81 lines
3.2 KiB
C++
81 lines
3.2 KiB
C++
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//
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// Copyright 2019 Olzhas Zhumabek <anonymous.from.applecity@gmail.com>
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// Copyright 2021 Scramjet911 <36035352+Scramjet911@users.noreply.github.com>
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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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#ifndef BOOST_GIL_IMAGE_PROCESSING_HESSIAN_HPP
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#define BOOST_GIL_IMAGE_PROCESSING_HESSIAN_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/image_processing/kernel.hpp>
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#include <stdexcept>
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namespace boost { namespace gil {
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/// \brief Computes Hessian response
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///
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/// Computes Hessian response based on computed entries of Hessian matrix, e.g. second order
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/// derivates in x and y, and derivatives in both x, y.
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/// d stands for derivative, and x or y stand for derivative direction. For example,
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/// ddxx means taking two derivatives (gradients) in horizontal direction.
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/// Weights change perception of surroinding pixels.
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/// Additional filtering is strongly advised.
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template <typename GradientView, typename T, typename Allocator, typename OutputView>
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inline void compute_hessian_responses(
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GradientView ddxx,
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GradientView dxdy,
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GradientView ddyy,
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const detail::kernel_2d<T, Allocator>& weights,
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OutputView dst)
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{
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if (ddxx.dimensions() != ddyy.dimensions()
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|| ddyy.dimensions() != dxdy.dimensions()
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|| dxdy.dimensions() != dst.dimensions()
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|| weights.center_x() != weights.center_y())
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{
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throw std::invalid_argument("dimensions of views are not the same"
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" or weights don't have equal width and height"
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" or weights' dimensions are not odd");
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}
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// Use pixel type of output, as values will be written to output
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using pixel_t = typename std::remove_reference<decltype(std::declval<OutputView>()(0, 0))>::type;
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using channel_t = typename std::remove_reference
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<
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decltype(std::declval<pixel_t>().at(std::integral_constant<int, 0>{}))
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>::type;
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auto center = weights.center_y();
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for (auto y = center; y < dst.height() - center; ++y)
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{
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for (auto x = center; x < dst.width() - center; ++x)
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{
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auto ddxx_i = channel_t();
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auto ddyy_i = channel_t();
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auto dxdy_i = channel_t();
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for (typename OutputView::coord_t w_y = 0; w_y < static_cast<std::ptrdiff_t>(weights.size()); ++w_y)
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{
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for (typename OutputView::coord_t w_x = 0; w_x < static_cast<std::ptrdiff_t>(weights.size()); ++w_x)
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{
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ddxx_i += ddxx(x + w_x - center, y + w_y - center)
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.at(std::integral_constant<int, 0>{}) * weights.at(w_x, w_y);
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ddyy_i += ddyy(x + w_x - center, y + w_y - center)
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.at(std::integral_constant<int, 0>{}) * weights.at(w_x, w_y);
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dxdy_i += dxdy(x + w_x - center, y + w_y - center)
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.at(std::integral_constant<int, 0>{}) * weights.at(w_x, w_y);
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}
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}
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auto determinant = ddxx_i * ddyy_i - dxdy_i * dxdy_i;
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dst(x, y).at(std::integral_constant<int, 0>{}) = determinant;
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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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