Correct images exposure in PrepareDenseScene

add methods in sfmData to calculate exposure values + correct them during the PrepareDenseScene

src/aliceVision/sfmData/SfMData.hpp

@@ -297,6 +297,26 @@ class SfMData
     return _rigs.at(view.getRigId());
   }
 
+  /**
+   * @brief Get the median Exposure Value (Ev) of
+   * @return
+   */
+
+  float getMedianEv() const
+  {
+      std::vector<float> evList;
+      evList.reserve(views.size());
+
+      for(const auto& view : views)
+      {
+          float ev = view.second->getEv();
+          evList.emplace_back(ev);
+      }
+      std::nth_element(evList.begin(), evList.begin() + evList.size()/2, evList.end());
+      float evMedian = evList[evList.size()/2];
+      return evMedian;
+  }
+
   /**
    * @brief Add the given \p folder to features folders.
    * @note If SfmData's absolutePath has been set, 

src/aliceVision/sfmData/View.hpp

@@ -191,6 +191,37 @@ class View
     return (!isPartOfRig() || _isIndependantPose);
   }
 
+  float getEv() const
+  {
+      const float shutter = getMetadataShutter();
+      const float aperture = getMetadataAperture();
+      const float iso = static_cast<float>(getMetadataISO());
+
+      if(shutter < 0 || aperture < 0 || iso < 0)
+          return -1;
+
+      // WIKIPEDIA : + log2f(iso/100.f)
+      float ev = log2f(std::pow(aperture, 2.0f) / shutter) - log2f(iso/100.f);
+      return ev;
+  }
+
+  /**
+   * @brief Get the value of the gap bewteen the view's exposition and a reference exposition
+   * @param [refEv] the median exposition of all views
+   * @return the exposure compensation
+   */
+  float getEvCompensation(float refEv) const
+  {
+      float evComp = 1.0f;
+      float comp = getEv() - refEv;
+
+      if(getEv() != -1)
+          evComp = std::pow(2.0f, comp);
+
+      return evComp;
+  }
+
+
   /**
    * @brief Return true if the given metadata name exists
    * @param[in] name The metadata name
@@ -319,6 +350,39 @@ class View
     return -1;
   }
 
+  /**
+     * @brief Get the corresponding "ExposureTime" (shutter) metadata value
+     * @return the metadata value float or -1 if no corresponding value
+     */
+  float getMetadataShutter() const
+  {
+      if(hasDigitMetadata("ExposureTime"))
+          return std::stof(getMetadata("ExposureTime"));
+      return -1;
+  }
+
+  /**
+     * @brief Get the corresponding "FNumber" (aperture) metadata value
+     * @return the metadata value float or -1 if no corresponding value
+     */
+  float getMetadataAperture() const
+  {
+      if(hasDigitMetadata("FNumber"))
+          return std::stof(getMetadata("FNumber"));
+      return -1;
+  }
+
+  /**
+     * @brief Get the corresponding "PhotographicSensitivity" (ISO) metadata value
+     * @return the metadata value int or -1 if no corresponding value
+     */
+  float getMetadataISO() const
+  {
+      if(hasDigitMetadata("Exif:PhotographicSensitivity"))
+          return std::stoi(getMetadata("Exif:PhotographicSensitivity"));
+      return -1;
+  }
+
   /**
    * @brief Get the corresponding "Orientation" metadata value
    * @return the enum EEXIFOrientation

src/software/pipeline/main_prepareDenseScene.cpp

@@ -44,7 +44,8 @@ bool prepareDenseScene(const SfMData& sfmData,
                        const std::string& outFolder,
                        image::EImageFileType outputFileType,
                        bool saveMetadata,
-                       bool saveMatricesFiles)
+                       bool saveMatricesFiles,
+                       bool evCorrection)
 {
   // defined view Ids
   std::set<IndexT> viewIds;
@@ -76,6 +77,10 @@ bool prepareDenseScene(const SfMData& sfmData,
   // export data
   boost::progress_display progressBar(viewIds.size(), std::cout, "Exporting Scene Undistorted Images\n");
 
+  // for exposure correction
+  const float medianEv = sfmData.getMedianEv();
+  ALICEVISION_LOG_INFO("median Ev : " << medianEv);
+
 #pragma omp parallel for num_threads(3)
   for(int i = 0; i < viewIds.size(); ++i)
   {
@@ -188,6 +193,22 @@ bool prepareDenseScene(const SfMData& sfmData,
       Image<RGBfColor> image, image_ud;
 
       readImage(srcImage, image, image::EImageColorSpace::LINEAR);
+
+      //exposure correction
+      if(evCorrection)
+      {
+          float exposureCompensation = view->getEvCompensation(medianEv);
+
+          //metadata & log
+          metadata.push_back(oiio::ParamValue("AliceVision:EV", view->getEv()));
+          metadata.push_back(oiio::ParamValue("AliceVision:EVComp", exposureCompensation));
+          ALICEVISION_LOG_INFO("image " + std::to_string(viewId) + " Ev : " + std::to_string(view->getEv()));
+          ALICEVISION_LOG_INFO("image " + std::to_string(viewId) + " Ev compensation : " + std::to_string(exposureCompensation));
+
+          for(int pix = 0; pix < image.Width() * image.Height(); ++pix)
+              image(pix) = image(pix) * exposureCompensation;
+
+      }
 
       // undistort
       if(cam->isValid() && cam->have_disto())
@@ -222,6 +243,7 @@ int main(int argc, char *argv[])
   int rangeSize = 1;
   bool saveMetadata = true;
   bool saveMatricesTxtFiles = false;
+  bool evCorrection = false;
 
   po::options_description allParams("AliceVision prepareDenseScene");
 
@@ -246,7 +268,9 @@ int main(int argc, char *argv[])
     ("rangeStart", po::value<int>(&rangeStart)->default_value(rangeStart),
       "Range image index start.")
     ("rangeSize", po::value<int>(&rangeSize)->default_value(rangeSize),
-      "Range size.");
+      "Range size.")
+    ("evCorrection", po::value<bool>(&evCorrection)->default_value(evCorrection),
+      "Correct exposure value.");
 
   po::options_description logParams("Log parameters");
   logParams.add_options()
@@ -324,7 +348,7 @@ int main(int argc, char *argv[])
   }
 
   // export
-  if(prepareDenseScene(sfmData, imagesFolders, rangeStart, rangeEnd, outFolder, outputFileType, saveMetadata, saveMatricesTxtFiles))
+  if(prepareDenseScene(sfmData, imagesFolders, rangeStart, rangeEnd, outFolder, outputFileType, saveMetadata, saveMatricesTxtFiles, evCorrection))
     return EXIT_SUCCESS;
 
   return EXIT_FAILURE;