ADD_ELXCOMPONENT( GradientDifferenceMetric OFF
 elxGradientDifferenceMetric.h
 elxGradientDifferenceMetric.hxx
 elxGradientDifferenceMetric.cxx
 itkGradientDifferenceImageToImageMetric2.h
 itkGradientDifferenceImageToImageMetric2.hxx )