
// software project without restriction.  Specifically, if other files
// instantiate templates or use macros or inline functions from this
// file, or you compile this file and link it with other files to produce
// an executable, this file does not by itself cause the resulting
// executable to be covered by the GNU General Public License.  This
// exception does not however invalidate any other reasons why the
// executable file might be covered by the GNU General Public License.

#ifndef MLN_FUN_V2V_RGB_TO_HSI_HH
# define MLN_FUN_V2V_RGB_TO_HSI_HH

#include <cmath>

#include <mln/value/rgb8.hh>
#include <mln/math/round.hh>

#include <mln/value/hsi.hh>


namespace mln
{


  namespace fun
  {

    namespace v2v
    {

      template <typename T_hsi>
      struct f_rgb_to_hsi_ : public Function_v2v< f_rgb_to_hsi_<T_hsi> >
      {
        typedef T_hsi result;

        template <typename T_rgb>
        T_hsi operator()(const T_rgb& rgb) const;

      };

      typedef f_rgb_to_hsi_<value::hsi_f> f_rgb_to_hsi_f_t;

      extern f_rgb_to_hsi_f_t f_rgb_to_hsi_f;


# ifndef MLN_INCLUDE_ONLY

      f_rgb_to_hsi_f_t f_rgb_to_hsi_f;


      template <typename T_hsi>
      template <typename T_rgb>
      inline
      T_hsi
      f_rgb_to_hsi_<T_hsi>::operator()(const T_rgb& rgb) const
      {
        // Locals.
        static const double sqrt3_3 = std::sqrt(3) / 3;
        static const double inv_sqrt6 = 1 / std::sqrt(6);
        static const double inv_sqrt2 = 1 / std::sqrt(2);

        T_hsi hsi;

        double alpha = inv_sqrt2 * rgb.green() - inv_sqrt2 * rgb.blue();
        double beta =
          2 * inv_sqrt6 * rgb.red() -
          inv_sqrt6 * rgb.green() -
          inv_sqrt6 * rgb.blue();


        hsi.hue() = atan2(beta, alpha) / 3.1415 * 180.0;
        if (hsi.hue() < 0)
          hsi.hue() = hsi.hue() + 360.0;
        mln_invariant(hsi.hue() >= 0);
        hsi.sat() = std::sqrt(alpha * alpha + beta * beta);
        hsi.inty() =
          sqrt3_3 * rgb.red() +
          sqrt3_3 * rgb.green() +
          sqrt3_3 * rgb.blue();

        return hsi;
      }


# endif // !MLN_INCLUDE_ONLY

    } // end of namespace fun::v2v

  } // end of namespace fun

} // end of namespace mln

#endif // ! MLN_FUN_V2V_RGB_TO_HSI_HH