diff --git a/rawimage.cpp b/rawimage.cpp
index 7d4e954..a35be38 100644
--- a/rawimage.cpp
+++ b/rawimage.cpp
@@ -231,6 +231,56 @@ void calcStats(const T *data, size_t n, size_t w, RawImage::Stats &stats)
         }
     }
 
+    if constexpr(std::is_floating_point_v<T>)
+    {
+        T mmin = *std::min_element(min, min + 4);
+        T mmax = *std::max_element(max, max + 4);
+        for(int i=0; i<4; i++)
+        {
+            histogram[i].clear();
+            histogram[i].resize(histSize, 0);
+        }
+
+        T a = 1.0 / (mmax - mmin);
+        T b = -mmin / (mmax - mmin);
+
+        auto histFunc = [&](T d, int x)
+        {
+            uint16_t idx = std::clamp((T)(d * a + b) * histSize, (T)0.0, (T)65535.0);
+            histogram[x][idx]++;
+        };
+
+        // calculate histogram again
+        if(mmin < 0.0 || mmax > 1.0)
+        {
+            for(size_t i = 0; i < n; i++)
+            {
+                histFunc(data[i*ch], 0);
+                if constexpr(ch >= 3)
+                {
+                    histFunc(data[i*ch + 1], 1);
+                    histFunc(data[i*ch + 2], 2);
+                }
+            }
+
+            if constexpr(ch == 1)
+            {
+                size_t h = (n / w) & (SIZE_MAX-1);
+                w &= (SIZE_MAX-1);
+                for(size_t y=0; y<h; y+=2)
+                {
+                    for(size_t x=0; x<w; x+=2)
+                    {
+                        histFunc(data[y*w+x], 1);
+                        histFunc(data[y*w+x+1], 2);
+                        histFunc(data[(y+1)*w+x], 2);
+                        histFunc(data[(y+1)*w+x+1], 3);
+                    }
+                }
+            }
+        }
+    }
+
     for(int i = 0; i < 4; i++)
     {
         stats.m_min[i] = min[i];
@@ -824,7 +874,7 @@ std::pair<float, float> RawImage::unitScale() const
     }
 
     if(min < 0.0f || max > 1.0f)
-        return {1.0f / (max - min), min / (max - min)};
+        return {1.0f / (max - min), -min / (max - min)};
     else
         return {1.0f, 0.0f};
 }
@@ -1112,11 +1162,14 @@ void RawImage::applySTF(const MTFParam &mtfParams)
         if constexpr(std::numeric_limits<std::remove_reference_t<decltype(*src)>>::is_integer)
             s = (float)std::numeric_limits<std::remove_reference_t<decltype(*src)>>::max();
 
+        auto unit = unitScale();
         float iscale = 1.0f / s;
         size_t len = size() * m_ch;
         for(size_t i = 0; i < len; i++)
         {
-            float x = src[i] * iscale;
+            float x;
+            if constexpr(std::numeric_limits<std::remove_reference_t<decltype(*src)>>::is_integer)x = src[i] * iscale;
+            else x = src[i] * unit.first + unit.second;
             x = (x - mtfParams.blackPoint[0]) / (mtfParams.whitePoint[0] - mtfParams.blackPoint[0]);
             x = std::clamp(x, 0.0f, 1.0f);
             x = ((mtfParams.midPoint[0] - 1.0f) * x) / ((2.0f * mtfParams.midPoint[0] - 1.0f) * x - mtfParams.midPoint[0]);