Update compensation of aperture and ISO change in HDR fusion

src/aliceVision/sfmData/View.cpp

@@ -17,18 +17,45 @@
 namespace aliceVision {
 namespace sfmData {
 
-float View::getCameraExposureSetting() const
+float View::getCameraExposureSetting(const float referenceISO, const float referenceFNumber) const
 {
     const float shutter = getMetadataShutter();
     const float fnumber = getMetadataFNumber();
+    const float iso = getMetadataISO();
+
     if(shutter < 0 || fnumber < 0)
         return -1.f;
 
-    const float iso = getMetadataISO();
-    const float isoRatio = (iso < 0.f) ? 1.0 : (iso / 100.f);
+    float lReferenceIso = referenceISO;
+    if (lReferenceIso < 0.0f) {
+        lReferenceIso = iso;
+    }
 
-    float cameraExposure = (shutter * isoRatio) / (fnumber * fnumber);
-    return cameraExposure;
+    float lReferenceFNumber = referenceFNumber;
+    if (lReferenceFNumber < 0.0f) {
+        lReferenceFNumber = fnumber;
+    }
+
+    /* 
+    iso = qLt / aperture^2
+    isoratio = iso2 / iso1 = qLt / aperture1² / (qLt / aperture2²) 
+    isoratio = aperture2² / aperture1²
+    aperture2² = iso2 / iso1 * 1
+    aperture2 = sqrt(iso2 / iso1)
+    */
+    float iso_2_aperture = sqrt(iso / lReferenceIso);
+
+    /*
+    aperture = f / diameter
+    aperture2 / aperture1 = diameter2 / diameter1
+    (aperture2 / aperture1)² = (area2 / pi) / (area1 / pi)
+    */
+
+    float new_fnumber = fnumber * iso_2_aperture;
+    float exp_increase = (new_fnumber / lReferenceFNumber) * (new_fnumber / lReferenceFNumber);
+
+
+    return shutter * exp_increase;
 }
 
 float View::getEv() const

src/aliceVision/sfmData/View.hpp

@@ -207,7 +207,7 @@ class View
    * For the same scene, this value is linearly proportional to the amount of light captured by the camera according to
    * the shooting parameters (shutter speed, f-number, iso).
    */
-  float getCameraExposureSetting() const;
+  float getCameraExposureSetting(const float referenceISO = -1.0f, const float referenceFNumber = -1.0f) const;
 
   /**
    * @brief Get the Exposure Value. EV is a number that represents a combination of a camera's shutter speed and

src/software/pipeline/main_LdrToHdrCalibration.cpp

@@ -353,8 +353,9 @@ int aliceVision_main(int argc, char** argv)
         std::vector<float> exposures;
 
         for(int j = 0; j < group.size(); ++j)
-        {
-            float etime = group[j]->getCameraExposureSetting();
+        {   
+
+            float etime = group[j]->getCameraExposureSetting(group[0]->getMetadataISO(), group[0]->getMetadataFNumber());
             exposures.push_back(etime);
         }
         groupedExposures.push_back(exposures);

src/software/pipeline/main_LdrToHdrMerge.cpp

@@ -261,7 +261,7 @@ int aliceVision_main(int argc, char** argv)
             ALICEVISION_LOG_INFO("Load " << filepath);
             image::readImage(filepath, images[i], image::EImageColorSpace::SRGB);
 
-            exposures[i] = group[i]->getCameraExposureSetting();
+            exposures[i] = group[i]->getCameraExposureSetting(targetView->getMetadataISO(), targetView->getMetadataFNumber());
         }
 
         // Merge HDR images