ceph/src/boost/boost/gil/image_processing/scaling.hpp

   1 //
   2 // Copyright 2019 Olzhas Zhumabek <anonymous.from.applecity@gmail.com>
   3 //
   4 // Use, modification and distribution are subject to the Boost Software License,
   5 // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt)
   7 //
   8 #ifndef BOOST_GIL_IMAGE_PROCESSING_SCALING_HPP
   9 #define BOOST_GIL_IMAGE_PROCESSING_SCALING_HPP
  10
  11 #include <boost/gil/image_view.hpp>
  12 #include <boost/gil/rgb.hpp>
  13 #include <boost/gil/pixel.hpp>
  14 #include <boost/gil/image_processing/numeric.hpp>
  15
  16 namespace boost { namespace gil {
  17
  18 /// \defgroup ScalingAlgorithms
  19 /// \brief Algorthims suitable for rescaling
  20 ///
  21 /// These algorithms are used to improve image quality after image resizing is made.
  22 ///
  23 /// \defgroup DownScalingAlgorithms
  24 /// \ingroup ScalingAlgorithms
  25 /// \brief Algorthims suitable for downscaling
  26 ///
  27 /// These algorithms provide best results when used for downscaling. Using for upscaling will
  28 /// probably provide less than good results.
  29 ///
  30 /// \brief a single step of lanczos downscaling
  31 /// \ingroup DownScalingAlgorithms
  32 ///
  33 /// Use this algorithm to scale down source image into a smaller image with reasonable quality.
  34 /// Do note that having a look at the output once is a good idea, since it might have ringing
  35 /// artifacts.
  36 template <typename ImageView>
  37 void lanczos_at(
  38     ImageView input_view,
  39     ImageView output_view,
  40     typename ImageView::x_coord_t source_x,
  41     typename ImageView::y_coord_t source_y,
  42     typename ImageView::x_coord_t target_x,
  43     typename ImageView::y_coord_t target_y,
  44     std::ptrdiff_t a)
  45 {
  46     using x_coord_t = typename ImageView::x_coord_t;
  47     using y_coord_t = typename ImageView::y_coord_t;
  48     using pixel_t = typename std::remove_reference<decltype(std::declval<ImageView>()(0, 0))>::type;
  49
  50     // C++11 doesn't allow auto in lambdas
  51     using channel_t = typename std::remove_reference
  52         <
  53             decltype(std::declval<pixel_t>().at(std::integral_constant<int, 0>{}))
  54         >::type;
  55
  56     pixel_t result_pixel;
  57     static_transform(result_pixel, result_pixel, [](channel_t) {
  58         return static_cast<channel_t>(0);
  59     });
  60     auto x_zero = static_cast<x_coord_t>(0);
  61     auto x_one = static_cast<x_coord_t>(1);
  62     auto y_zero = static_cast<y_coord_t>(0);
  63     auto y_one = static_cast<y_coord_t>(1);
  64
  65     for (y_coord_t y_i = (std::max)(source_y - static_cast<y_coord_t>(a) + y_one, y_zero);
  66          y_i <= (std::min)(source_y + static_cast<y_coord_t>(a), input_view.height() - y_one);
  67          ++y_i)
  68     {
  69         for (x_coord_t x_i = (std::max)(source_x - static_cast<x_coord_t>(a) + x_one, x_zero);
  70              x_i <= (std::min)(source_x + static_cast<x_coord_t>(a), input_view.width() - x_one);
  71              ++x_i)
  72         {
  73             double lanczos_response = lanczos(source_x - x_i, a) * lanczos(source_y - y_i, a);
  74             auto op = [lanczos_response](channel_t prev, channel_t next)
  75             {
  76                 return static_cast<channel_t>(prev + next * lanczos_response);
  77             };
  78             static_transform(result_pixel, input_view(source_x, source_y), result_pixel, op);
  79         }
  80     }
  81
  82     output_view(target_x, target_y) = result_pixel;
  83 }
  84
  85 /// \brief Complete Lanczos algorithm
  86 /// \ingroup DownScalingAlgorithms
  87 ///
  88 /// This algorithm does full pass over resulting image and convolves pixels from
  89 /// original image. Do note that it might be a good idea to have a look at test
  90 /// output as there might be ringing artifacts.
  91 /// Based on wikipedia article:
  92 /// https://en.wikipedia.org/wiki/Lanczos_resampling
  93 /// with standardinzed cardinal sin (sinc)
  94 template <typename ImageView>
  95 void scale_lanczos(ImageView input_view, ImageView output_view, std::ptrdiff_t a)
  96 {
  97     double scale_x = (static_cast<double>(output_view.width()))
  98                      / static_cast<double>(input_view.width());
  99     double scale_y = (static_cast<double>(output_view.height()))
 100                      / static_cast<double>(input_view.height());
 101
 102     using x_coord_t = typename ImageView::x_coord_t;
 103     using y_coord_t = typename ImageView::y_coord_t;
 104     for (y_coord_t y = 0; y < output_view.height(); ++y)
 105     {
 106         for (x_coord_t x = 0; x < output_view.width(); ++x)
 107         {
 108             lanczos_at(input_view, output_view, x / scale_x, y / scale_y, x, y, a);
 109         }
 110     }
 111 }
 112
 113 }} // namespace boost::gil
 114
 115 #endif