FM / image_processing

/usr/include/boost/gil/image_processing/

/usr/include/boost/gil/image_processing

Name	Size	Mode	Actions
filter.hpp	4243	0644	edit dl rm
harris.hpp	3348	0644	edit dl rm
hessian.hpp	2915	0644	edit dl rm
numeric.hpp	10312	0644	edit dl rm
scaling.hpp	4340	0644	edit dl rm
threshold.hpp	16166	0644	edit dl rm

Edit: /usr/include/boost/gil/image_processing/scaling.hpp (4340B)

//
// Copyright 2019 Olzhas Zhumabek <anonymous.from.applecity@gmail.com>
//
// Use, modification and distribution are subject to the Boost Software License,
// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//
#ifndef BOOST_GIL_IMAGE_PROCESSING_SCALING_HPP
#define BOOST_GIL_IMAGE_PROCESSING_SCALING_HPP

#include <boost/gil/image_view.hpp>
#include <boost/gil/rgb.hpp>
#include <boost/gil/pixel.hpp>
#include <boost/gil/image_processing/numeric.hpp>

namespace boost { namespace gil {

/// \defgroup ScalingAlgorithms
/// \brief Algorthims suitable for rescaling
///
/// These algorithms are used to improve image quality after image resizing is made.
///
/// \defgroup DownScalingAlgorithms
/// \ingroup ScalingAlgorithms
/// \brief Algorthims suitable for downscaling
///
/// These algorithms provide best results when used for downscaling. Using for upscaling will
/// probably provide less than good results.
///
/// \brief a single step of lanczos downscaling
/// \ingroup DownScalingAlgorithms
///
/// Use this algorithm to scale down source image into a smaller image with reasonable quality.
/// Do note that having a look at the output once is a good idea, since it might have ringing
/// artifacts.
template <typename ImageView>
void lanczos_at(
    ImageView input_view,
    ImageView output_view,
    typename ImageView::x_coord_t source_x,
    typename ImageView::y_coord_t source_y,
    typename ImageView::x_coord_t target_x,
    typename ImageView::y_coord_t target_y,
    std::ptrdiff_t a)
{
    using x_coord_t = typename ImageView::x_coord_t;
    using y_coord_t = typename ImageView::y_coord_t;
    using pixel_t = typename std::remove_reference<decltype(std::declval<ImageView>()(0, 0))>::type;

// C++11 doesn't allow auto in lambdas
    using channel_t = typename std::remove_reference
        <
            decltype(std::declval<pixel_t>().at(std::integral_constant<int, 0>{}))
        >::type;

pixel_t result_pixel;
    static_transform(result_pixel, result_pixel, [](channel_t) {
        return static_cast<channel_t>(0);
    });
    auto x_zero = static_cast<x_coord_t>(0);
    auto x_one = static_cast<x_coord_t>(1);
    auto y_zero = static_cast<y_coord_t>(0);
    auto y_one = static_cast<y_coord_t>(1);

for (y_coord_t y_i = (std::max)(source_y - static_cast<y_coord_t>(a) + y_one, y_zero);
         y_i <= (std::min)(source_y + static_cast<y_coord_t>(a), input_view.height() - y_one);
         ++y_i)
    {
        for (x_coord_t x_i = (std::max)(source_x - static_cast<x_coord_t>(a) + x_one, x_zero);
             x_i <= (std::min)(source_x + static_cast<x_coord_t>(a), input_view.width() - x_one);
             ++x_i)
        {
            double lanczos_response = lanczos(source_x - x_i, a) * lanczos(source_y - y_i, a);
            auto op = [lanczos_response](channel_t prev, channel_t next)
            {
                return static_cast<channel_t>(prev + next * lanczos_response);
            };
            static_transform(result_pixel, input_view(source_x, source_y), result_pixel, op);
        }
    }

output_view(target_x, target_y) = result_pixel;
}

/// \brief Complete Lanczos algorithm
/// \ingroup DownScalingAlgorithms
///
/// This algorithm does full pass over resulting image and convolves pixels from
/// original image. Do note that it might be a good idea to have a look at test
/// output as there might be ringing artifacts.
/// Based on wikipedia article:
/// https://en.wikipedia.org/wiki/Lanczos_resampling
/// with standardinzed cardinal sin (sinc)
template <typename ImageView>
void scale_lanczos(ImageView input_view, ImageView output_view, std::ptrdiff_t a)
{
    double scale_x = (static_cast<double>(output_view.width()))
                     / static_cast<double>(input_view.width());
    double scale_y = (static_cast<double>(output_view.height()))
                     / static_cast<double>(input_view.height());

using x_coord_t = typename ImageView::x_coord_t;
    using y_coord_t = typename ImageView::y_coord_t;
    for (y_coord_t y = 0; y < output_view.height(); ++y)
    {
        for (x_coord_t x = 0; x < output_view.width(); ++x)
        {
            lanczos_at(input_view, output_view, x / scale_x, y / scale_y, x, y, a);
        }
    }
}

}} // namespace boost::gil

#endif

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