Boost GIL


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 
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 
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
void scale_lanczos(ImageView input_view, ImageView output_view, std::ptrdiff_t a)
Complete Lanczos algorithmThis algorithm does full pass over resulting image and convolves pixels fro...
Definition: scaling.hpp:95
double lanczos(double x, std::ptrdiff_t a)
Lanczos response at point xLanczos response is defined as: x == 0: 1 -a < x && x < a: 0 otherwise: no...
Definition: numeric.hpp:45