/*=========================================================================
 *
 *  Copyright Insight Software Consortium
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/
#ifndef itkRGBToLuminanceImageFilter_h
#define itkRGBToLuminanceImageFilter_h

#include "itkUnaryGeneratorImageFilter.h"

namespace itk
{
/** \class RGBToLuminanceImageFilter
 * \brief Converts an RGB image into a grayscale image.
 *
 * This filters converts an RGB image into a Luminance on by computing
 * pixel-wise a linear combination on the Red, Green and Blue channels. The
 * pixel type of the input image must have a GetLuminance() method. This is the
 * case of the itk::RGBPixel class.
 *
 * \ingroup IntensityImageFilters  MultiThreaded
 * \ingroup ITKImageIntensity
 */
namespace Functor
{
template< typename TInput, typename TOutput >
class RGBToLuminance
{
public:
  using ComponentType = typename TInput::ComponentType;
  using RealType = typename itk::NumericTraits< ComponentType >::RealType;

  RGBToLuminance() = default;
  ~RGBToLuminance() = default;
  bool operator!=(const RGBToLuminance &) const
  {
    return false;
  }

  bool operator==(const RGBToLuminance & other) const
  {
    return !( *this != other );
  }

  inline TOutput operator()(const TInput & A) const
  { return static_cast< TOutput >( A.GetLuminance() ); }
};
}

template< typename TInputImage, typename TOutputImage >
class RGBToLuminanceImageFilter:
  public
  UnaryGeneratorImageFilter< TInputImage, TOutputImage >
{
public:
  ITK_DISALLOW_COPY_AND_ASSIGN(RGBToLuminanceImageFilter);

  /** Standard class type aliases. */
  using Self = RGBToLuminanceImageFilter;
  using Superclass = UnaryGeneratorImageFilter< TInputImage, TOutputImage >;
  using Pointer = SmartPointer< Self >;
  using ConstPointer = SmartPointer< const Self >;
  using FunctorType = Functor::RGBToLuminance< typename TInputImage::PixelType,
                                               typename TOutputImage::PixelType >;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** Runtime information support. */
  itkTypeMacro(RGBToLuminanceImageFilter,
               UnaryGeneratorImageFilter);

#ifdef ITK_USE_CONCEPT_CHECKING
  // Begin concept checking
  itkConceptMacro( InputHasNumericTraitsCheck,
                   ( Concept::HasNumericTraits< typename TInputImage::PixelType::ComponentType > ) );
  // End concept checking
#endif

protected:
  RGBToLuminanceImageFilter()
    {
#if !defined( ITK_WRAPPING_PARSER )
      Superclass::SetFunctor(FunctorType());
#endif
    }
  ~RGBToLuminanceImageFilter() override = default;
};
} // end namespace itk

#endif
