    // Copyright (C) 2010  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_IMAGE_PYRaMID_ABSTRACT_H__
    #ifdef DLIB_IMAGE_PYRaMID_ABSTRACT_H__

    #include "../pixel.h"
    #include "../array2d.h"
    #include "../geometry.h"

    namespace dlib
    {

        template <
            unsigned int N
            >
        class pyramid_down : noncopyable
        {
            /*!
                REQUIREMENTS ON N
                    N > 0

                WHAT THIS OBJECT REPRESENTS
                    This is a simple functor to help create image pyramids.  In particular, it
                    downsamples images at a ratio of N to N-1.

                    Note that setting N to 1 means that this object functions like
                    pyramid_disable (defined at the bottom of this file).

                    WARNING, when mapping rectangles from one layer of a pyramid
                    to another you might end up with rectangles which extend slightly
                    outside your images.  This is because points on the border of an
                    image at a higher pyramid layer might correspond to points outside
                    images at lower layers.  So just keep this in mind.  Note also
                    that it's easy to deal with.  Just say something like this:
                        rect = rect.intersect(get_rect(my_image)); // keep rect inside my_image
            !*/
        public:

            template <
                typename in_image_type,
                typename out_image_type
                >
            void operator() (
                const in_image_type& original,
                out_image_type& down
            ) const;
            /*!
                requires
                    - is_same_object(original, down) == false
                    - in_image_type == is an implementation of array2d/array2d_kernel_abstract.h
                    - out_image_type == is an implementation of array2d/array2d_kernel_abstract.h
                    - pixel_traits<typename in_image_type::type>::has_alpha == false
                    - pixel_traits<typename out_image_type::type>::has_alpha == false
                ensures
                    - #down will contain an image that is roughly (N-1)/N times the size of the
                      original image.
                    - If both input and output images contain RGB pixels then the downsampled image will
                      be in color.  Otherwise, the downsampling will be performed in a grayscale mode.
                    - The location of a point P in original image will show up at point point_down(P)
                      in the #down image.
                    - Note that some points on the border of the original image might correspond to
                      points outside the #down image.
            !*/

        // -------------------------------

            template <typename T>
            vector<double,2> point_down (
                const vector<T,2>& p
            ) const;
            /*!
                ensures
                    - interprets p as a point in a parent image and returns the
                      point in a downsampled image which corresponds to p.
                    - This function is the inverse of point_up().  I.e. for a point P:
                      point_down(point_up(P)) == P
            !*/

            template <typename T>
            vector<double,2> point_up (
                const vector<T,2>& p
            ) const;
            /*!
                ensures
                    - interprets p as a point in a downsampled image and returns the
                      point in a parent image which corresponds to p.
                    - This function is the inverse of point_down().  I.e. for a point P:
                      point_up(point_down(P)) == P
            !*/

            rectangle rect_down (
                const rectangle& rect
            ) const;
            /*!
                ensures
                    - returns rectangle(point_down(rect.tl_corner()), point_down(rect.br_corner()));
                      (i.e. maps rect into a downsampled)
            !*/

            rectangle rect_up (
                const rectangle& rect
            ) const;
            /*!
                ensures
                    - returns rectangle(point_up(rect.tl_corner()), point_up(rect.br_corner()));
                      (i.e. maps rect into a parent image)
            !*/

        // -------------------------------

            template <typename T>
            vector<double,2> point_down (
                const vector<T,2>& p,
                unsigned int levels
            ) const;
            /*!
                ensures
                    - applies point_down() to p levels times and returns the result.
                      (i.e. point_down(p,2) == point_down(point_down(p)),
                            point_down(p,1) == point_down(p),
                            point_down(p,0) == p,  etc. )
            !*/

            template <typename T>
            vector<double,2> point_up (
                const vector<T,2>& p,
                unsigned int levels
            ) const;
            /*!
                ensures
                    - applies point_up() to p levels times and returns the result.
                      (i.e. point_up(p,2) == point_up(point_up(p)),
                            point_up(p,1) == point_up(p),
                            point_up(p,0) == p,  etc. )
            !*/

            rectangle rect_down (
                const rectangle& rect,
                unsigned int levels
            ) const;
            /*!
                ensures
                    - returns rectangle(point_down(rect.tl_corner(),levels), point_down(rect.br_corner(),levels));
                      (i.e. Basically applies rect_down() to rect levels times and returns the result.)
            !*/

            rectangle rect_up (
                const rectangle& rect,
                unsigned int levels
            ) const;
            /*!
                ensures
                    - returns rectangle(point_up(rect.tl_corner(),levels), point_up(rect.br_corner(),levels));
                      (i.e. Basically applies rect_up() to rect levels times and returns the result.)
            !*/

        };

    // ----------------------------------------------------------------------------------------

        class pyramid_disable : noncopyable
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This is a function object with an interface identical to pyramid_down (defined
                    at the top of this file) except that it downsamples images at a ratio of infinity
                    to 1.  That means it always outputs images of size 0 regardless of the size
                    of the inputs.

                    This is useful because it can be supplied to routines which take a pyramid_down
                    function object and it will essentially disable pyramid processing.  This way,
                    a pyramid oriented function can be turned into a regular routine which processes
                    just the original undownsampled image.
            !*/
        };

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_IMAGE_PYRaMID_ABSTRACT_H__