diff --git a/stretchtoolbar.cpp b/stretchtoolbar.cpp
index 1373047..88adc93 100644
--- a/stretchtoolbar.cpp
+++ b/stretchtoolbar.cpp
@@ -120,12 +120,15 @@ void StretchToolbar::stretchImage(Image *img)
             mad = stats.m_mad[i];
             max = stats.m_max[i];
             median /= img->rawImage()->norm();
+            bool a = median > 0.5 ? true : false;
             mad /= img->rawImage()->norm();
-            max /= img->rawImage()->norm();
-            float bp = median + mad * BLACK_POINT_SIGMA * MAD_TO_SIGMA;
-            float mid = MTF(median - bp, TARGET_BACKGROUND);
+            max = 1.0f;// /= img->rawImage()->norm();
+            float bp = a || mad == 0.0f ? 0.0f : std::clamp(median + mad * BLACK_POINT_SIGMA * MAD_TO_SIGMA, 0.0, 1.0);
+            if(a && mad != 0.0f)
+                max = std::clamp(median - mad * BLACK_POINT_SIGMA * MAD_TO_SIGMA, 0.0, 1.0);
+            float mid = !a ? MTF(median - bp, TARGET_BACKGROUND) : MTF(TARGET_BACKGROUND, max - median);
             m_mtfParam.blackPoint[i-o] = bp;
-            m_mtfParam.midPoint[i-o] = mid / max;
+            m_mtfParam.midPoint[i-o] = mid;// / max;
             m_mtfParam.whitePoint[i-o] = max;
             bp2 += bp;
             mid2 += mid;