diff --git a/rtengine/pixelshift.cc b/rtengine/pixelshift.cc
index c5ead46c3..2d808bb2e 100644
--- a/rtengine/pixelshift.cc
+++ b/rtengine/pixelshift.cc
@@ -110,7 +110,7 @@ float nonGreenDiffCross(float a, float b, float c, float d, float centre, float
     if(!showMotion) {
         return result;
     } else if(result > 0.f) { // for the motion mask
-        return std::fabs(a - b) / (std::max(a, b) + 0.01f);
+        return std::sqrt((result / (stddev + result + 0.01f))); //1.f; //std::fabs(a - b) / (std::max(a, b) + 0.01f);
     } else {
         return 0.f;
     }