// -------------------------------------------------------------------------
// @author Leonardo Florez-Valencia (florez-l@javeriana.edu.co)
// -------------------------------------------------------------------------

#ifndef __CPEXTENSIONS__ALGORITHMS__RGBTOHSVFUNCTION__H__
#define __CPEXTENSIONS__ALGORITHMS__RGBTOHSVFUNCTION__H__

#include <cmath>
#include <limits>
#include <vnl/vnl_math.h>

#include <itkRGBPixel.h>

namespace cpExtensions
{
  namespace Algorithms
  {
    /**
     */
    template< class P >
    struct RGBToHSVFunction
    {
      typedef RGBToHSVFunction      Self;
      typedef P                     TOutPixel;
      typedef typename P::ValueType TValue;

      template< class Tr, class Tg, class Tb >
      P operator()( const Tr& r, const Tg& g, const Tb& b ) const
        {
          static const double mVal =
            double( std::numeric_limits< TValue >::max( ) );
          static const double _0 = double( 0 );
          static const double _1 = double( 1 );
          static const double _2 = double( 2 );
          static const double _3 = double( 3 );
          static const double _2pi = _2 * double( vnl_math::pi );

          P hsv;

          double R = double( r );
          double G = double( g );
          double B = double( b );
          double sRGB = R + G + B;
          double RG = R - G;
          double RB = R - B;
          double GB = G - B;

          // Hue
          double A = std::sqrt( ( RG * RG ) + ( RB * GB ) );
          if( A != _0 )
            A = std::acos( ( RG + RB ) / ( _2 * A ) );
          A /= _2pi;
          hsv[ 0 ] = TValue( mVal * ( ( G >= B )? A: _1 - A ) );

          // Saturation
          if( sRGB != _0 )
          {
            double C = ( G < R )? G: R;
            C        = ( B < C )? B: C;
            hsv[ 1 ] = TValue( mVal * ( _1 - ( ( _3 * C ) / sRGB ) ) );
          }
          else
            hsv[ 1 ] = TValue( 0 );

          // Value
          hsv[ 2 ] = TValue( sRGB / _3 );
          return( hsv );
        }

      template< class C >
      TOutPixel operator()( const itk::RGBPixel< C >& rgb ) const
        {
          return(
            this->operator()(
              rgb.GetRed( ), rgb.GetGreen( ), rgb.GetBlue( )
              )
            );
        }
    };

  } // ecapseman

} // ecapseman

#endif // __CPEXTENSIONS__ALGORITHMS__RGBTOHSVFUNCTION__H__

// eof - $RCSfile$