Compute lambda_shot and lambda_read

include/hdrplus/merge.h

@@ -10,6 +10,9 @@ namespace hdrplus
 class merge
 {
     public:
+        float baseline_lambda_shot = 3.24 * pow( 10, -4 );
+        float baseline_lambda_read = 4.3 * pow( 10, -6 );
+
         merge() = default;
         ~merge() = default;
 
@@ -26,6 +29,11 @@ class merge
                       int ISO, \
                       int white_level, \
                       double black_level );
+    
+    private:
+        std::pair<double, double> getNoiseParams( int ISO, \
+                      int white_level, \
+                      double black_level );
 };
 
 } // namespace hdrplus

src/merge.cpp

@@ -1,5 +1,6 @@
 #include <opencv2/opencv.hpp> // all opencv header
 #include <vector>
+#include <utility>
 #include "hdrplus/merge.h"
 #include "hdrplus/burst.h"
 
@@ -12,7 +13,29 @@ void merge::process( const hdrplus::burst& burst_images, \
                      int white_level, \
                      double black_level )
 {
+    double lambda_shot, lambda_read;
+    std::tie(lambda_shot, lambda_read) = merge::getNoiseParams(ISO, white_level, black_level);
+
     
 }
 
+std::pair<double, double> merge::getNoiseParams( int ISO, \
+                                          int white_level, \
+                                          double black_level ) 
+{
+    // Set ISO to 100 if not positive
+    ISO = ISO <= 0 ? 100 : ISO;
+
+    // Calculate shot noise and read noise parameters w.r.t ISO 100
+    double lambda_shot_p = ISO / 100.0f * baseline_lambda_shot;
+	double lambda_read_p = (ISO / 100.0f) * (ISO / 100.0f) * baseline_lambda_read;
+
+    // Rescale shot and read noise to normal range
+    double lambda_shot = lambda_shot_p * (white_level - black_level);
+    double lambda_read = lambda_read_p * (white_level - black_level) * (white_level - black_level);
+
+    // return pair
+    return std::make_pair(lambda_shot, lambda_read);
+}
+
 } // namespace hdrplus