Harris response computation

example/Jamfile

@@ -22,6 +22,7 @@ local sources =
     affine.cpp
     dynamic_image.cpp
     histogram.cpp
+    harris.cpp
     ;
 
 local targets ;

example/harris.cpp

@@ -0,0 +1,262 @@
+//
+// 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)
+//
+#include <boost/gil/image.hpp>
+#include <boost/gil/image_view.hpp>
+#include <boost/gil/extension/io/png.hpp>
+#include <boost/gil/image_processing/numeric.hpp>
+#include <boost/gil/image_processing/harris.hpp>
+#include <vector>
+#include <functional>
+#include <set>
+#include <iostream>
+#include <fstream>
+
+namespace gil = boost::gil;
+
+// some images might produce artifacts
+// when converted to grayscale,
+// which was previously observed on
+// canny edge detector for test input
+// used for this example
+gil::gray8_image_t to_grayscale(gil::rgb8_view_t original)
+{
+    gil::gray8_image_t output_image(original.dimensions());
+    auto output = gil::view(output_image);
+    constexpr double max_channel_intensity = (std::numeric_limits<std::uint8_t>::max)();
+    for (long int y = 0; y < original.height(); ++y) {
+        for (long int x = 0; x < original.width(); ++x) {
+            // scale the values into range [0, 1] and calculate linear intensity
+            double red_intensity = original(x, y).at(std::integral_constant<int, 0>{})
+                / max_channel_intensity;
+            double green_intensity = original(x, y).at(std::integral_constant<int, 1>{})
+                / max_channel_intensity;
+            double blue_intensity = original(x, y).at(std::integral_constant<int, 2>{})
+                / max_channel_intensity;
+            auto linear_luminosity = 0.2126 * red_intensity
+                                    + 0.7152 * green_intensity
+                                    + 0.0722 * blue_intensity;
+
+            // perform gamma adjustment
+            double gamma_compressed_luminosity = 0;
+            if (linear_luminosity < 0.0031308) {
+                gamma_compressed_luminosity = linear_luminosity * 12.92;
+            } else {
+                gamma_compressed_luminosity = 1.055 * std::pow(linear_luminosity, 1 / 2.4) - 0.055;
+            }
+
+            // since now it is scaled, descale it back
+            output(x, y) = gamma_compressed_luminosity * max_channel_intensity;
+        }
+    }
+
+    return output_image;
+}
+
+void apply_gaussian_blur(gil::gray8_view_t input_view, gil::gray8_view_t output_view)
+{
+    constexpr static auto filterHeight = 5ull;
+    constexpr static auto filterWidth = 5ull;
+    constexpr static double filter[filterHeight][filterWidth] =
+    {
+        2,  4,  6,  4,  2,
+        4, 9, 12, 9,  4,
+        5, 12, 15, 12,  5,
+        4, 9, 12, 9,  4,
+        2,  4,  5,  4,  2,
+    };
+    constexpr double factor = 1.0 / 159;
+    constexpr double bias = 0.0;
+
+    const auto height = input_view.height();
+    const auto width = input_view.width();
+    for (long x = 0; x < width; ++x) {
+        for (long y = 0; y < height; ++y) {
+            double intensity = 0.0;
+            for (size_t filter_y = 0; filter_y < filterHeight; ++filter_y) {
+                for (size_t filter_x = 0; filter_x < filterWidth; ++filter_x) {
+                    int image_x = x - filterWidth / 2 + filter_x;
+                    int image_y = y - filterHeight / 2 + filter_y;
+                    if (image_x >= input_view.width() || image_x < 0
+                        || image_y >= input_view.height() || image_y < 0) {
+                        continue;
+                    }
+                    auto& pixel = input_view(image_x, image_y);
+                    intensity += pixel.at(std::integral_constant<int, 0>{})
+                        * filter[filter_y][filter_x];
+                }
+            }
+            auto& pixel = output_view(gil::point_t(x, y));
+            pixel = (std::min)((std::max)(int(factor * intensity + bias), 0), 255);
+        }
+
+    }
+}
+
+void calculate_gradients(gil::gray8_view_t input,
+    gil::gray16_view_t x_gradient,
+    gil::gray16_view_t y_gradient)
+{
+    using x_coord_t = gil::gray16_view_t::x_coord_t;
+    using y_coord_t = gil::gray16_view_t::y_coord_t;
+    using pixel_t = std::remove_reference<decltype(x_gradient(0, 0))>::type;
+    using channel_t = typename std::remove_reference<
+                        decltype(
+                            std::declval<gil::gray16_pixel_t>().at(
+                                std::integral_constant<int, 0>{}
+                            )
+                        )
+                       >::type;
+
+    constexpr double x_kernel[3][3] =
+    {
+        {1, 0, -1},
+        {2, 0, -2},
+        {1, 0, -1}
+    };
+    constexpr double y_kernel[3][3] =
+    {
+        {1, 2, 1},
+        {0, 0, 0},
+        {-1, -2, -1}
+    };
+    constexpr auto chosen_channel = std::integral_constant<int, 0>{};
+    for (y_coord_t y = 1; y < input.height() - 1; ++y)
+    {
+        for (x_coord_t x = 1; x < input.width() - 1; ++x)
+        {
+            gil::gray16_pixel_t x_result;
+            boost::gil::static_transform(x_result, x_result,
+                [](channel_t) { return static_cast<channel_t>(0); });
+            gil::gray16_pixel_t y_result;
+            boost::gil::static_transform(y_result, y_result,
+                [](channel_t) { return static_cast<channel_t>(0); });
+            for (y_coord_t y_filter = 0; y_filter < 2; ++y_filter)
+            {
+                for (x_coord_t x_filter = 0; x_filter < 2; ++x_filter)
+                {
+                    auto adjusted_y = y + y_filter - 1;
+                    auto adjusted_x = x + x_filter - 1;
+                    x_result.at(std::integral_constant<int, 0>{}) +=
+                        input(adjusted_x, adjusted_y).at(chosen_channel)
+                        * x_kernel[y_filter][x_filter];
+                    y_result.at(std::integral_constant<int, 0>{}) +=
+                        input(adjusted_x, adjusted_y).at(chosen_channel)
+                        * y_kernel[y_filter][x_filter];
+                }
+            }
+            x_gradient(x, y) = static_cast<std::uint8_t>(x_result.at(chosen_channel));
+            y_gradient(x, y) = static_cast<std::uint8_t>(y_result.at(chosen_channel));
+        }
+    }
+}
+
+std::vector<gil::point_t> suppress(
+    gil::gray32f_view_t harris_response,
+    double harris_response_threshold)
+{
+    std::vector<gil::point_t> corner_points;
+    for (gil::gray32f_view_t::coord_t y = 1; y < harris_response.height() - 1; ++y)
+    {
+        for (gil::gray32f_view_t::coord_t x = 1; x < harris_response.width() - 1; ++x)
+        {
+            auto value = [](gil::gray32f_pixel_t pixel) {
+                return pixel.at(std::integral_constant<int, 0>{});
+            };
+            double values[9] = {
+                value(harris_response(x - 1, y - 1)),
+                value(harris_response(x, y - 1)),
+                value(harris_response(x + 1, y - 1)),
+                value(harris_response(x - 1, y)),
+                value(harris_response(x, y)),
+                value(harris_response(x + 1, y)),
+                value(harris_response(x - 1, y + 1)),
+                value(harris_response(x, y + 1)),
+                value(harris_response(x + 1, y + 1))
+            };
+
+            auto maxima = *std::max_element(
+                values,
+                values + 9,
+                [](double lhs, double rhs)
+                {
+                    return lhs < rhs;
+                }
+            );
+
+            if (maxima == value(harris_response(x, y))
+                && std::count(values, values + 9, maxima) == 1
+                && maxima >= harris_response_threshold)
+            {
+                corner_points.emplace_back(x, y);
+            }
+        }
+    }
+
+    return corner_points;
+}
+
+int main(int argc, char* argv[])
+{
+    if (argc != 6)
+    {
+        std::cout << "usage: " << argv[0] << " <input.png> <odd-window-size>"
+            " <discrimination-constant> <harris-response-threshold> <output.png>\n";
+        return -1;
+    }
+
+    long int window_size = std::stoi(argv[2]);
+    double discrimnation_constant = std::stod(argv[3]);
+    long harris_response_threshold = std::stol(argv[4]);
+
+    gil::rgb8_image_t input_image;
+
+    gil::read_image(argv[1], input_image, gil::png_tag{});
+
+    auto input_view = gil::view(input_image);
+    auto grayscaled = to_grayscale(input_view);
+    gil::gray8_image_t smoothed_image(grayscaled.dimensions());
+    auto smoothed = gil::view(smoothed_image);
+    apply_gaussian_blur(gil::view(grayscaled), smoothed);
+    gil::gray16_image_t x_gradient_image(grayscaled.dimensions());
+    gil::gray16_image_t y_gradient_image(grayscaled.dimensions());
+
+    auto x_gradient = gil::view(x_gradient_image);
+    auto y_gradient = gil::view(y_gradient_image);
+    calculate_gradients(smoothed, x_gradient, y_gradient);
+
+    gil::gray32f_image_t m11(x_gradient.dimensions());
+    gil::gray32f_image_t m12_21(x_gradient.dimensions());
+    gil::gray32f_image_t m22(x_gradient.dimensions());
+    gil::compute_tensor_entries(
+        x_gradient,
+        y_gradient,
+        gil::view(m11),
+        gil::view(m12_21),
+        gil::view(m22)
+    );
+
+    gil::gray32f_image_t harris_response(x_gradient.dimensions());
+    gil::gray32f_image_t gaussian_kernel(gil::point_t(5, 5));
+    gil::generate_gaussian_kernel(gil::view(gaussian_kernel), 0.84089642);
+    gil::compute_harris_responses(
+        gil::view(m11),
+        gil::view(m12_21),
+        gil::view(m22),
+        gil::view(gaussian_kernel),
+        discrimnation_constant,
+        gil::view(harris_response)
+    );
+
+    auto corner_points = suppress(gil::view(harris_response), harris_response_threshold);
+    for (auto point: corner_points)
+    {
+        input_view(point) = gil::rgb8_pixel_t(0, 0, 0);
+        input_view(point).at(std::integral_constant<int, 1>{}) = 255;
+    }
+    gil::write_view(argv[5], input_view, gil::png_tag{});
+}

include/boost/gil/image_processing/harris.hpp

@@ -0,0 +1,83 @@
+//
+// 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_HARRIS_HPP
+#define BOOST_GIL_IMAGE_PROCESSING_HARRIS_HPP
+
+#include <boost/gil/image_view.hpp>
+#include <boost/gil/typedefs.hpp>
+
+namespace boost { namespace gil {
+/// \defgroup CornerDetectionAlgorithms
+/// \brief Algorithms that are used to find corners in an image
+///
+/// These algorithms are used to find spots from which
+/// sliding the window will produce large intensity change
+
+
+/// \brief function to record Harris responses
+/// \ingroup CornerDetectionAlgorithms
+///
+/// This algorithm computes Harris responses
+/// for structure tensor represented by m11, m12_21, m22 views.
+/// Note that m12_21 represents both entries (1, 2) and (2, 1).
+/// Window length represents size of a window which is slided around
+/// to compute sum of corresponding entries. k is a discrimination
+/// constant against edges (usually in range 0.04 to 0.06).
+/// harris_response is an out parameter that will contain the Harris responses.
+void compute_harris_responses(
+    boost::gil::gray32f_view_t m11,
+    boost::gil::gray32f_view_t m12_21,
+    boost::gil::gray32f_view_t m22,
+    boost::gil::gray32f_view_t weights,
+    float k,
+    boost::gil::gray32f_view_t harris_response)
+{
+    if (m11.dimensions() != m12_21.dimensions() || m12_21.dimensions() != m22.dimensions()) {
+        throw std::invalid_argument("m prefixed arguments must represent"
+            " tensor from the same image");
+    }
+
+    auto const window_length = weights.dimensions().x;
+    auto const width = m11.width();
+    auto const height = m11.height();
+    auto const half_length = window_length / 2;
+
+    for (auto y = half_length; y < height - half_length; ++y)
+    {
+        for (auto x = half_length; x < width - half_length; ++x)
+        {
+            float ddxx = 0;
+            float dxdy = 0;
+            float ddyy = 0;
+            for (gil::gray32f_view_t::coord_t y_kernel = 0;
+                y_kernel < window_length;
+                ++y_kernel) {
+                for (gil::gray32f_view_t::coord_t x_kernel = 0;
+                    x_kernel < window_length;
+                    ++x_kernel) {
+                    ddxx += m11(x + x_kernel - half_length, y + y_kernel - half_length)
+                        .at(std::integral_constant<int, 0>{})
+                        * weights(x_kernel, y_kernel).at(std::integral_constant<int, 0>{});
+                    dxdy += m12_21(x + x_kernel - half_length, y + y_kernel - half_length)
+                        .at(std::integral_constant<int, 0>{})
+                        * weights(x_kernel, y_kernel).at(std::integral_constant<int, 0>{});
+                    ddyy += m22(x + x_kernel - half_length, y + y_kernel - half_length)
+                        .at(std::integral_constant<int, 0>{})
+                        * weights(x_kernel, y_kernel).at(std::integral_constant<int, 0>{});
+                }
+            }
+            auto det = (ddxx * ddyy) - dxdy * dxdy;
+            auto trace = ddxx + ddyy;
+            auto harris_value = det - k * trace * trace;
+            harris_response(x, y).at(std::integral_constant<int, 0>{}) = harris_value;
+        }
+    }
+}
+
+}} //namespace boost::gil
+#endif

include/boost/gil/image_processing/numeric.hpp

@@ -50,6 +50,24 @@ inline double lanczos(double x, std::ptrdiff_t a)
     return 0;
 }
 
+inline void compute_tensor_entries(
+    boost::gil::gray16_view_t dx,
+    boost::gil::gray16_view_t dy,
+    boost::gil::gray32f_view_t m11,
+    boost::gil::gray32f_view_t m12_21,
+    boost::gil::gray32f_view_t m22)
+{
+    for (std::ptrdiff_t y = 0; y < dx.height(); ++y) {
+        for (std::ptrdiff_t x = 0; x < dx.width(); ++x) {
+            auto dx_value = dx(x, y);
+            auto dy_value = dy(x, y);
+            m11(x, y) = dx_value * dx_value;
+            m12_21(x, y) = dx_value * dy_value;
+            m22(x, y) = dy_value * dy_value;
+        }
+    }
+}
+
 /// \brief Generate mean kernel
 /// \ingroup ImageProcessingMath
 ///

test/core/image_processing/CMakeLists.txt

@@ -29,7 +29,8 @@ endforeach()
 
 foreach(_name
   lanczos_scaling
-  simple_kernels)
+  simple_kernels
+  harris)
   set(_test t_core_image_processing_${_name})
   set(_target test_core_image_processing_${_name})
 

test/core/image_processing/Jamfile

@@ -19,3 +19,4 @@ run threshold_truncate.cpp ;
 run threshold_otsu.cpp ;
 run lanczos_scaling.cpp ;
 run simple_kernels.cpp ;
+run harris.cpp ;