itk::ImageRegionConstIterator<Input1ImageType> it1(input1, input1Region);
itk::ImageRegionConstIterator<Input2ImageType> it2(input2, input2Region);
itk::ImageRegionIterator<OutputImageType> ot (output, outputRegion);
itk::ImageRegionConstIterator<Input1ImageType> it1(input1, input1Region);
itk::ImageRegionConstIterator<Input2ImageType> it2(input2, input2Region);
itk::ImageRegionIterator<OutputImageType> ot (output, outputRegion);