diff --git a/Modules/MitkExt/Algorithms/mitkSimpleHistogram.cpp b/Modules/MitkExt/Algorithms/mitkSimpleHistogram.cpp
index 9806be62e4..72d6e6bc60 100644
--- a/Modules/MitkExt/Algorithms/mitkSimpleHistogram.cpp
+++ b/Modules/MitkExt/Algorithms/mitkSimpleHistogram.cpp
@@ -1,234 +1,244 @@
 /*=========================================================================
 
 Program:   Medical Imaging & Interaction Toolkit
 Language:  C++
 Date:      $Date$
 Version:   $Revision$
 
 Copyright (c) German Cancer Research Center, Division of Medical and
 Biological Informatics. All rights reserved.
 See MITKCopyright.txt or http://www.mitk.org/copyright.html for details.
 
 This software is distributed WITHOUT ANY WARRANTY; without even
 the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 PURPOSE.  See the above copyright notices for more information.
 
 =========================================================================*/
 
 #include "mitkSimpleHistogram.h"
 
 #include "mitkSimpleUnstructuredGridHistogram.h"
 #include "mitkUnstructuredGrid.h"
 
 namespace mitk {
 
 void SimpleImageHistogram::ComputeFromBaseData( BaseData* src )
 {
   valid = false;
 
+  //check if input is valid
+  if (src==NULL) return;
   Image* source = dynamic_cast<Image*>(src);
+  if (source==NULL) return;
+  else if (source->IsEmpty()) return;
+
+  
 
   // dummy histogram
   {
     min=0;
     max=1;
     first=0;
     last=1;
   }
 
    {
     int typInt=0;
     {
       const std::type_info* typ=source->GetPixelType().GetTypeId();
       if     (*typ == typeid(unsigned char )) typInt=0;
       else if(*typ == typeid(signed char   )) typInt=1;
       else if(*typ == typeid(unsigned short)) typInt=2;
       else if(*typ == typeid(signed short  )) typInt=3;
       else
       {
         MITK_WARN << "SimpleImageHistogram currently only supports un/signed char/short";
         return;
       }
     }
 
 
     first=-32768;  last=65535; // support at least full signed and unsigned short range
 
     if(histogram)
       delete histogram;
 
     histogram = new CountType[last-first+1];
     memset(histogram,0,sizeof(CountType)*(last-first+1));
     highest = 0;
     max = first - 1;
     min = last + 1;
 
     unsigned int num=1;
     for(unsigned int r=0;r<source->GetDimension();r++)
       num*=source->GetDimension(r);
 
    // MITK_INFO << "building histogramm of integer image: 0=" << source->GetDimension(0) << " 1=" << source->GetDimension(1) << " 2=" << source->GetDimension(2) << " 3=" <<  source->GetDimension(3);
 
     void *src=source->GetData();
 
     do
     {
       int value;
 
       switch(typInt)
       {
         case 0: { unsigned char  *t=(unsigned char *)src; value=*t++; src=(void*)t; } break;
         case 1: {   signed char  *t=(  signed char *)src; value=*t++; src=(void*)t; } break;
         case 2: { unsigned short *t=(unsigned short*)src; value=*t++; src=(void*)t; } break;
         case 3: {   signed short *t=(  signed short*)src; value=*t++; src=(void*)t; } break;
       }
 
       if(value >= first && value <= last)
       {
         if(value < min) min = value;
         if(value > max) max = value;
         CountType tmp = ++histogram[value-first];
         if(tmp > highest) highest = tmp;
       }
     }
     while(--num);
 
     MITK_INFO << "histogramm computed: min=" << min << " max=" << max << " highestBin=" << highest << " samples=" << num;
   }
 
   invLogHighest = 1.0/log(double(highest));
   valid = true;
 }
 
+bool SimpleImageHistogram::GetValid()
+  {
+  return valid;
+  }
 
 float SimpleImageHistogram::GetRelativeBin( double left, double right ) const
 {
   if( !valid )
     return 0.0f;
 
   int iLeft = floorf(left);
   int iRight = ceilf(right);
 
  /*
   double sum = 0;
 
   for( int r = 0 ; r < 256 ; r++)
   {
     int pos = left + (right-left) * r/255.0;
     int posInArray = floorf(pos+0.5f) - first;
     sum += float(log(double(histogram[posInArray])));
   }
 
   sum /= 256.0;
   return float(sum*invLogHighest);
  */
 
   CountType maximum = 0;
 
   for( int i = iLeft; i <= iRight ; i++)
   {
     int posInArray = i - first;
     if( histogram[posInArray] > maximum ) maximum = histogram[posInArray];
   }
 
   return float(log(double(maximum))*invLogHighest);
 }
 
 class ImageHistogramCacheElement : public SimpleHistogramCache::Element
 {
   public:
 
     void ComputeFromBaseData(BaseData* baseData)
     {
       histogram.ComputeFromBaseData(baseData);
     }
 
     SimpleHistogram* GetHistogram()
     {
       return &histogram;
     }
 
     SimpleImageHistogram histogram;
 };
 
 class UnstructuredGridHistogramCacheElement : public SimpleHistogramCache::Element
 {
   public:
 
     void ComputeFromBaseData(BaseData* baseData)
     {
       histogram.ComputeFromBaseData(baseData);
     }
 
     SimpleHistogram* GetHistogram()
     {
       return &histogram;
     }
 
     SimpleUnstructuredGridHistogram histogram;
 };
 
 SimpleHistogram* SimpleHistogramCache::operator[](BaseData::Pointer sp_BaseData)
 {
   BaseData *p_BaseData = sp_BaseData.GetPointer();
 
   if(!p_BaseData)
   {
     MITK_WARN << "SimpleHistogramCache::operator[] with null base data called";
     return 0;
   }
 
   Element *elementToUpdate = 0;
 
   bool first = true;
 
   for(CacheContainer::iterator iter = cache.begin(); iter != cache.end(); iter++)
   {
     Element *e = *iter;
     BaseData *p_tmp = e->baseData.GetPointer();
 
     if(p_tmp == p_BaseData)
     {
       if(!first)
       {
         cache.erase(iter);
         cache.push_front(e);
       }
       if( p_BaseData->GetMTime() > e->m_LastUpdateTime.GetMTime())
         goto recomputeElement;
 
       //MITK_INFO << "using a cached histogram";
 
       return e->GetHistogram();
     }
 
     first = false;
   }
 
   if (dynamic_cast<Image*>(p_BaseData))
   {
     elementToUpdate = new ImageHistogramCacheElement();
   }
   else if (dynamic_cast<UnstructuredGrid*>(p_BaseData))
   {
     elementToUpdate = new UnstructuredGridHistogramCacheElement();
   }
   else
   {
     MITK_WARN << "not supported: " << p_BaseData->GetNameOfClass();
   }
 
   elementToUpdate->baseData = p_BaseData;
   cache.push_front(elementToUpdate);
   TrimCache();
 
   recomputeElement:
 
   //MITK_INFO << "computing a new histogram";
 
   elementToUpdate->ComputeFromBaseData(p_BaseData);
   elementToUpdate->m_LastUpdateTime.Modified();
   return elementToUpdate->GetHistogram();
 }
 
 }
diff --git a/Modules/MitkExt/Algorithms/mitkSimpleHistogram.h b/Modules/MitkExt/Algorithms/mitkSimpleHistogram.h
index c07919851c..1c2b92ec7a 100644
--- a/Modules/MitkExt/Algorithms/mitkSimpleHistogram.h
+++ b/Modules/MitkExt/Algorithms/mitkSimpleHistogram.h
@@ -1,162 +1,166 @@
 /*=========================================================================
 
 Program:   Medical Imaging & Interaction Toolkit
 Language:  C++
 Date:      $Date$
 Version:   $Revision$
 
 Copyright (c) German Cancer Research Center, Division of Medical and
 Biological Informatics. All rights reserved.
 See MITKCopyright.txt or http://www.mitk.org/copyright.html for details.
 
 This software is distributed WITHOUT ANY WARRANTY; without even
 the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 PURPOSE.  See the above copyright notices for more information.
 
 =========================================================================*/
 
 
 #ifndef MITKSIMPLEHISTOGRAM_H
 #define MITKSIMPLEHISTOGRAM_H
 
 #include "MitkExtExports.h"
 
 #include <mitkImage.h>
 #include <mitkWeakPointer.h>
 
 #include <itkImageRegionIterator.h>
 #include <itkImageRegionIteratorWithIndex.h>
 
 namespace mitk {
 
 
 //##Documentation
 //## @brief Abstract superclass for histograms with double values.
 //##        Classes which are deriving from this class can be cached
 //##        in the same way.
 class MitkExt_EXPORT SimpleHistogram
 {
 public:
 
   /** @brief Returns the minimal value of the histogram. */
   virtual double GetMin() const = 0;
   /** @brief Returns the maximum value of the histogram. */
   virtual double GetMax() const = 0;
   /** @brief Creates a new histogram out the source. */
   virtual void ComputeFromBaseData( BaseData* source ) = 0;
-  /** @brief TODO: What should this method do?*/
+  /** @brief TODO: (What should this method do?)*/
   virtual float GetRelativeBin( double start, double end ) const = 0;
 };
 
 class MitkExt_EXPORT SimpleImageHistogram : public SimpleHistogram
 {
   public:
 
   SimpleImageHistogram()
   {
     valid=false;
     histogram=0;
   }
 
   ~SimpleImageHistogram()
   {
     if(histogram)
       delete histogram;
   }
 
+  /** @return Returns if the current histogram is valid, false if not. */
+  bool GetValid();
+
   typedef itk::Image<short, 3>          CTImage;
   typedef itk::ImageRegionIterator< CTImage  > CTIteratorType;
   typedef itk::ImageRegionIteratorWithIndex< CTImage  > CTIteratorIndexType;
 
   typedef itk::Image<unsigned char, 3> BinImage;
   typedef itk::ImageRegionIterator< BinImage > BinIteratorType;
   typedef itk::ImageRegionIteratorWithIndex< BinImage > BinIteratorIndexType;
 
   typedef unsigned long CountType;
 
   protected:
 
   CountType *histogram;
 
   bool valid;
 
   int first;
   int last;
   int min;
   int max;
   CountType highest;
   double invLogHighest;
 
   public:
 
   double GetMin() const
   {
     if(!valid)
       return 0;
 
     return min;
   }
 
   double GetMax() const
   {
     if(!valid)
       return 1;
 
     return max;
   }
 
+  /** @brief Creates a new histogram out the source which must be an image. Method does nothing if the image is invalid, NULL, etc.. */
   void ComputeFromBaseData( BaseData* source );
   float GetRelativeBin( double start, double end ) const;
 
 };
 
 class MitkExt_EXPORT SimpleHistogramCache
 {
   public:
 
     static const unsigned int maxCacheSize = 64;
 
     class Element
     {
       public:
         mitk::WeakPointer<BaseData> baseData;
         itk::TimeStamp m_LastUpdateTime;
 
         virtual void ComputeFromBaseData(BaseData* baseData) = 0;
         virtual SimpleHistogram* GetHistogram() = 0;
     };
 
     typedef std::list<Element*> CacheContainer;
 
     CacheContainer cache;
 
     SimpleHistogramCache()
     {
 
     }
 
     ~SimpleHistogramCache()
     {
       TrimCache(true);
     }
 
     SimpleHistogram *operator[](BaseData::Pointer sp_BaseData);
 
   protected:
 
     void TrimCache(bool full=false)
     {
       unsigned int targetSize = full?0:maxCacheSize;
 
       while(cache.size()>targetSize)
       {
         delete cache.back();
         cache.pop_back();
       }
 
     }
 };
 
 }
 
 #endif // MITKSIMPLEHISTOGRAM_H