Fixed the formula to compute the well-exposedness weight map.

modules/photo/src/merge.cpp

@@ -194,10 +194,11 @@ public:
 
             wellexp = Mat::ones(size, CV_32F);
             for(int c = 0; c < channels; c++) {
-                Mat exp = splitted[c] - 0.5f;
-                pow(exp, 2.0f, exp);
-                exp = -exp / 0.08f;
-                wellexp = wellexp.mul(exp);
+                Mat expo = splitted[c] - 0.5f;
+                pow(expo, 2.0f, expo);
+                expo = -expo / 0.08f;
+                exp(expo, expo);
+                wellexp = wellexp.mul(expo);
             }
 
             pow(contrast, wcon, contrast);