diff --git a/.clang-tidy b/.clang-tidy
new file mode 100644
index 0000000..b0c1f1e
--- /dev/null
+++ b/.clang-tidy
@@ -0,0 +1 @@
+Checks: 'performance-*,portability-*,readability-*,clang-analyzer-*,bugprone-*,modernize-*'
\ No newline at end of file
diff --git a/HDRI/debevec_weight.hpp b/HDRI/debevec_weight.hpp
index 29112ca..6543781 100644
--- a/HDRI/debevec_weight.hpp
+++ b/HDRI/debevec_weight.hpp
@@ -7,7 +7,7 @@ namespace HDRI {
 class debevec_weight final {
  public:
   debevec_weight() = delete;
-  [[nodiscard]] static double get_weight(const int index) noexcept;
+  [[nodiscard]] static double get_weight(const int z_value) noexcept;
   [[nodiscard]] static std::size_t get_size() noexcept;
 };
 
diff --git a/HDRI/hdr_image.cpp b/HDRI/hdr_image.cpp
index f22bffe..d226c97 100644
--- a/HDRI/hdr_image.cpp
+++ b/HDRI/hdr_image.cpp
@@ -12,8 +12,8 @@
 namespace {
 
 template <typename weight_function>
-cv::Mat construct_radiance(const std::vector<HDRI::raw_image> &image_files, const std::array<cv::Mat, 3UL> &curves,
-                           weight_function &&weighting, const std::vector<double> &expo) noexcept {
+auto construct_radiance(const std::vector<HDRI::raw_image> &image_files, const std::array<cv::Mat, 3UL> &curves,
+                        weight_function &&weighting, const std::vector<double> &expo) noexcept -> cv::Mat {
   // Size
   const auto width = image_files[0UL].get_width();
   const auto height = image_files[0UL].get_height();
@@ -21,26 +21,26 @@ cv::Mat construct_radiance(const std::vector<HDRI::raw_image> &image_files, cons
   // Radiance
   cv::Mat radiance(height, width, CV_32FC3);
 
-  for (auto idx = 0UL; idx < std::size(curves); ++idx) {  // r, g, b
-    for (auto y = 0UL; y < height; ++y) {
-      for (auto x = 0UL; x < width; ++x) {
-        double weighted_sum = 0.0;
-        double result = 0.0;
+  for (int idx = 0; idx < std::size(curves); ++idx) {  // r, g, b
+    for (auto y = 0; y < height; ++y) {
+      for (auto x = 0; x < width; ++x) {
+        auto weighted_sum = 0.0;
+        auto result = 0.0;
 
         // loop over all images
         for (auto k = 0UL; k < std::size(image_files); ++k) {
           const auto color = static_cast<int>(image_files[k].get_image_data().at<cv::Vec3b>(y, x)[idx]);
           const double w = std::invoke(std::forward<weight_function>(weighting), color);
 
-          result += static_cast<double>(w * (curves[idx].at<double>(color, 0) - std::log(expo[k])));
+          result += w * (curves[idx].at<double>(color, 0) - std::log(expo[k]));
           weighted_sum += w;
         }
 
         if (weighted_sum < std::numeric_limits<double>::epsilon() &&
             weighted_sum > -std::numeric_limits<double>::epsilon()) {  // near 0.0
-          radiance.at<cv::Vec3f>(y, x)[idx] = 0;
+          radiance.at<cv::Vec3f>(y, x)[idx] = 0.0F;
         } else {
-          radiance.at<cv::Vec3f>(y, x)[idx] = std::exp(result / weighted_sum);
+          radiance.at<cv::Vec3f>(y, x)[idx] = static_cast<float>(std::exp(result / weighted_sum));
         }
       }
     }
@@ -49,24 +49,24 @@ cv::Mat construct_radiance(const std::vector<HDRI::raw_image> &image_files, cons
   return radiance;
 }
 
-std::vector<cv::Mat> shrink_images(const std::vector<HDRI::raw_image> &input) noexcept {
+auto shrink_images(const std::vector<HDRI::raw_image> &input) noexcept -> std::vector<cv::Mat> {
   std::vector<cv::Mat> out;
   out.reserve(std::size(input));
 
-  constexpr size_t ratio = 50UL;
+  constexpr auto ratio = 50;
 
   for (const auto &img : input) {
     const auto &image_data = img.get_image_data();
 
-    size_t resized_col = image_data.cols / ratio;
-    size_t resized_row = image_data.rows / ratio;
+    auto resized_col = image_data.cols / ratio;
+    auto resized_row = image_data.rows / ratio;
 
-    if (resized_col < 15UL) {
-      resized_col = 15UL;
+    if (resized_col < 15) {
+      resized_col = 15;
     }
 
-    if (resized_row < 15UL) {
-      resized_row = 15UL;
+    if (resized_row < 15) {
+      resized_row = 15;
     }
 
     cv::Mat shrink_mat;
@@ -79,17 +79,17 @@ std::vector<cv::Mat> shrink_images(const std::vector<HDRI::raw_image> &input) no
   return out;
 }
 
-std::vector<std::vector<pixel>> generate_raw_pixel(const std::vector<cv::Mat> &shrink_mat) noexcept {
+auto generate_raw_pixel(const std::vector<cv::Mat> &shrink_mat) noexcept -> std::vector<std::vector<pixel>> {
   const auto width = shrink_mat[0UL].size().width;
   const auto height = shrink_mat[0UL].size().height;
 
   std::vector<std::vector<pixel>> pixels(shrink_mat.size());
 
   for (auto idx = 0UL; idx < shrink_mat.size(); ++idx) {
-    pixels[idx].resize(width * height);
+    pixels[idx].resize(static_cast<size_t>(width) * height);
 
-    for (auto y = 0UL; y < height; ++y) {
-      for (auto x = 0UL; x < width; ++x) {
+    for (auto y = 0; y < height; ++y) {
+      for (auto x = 0; x < width; ++x) {
         pixels[idx][y * width + x].b = shrink_mat[idx].at<cv::Vec3b>(y, x)[0UL];
         pixels[idx][y * width + x].g = shrink_mat[idx].at<cv::Vec3b>(y, x)[1UL];
         pixels[idx][y * width + x].r = shrink_mat[idx].at<cv::Vec3b>(y, x)[2UL];
@@ -100,8 +100,8 @@ std::vector<std::vector<pixel>> generate_raw_pixel(const std::vector<cv::Mat> &s
   return pixels;
 }
 
-std::array<std::vector<std::vector<int>>, 3UL> convert_to_z(const std::vector<std::vector<pixel>> &pixel,
-                                                            const size_t image_size, const size_t num_images) noexcept {
+auto convert_to_z(const std::vector<std::vector<pixel>> &pixel, const size_t image_size,
+                  const size_t num_images) noexcept -> std::array<std::vector<std::vector<int>>, 3UL> {
   std::array<std::vector<std::vector<int>>, 3UL> z_values;  // r, g, b
 
   for (auto &z_colors : z_values) {
@@ -141,12 +141,12 @@ hdr_image::hdr_image(const std::vector<raw_image> &raw_images) {
   compute_radiance(raw_images, exposure);
 }
 
-const std::array<cv::Mat, 3UL> &hdr_image::get_curves() const noexcept { return curves; }
+auto hdr_image::get_curves() const noexcept -> const std::array<cv::Mat, 3UL> & { return curves; }
 
 void hdr_image::compute_curves(const std::vector<HDRI::raw_image> &raw_images,
                                const std::vector<double> &exposure) noexcept {
   const auto shrink_mat = shrink_images(raw_images);
-  std::vector<std::vector<pixel>> raw_pixel = generate_raw_pixel(shrink_mat);
+  const auto raw_pixel = generate_raw_pixel(shrink_mat);
 
   // convert
   const auto z_values = convert_to_z(raw_pixel, shrink_mat[0UL].total(), shrink_mat.size());
@@ -171,6 +171,6 @@ void hdr_image::compute_radiance(const std::vector<HDRI::raw_image> &raw_images,
   radiance = construct_radiance(raw_images, curves, debevec_weight::get_weight, exposure);
 }
 
-const cv::Mat &hdr_image::get_radiance() const noexcept { return radiance; }
+auto hdr_image::get_radiance() const noexcept -> const cv::Mat & { return radiance; }
 
 }  // namespace HDRI
\ No newline at end of file
diff --git a/HDRI/main.cpp b/HDRI/main.cpp
index b1854be..81d0d7a 100644
--- a/HDRI/main.cpp
+++ b/HDRI/main.cpp
@@ -26,14 +26,15 @@ void output_curve(const cv::Mat &curve) noexcept {
 
   std::ofstream fout("out_curve.txt");
 
-  for (auto q = 0UL; q < height; ++q) {
-    for (auto p = 0UL; p < width; ++p) {
+  for (auto q = 0; q < height; ++q) {
+    for (auto p = 0; p < width; ++p) {
       fout << curve.at<double>(q, p) << std::endl;
     }
   }
 }
 
-std::vector<HDRI::raw_image> load_raw_images(const std::string &base_path, const std::string &file_name) noexcept {
+auto load_raw_images(const std::string &base_path, const std::string &file_name) noexcept
+    -> std::vector<HDRI::raw_image> {
   const auto full_path = base_path + file_name;
 
   std::ifstream input(full_path);
@@ -93,7 +94,7 @@ std::vector<HDRI::raw_image> load_raw_images(const std::string &base_path, const
 
 }  // namespace
 
-int main(int argc, char *argv[]) {
+auto main(int argc, char *argv[]) -> int {
   constexpr auto default_base_path{"../InputImage/"};
   constexpr auto default_files{"list.txt"};
 
diff --git a/HDRI/raw_image.cpp b/HDRI/raw_image.cpp
index bdc1baf..f52d308 100644
--- a/HDRI/raw_image.cpp
+++ b/HDRI/raw_image.cpp
@@ -5,8 +5,8 @@
 
 namespace HDRI {
 
-raw_image::raw_image(std::string file_name, const double shutter_speed)
-    : image_data{cv::imread(file_name)}, expo{1.0 / shutter_speed}, name{std::move(file_name)} {
+raw_image::raw_image(const std::string& file_name, const double shutter_speed)
+    : image_data{cv::imread(file_name)}, expo{1.0 / shutter_speed} {
   if (image_data.empty()) {
     std::cerr << "Fail to load: " + file_name << std::endl;
     throw std::runtime_error("Fail to load" + file_name);
diff --git a/HDRI/raw_image.hpp b/HDRI/raw_image.hpp
index c1d5998..f5ac676 100644
--- a/HDRI/raw_image.hpp
+++ b/HDRI/raw_image.hpp
@@ -8,7 +8,7 @@ namespace HDRI {
 
 class raw_image final {
  public:
-  explicit raw_image(std::string file_name, const double shutter_speed);
+  explicit raw_image(const std::string &file_name, const double shutter_speed);
 
   raw_image(const raw_image &) noexcept = default;
   raw_image(raw_image &&) noexcept = default;
@@ -27,7 +27,6 @@ class raw_image final {
 
  private:
   cv::Mat image_data;
-  std::string name;
   double expo;
 };
 
diff --git a/HDRI/tone_map_algo.cpp b/HDRI/tone_map_algo.cpp
index c549dfe..1e1bf26 100644
--- a/HDRI/tone_map_algo.cpp
+++ b/HDRI/tone_map_algo.cpp
@@ -4,8 +4,8 @@
 
 namespace {
 
-constexpr float rgb_to_luminance(const float r, const float g, const float b) noexcept {
-  return 0.2126f * r + 0.7152f * g + 0.0722f * b;
+constexpr auto rgb_to_luminance(const float r, const float g, const float b) noexcept -> float {
+  return 0.2126F * r + 0.7152F * g + 0.0722F * b;
 }
 
 }  // namespace
@@ -13,47 +13,47 @@ constexpr float rgb_to_luminance(const float r, const float g, const float b) no
 namespace HDRI {
 
 auto reinhard_tone_map_algo(const cv::Mat &input_radiance) noexcept -> cv::Mat {
-  constexpr float epsilon = 0.00001f;
-  constexpr float a = 0.18f;  // from paper
+  constexpr auto epsilon = 0.00001F;
+  constexpr auto a = 0.18F;  // from paper
 
   // color space transform
   cv::Mat lumi(input_radiance.size(), CV_32FC1);
-  for (auto y = 0U; y < input_radiance.size().height; ++y) {
-    for (auto x = 0U; x < input_radiance.size().width; ++x) {
+  for (auto y = 0; y < input_radiance.size().height; ++y) {
+    for (auto x = 0; x < input_radiance.size().width; ++x) {
       lumi.at<float>(y, x) =
           rgb_to_luminance(input_radiance.at<cv::Vec3f>(y, x)[2], input_radiance.at<cv::Vec3f>(y, x)[1],
                            input_radiance.at<cv::Vec3f>(y, x)[0]);
     }
   }
 
-  double Lw_bar = 0.0;
+  auto Lw_bar = 0.0F;
 
   // loop over all values in the Mat
-  for (auto y = 0U; y < input_radiance.size().height; ++y) {
-    for (auto x = 0U; x < input_radiance.size().width; ++x) {
+  for (auto y = 0; y < input_radiance.size().height; ++y) {
+    for (auto x = 0; x < input_radiance.size().width; ++x) {
       Lw_bar += std::log(lumi.at<float>(y, x) + epsilon);  // from paper
     }
   }
 
   std::cerr << "Lw_bar: " << Lw_bar << std::endl;
 
-  const size_t N = input_radiance.total();
+  const auto N = static_cast<float>(input_radiance.total());
 
   // Equation 1 in the paper is wrong. The division by N should be placed
   // before the summation, not outside the exponentiation.
   Lw_bar = std::exp(Lw_bar / N);
 
-  const float coeff = a / Lw_bar;
+  const auto coeff = a / Lw_bar;
 
-  const float L_white = 1.7f;  // test
+  const auto L_white = 1.7F;  // test
 
   // compute Ld
   cv::Mat Ld(input_radiance.size(), CV_32FC1);
 
   for (auto y = 0; y < input_radiance.size().height; ++y) {
     for (auto x = 0; x < input_radiance.size().width; ++x) {
-      float L = coeff * lumi.at<float>(y, x);  // Ld = (a / Lw_bar ) * (Lw(x,y))
-      Ld.at<float>(y, x) = L * (1.0f + L / (L_white * L_white)) / (1.0f + L);
+      auto L = coeff * lumi.at<float>(y, x);  // Ld = (a / Lw_bar ) * (Lw(x,y))
+      Ld.at<float>(y, x) = L * (1.0F + L / (L_white * L_white)) / (1.0F + L);
 
       if (L > L_white) {
         Ld.at<float>(y, x) = 1;
@@ -62,7 +62,7 @@ auto reinhard_tone_map_algo(const cv::Mat &input_radiance) noexcept -> cv::Mat {
   }
 
   cv::Mat output_image(input_radiance.size(), CV_8UC3);
-  for (auto idx = 0U; idx < 3U; ++idx) {  // rgb
+  for (auto idx = 0; idx < 3; ++idx) {  // rgb
     for (auto y = 0; y < input_radiance.size().height; ++y) {
       for (auto x = 0; x < input_radiance.size().width; ++x) {
         output_image.at<cv::Vec3b>(y, x)[idx] = cv::saturate_cast<uchar>(