//
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// Copyright 2019 Olzhas Zhumabek <anonymous.from.applecity@gmail.com>
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//
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// Use, modification and distribution are subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef BOOST_GIL_IMAGE_PROCESSING_HARRIS_HPP
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#define BOOST_GIL_IMAGE_PROCESSING_HARRIS_HPP
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#include <boost/gil/image_view.hpp>
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#include <boost/gil/typedefs.hpp>
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#include <boost/gil/extension/numeric/kernel.hpp>
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namespace boost { namespace gil {
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/// \defgroup CornerDetectionAlgorithms
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/// \brief Algorithms that are used to find corners in an image
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///
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/// These algorithms are used to find spots from which
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/// sliding the window will produce large intensity change
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/// \brief function to record Harris responses
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/// \ingroup CornerDetectionAlgorithms
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///
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/// This algorithm computes Harris responses
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/// for structure tensor represented by m11, m12_21, m22 views.
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/// Note that m12_21 represents both entries (1, 2) and (2, 1).
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/// Window length represents size of a window which is slided around
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/// to compute sum of corresponding entries. k is a discrimination
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/// constant against edges (usually in range 0.04 to 0.06).
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/// harris_response is an out parameter that will contain the Harris responses.
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template <typename T, typename Allocator>
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void compute_harris_responses(
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boost::gil::gray32f_view_t m11,
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boost::gil::gray32f_view_t m12_21,
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boost::gil::gray32f_view_t m22,
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boost::gil::detail::kernel_2d<T, Allocator> weights,
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float k,
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boost::gil::gray32f_view_t harris_response)
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{
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if (m11.dimensions() != m12_21.dimensions() || m12_21.dimensions() != m22.dimensions()) {
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throw std::invalid_argument("m prefixed arguments must represent"
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" tensor from the same image");
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}
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auto const window_length = weights.size();
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auto const width = m11.width();
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auto const height = m11.height();
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auto const half_length = window_length / 2;
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for (auto y = half_length; y < height - half_length; ++y)
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{
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for (auto x = half_length; x < width - half_length; ++x)
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{
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float ddxx = 0;
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float dxdy = 0;
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float ddyy = 0;
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for (gil::gray32f_view_t::coord_t y_kernel = 0;
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y_kernel < window_length;
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++y_kernel) {
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for (gil::gray32f_view_t::coord_t x_kernel = 0;
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x_kernel < window_length;
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++x_kernel) {
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ddxx += m11(x + x_kernel - half_length, y + y_kernel - half_length)
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.at(std::integral_constant<int, 0>{}) * weights.at(x_kernel, y_kernel);
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dxdy += m12_21(x + x_kernel - half_length, y + y_kernel - half_length)
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.at(std::integral_constant<int, 0>{}) * weights.at(x_kernel, y_kernel);
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ddyy += m22(x + x_kernel - half_length, y + y_kernel - half_length)
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.at(std::integral_constant<int, 0>{}) * weights.at(x_kernel, y_kernel);
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}
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}
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auto det = (ddxx * ddyy) - dxdy * dxdy;
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auto trace = ddxx + ddyy;
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auto harris_value = det - k * trace * trace;
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harris_response(x, y).at(std::integral_constant<int, 0>{}) = harris_value;
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}
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}
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}
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}} //namespace boost::gil
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#endif
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