Merge pull request #30719 from pbkx:port-tonemap-reinhard-intensity-5x

photo: preserve TonemapReinhard intensity during processing

modules/photo/src/tonemap.cpp

@@ -233,7 +233,7 @@ public:
 
         float key = (log_max - log_mean) / (log_max - log_min);
         float map_key = 0.3f + 0.7f * std::pow(key, 1.4f);
-        intensity = exp(-intensity);
+        const float intensity_scale = exp(-intensity);
         Scalar chan_mean = mean(img);
         float gray_mean = static_cast<float>(mean(gray_img)[0]);
 
@@ -244,7 +244,7 @@ public:
             float global = color_adapt * static_cast<float>(chan_mean[i]) + (1.0f - color_adapt) * gray_mean;
             Mat adapt = color_adapt * channels[i] + (1.0f - color_adapt) * gray_img;
             adapt = light_adapt * adapt + (1.0f - light_adapt) * global;
-            pow(intensity * adapt, map_key, adapt);
+            pow(intensity_scale * adapt, map_key, adapt);
             channels[i] = channels[i].mul(1.0f / (adapt + channels[i]));
         }
         gray_img.release();

modules/photo/test/test_hdr.cpp

@@ -118,6 +118,27 @@ TEST(Photo_Tonemap, regression)
     checkEqual(result, expected, 3, "Mantiuk");
 }
 
+TEST(Photo_Tonemap, reinhard_preserves_intensity)
+{
+    string test_path = string(cvtest::TS::ptr()->get_data_path()) + "hdr/tonemap/";
+
+    Mat img, first, second;
+    loadImage(test_path + "image.hdr", img);
+    Mat original = img.clone();
+
+    Ptr<TonemapReinhard> tonemap = createTonemapReinhard(1.0f, 0.0f, 1.0f, 0.0f);
+    EXPECT_FLOAT_EQ(0.0f, tonemap->getIntensity());
+
+    tonemap->process(img, first);
+    EXPECT_FLOAT_EQ(0.0f, tonemap->getIntensity());
+
+    tonemap->process(img, second);
+    EXPECT_FLOAT_EQ(0.0f, tonemap->getIntensity());
+
+    checkEqual(first, second, 0, "Reinhard repeated process");
+    checkEqual(img, original, 0, "Reinhard input preservation");
+}
+
 TEST(Photo_AlignMTB, regression)
 {
     const int TESTS_COUNT = 100;