--- a/Core/ImageFormats/ImageProcessing.cpp	Wed Jul 02 13:53:56 2014 +0200
+++ b/Core/ImageFormats/ImageProcessing.cpp	Wed Jul 02 14:41:57 2014 +0200
@@ -75,6 +75,44 @@
   }
 
 
+  template <typename TargetType>
+  static void ConvertColorToGrayscale(ImageAccessor& target,
+                              const ImageAccessor& source)
+  {
+    assert(source.GetFormat() == PixelFormat_RGB24);
+
+    const TargetType minValue = std::numeric_limits<TargetType>::min();
+    const TargetType maxValue = std::numeric_limits<TargetType>::max();
+
+    for (unsigned int y = 0; y < source.GetHeight(); y++)
+    {
+      TargetType* t = reinterpret_cast<TargetType*>(target.GetRow(y));
+      const uint8_t* s = reinterpret_cast<const uint8_t*>(source.GetConstRow(y));
+
+      for (unsigned int x = 0; x < source.GetWidth(); x++, t++, s += 3)
+      {
+        // Y = 0.2126 R + 0.7152 G + 0.0722 B
+        int32_t v = (2126 * static_cast<int32_t>(s[0]) +
+                     7152 * static_cast<int32_t>(s[1]) +
+                     0722 * static_cast<int32_t>(s[2])) / 1000;
+        
+        if (static_cast<int32_t>(v) < static_cast<int32_t>(minValue))
+        {
+          *t = minValue;
+        }
+        else if (static_cast<int32_t>(v) > static_cast<int32_t>(maxValue))
+        {
+          *t = maxValue;
+        }
+        else
+        {
+          *t = static_cast<TargetType>(v);
+        }
+      }
+    }
+  }
+
+
   template <typename PixelType>
   static void SetInternal(ImageAccessor& image,
                           int64_t constant)
@@ -319,6 +357,27 @@
       return;
     }
 
+    if (target.GetFormat() == PixelFormat_Grayscale8 &&
+        source.GetFormat() == PixelFormat_RGB24)
+    {
+      ConvertColorToGrayscale<uint8_t>(target, source);
+      return;
+    }
+
+    if (target.GetFormat() == PixelFormat_Grayscale16 &&
+        source.GetFormat() == PixelFormat_RGB24)
+    {
+      ConvertColorToGrayscale<uint16_t>(target, source);
+      return;
+    }
+
+    if (target.GetFormat() == PixelFormat_SignedGrayscale16 &&
+        source.GetFormat() == PixelFormat_RGB24)
+    {
+      ConvertColorToGrayscale<int16_t>(target, source);
+      return;
+    }
+
     throw OrthancException(ErrorCode_NotImplemented);
   }