[vtkusers] How to display images with negative pixelar value?

[Rodrigues, Jason (MED)]

CAn anybody guide me as to how to display the negative pixels values Images
on to the ImageViewer or rendered using the common mappers? 
   
      vtkImageMapper imgMapper = new vtkImageMapper();
             imgMapper.SetInput(imagedata1);
             imgMapper.SetColorWindow(4000);
             imgMapper.SetColorLevel(2000);

         vtkActor2D actor = new vtkActor2D();
            actor.SetMapper(imgMapper);

         vtkRenderer ren=panel1.getRenderer();
            ren.AddActor2D(actor);

  Here imagedata1 contains pixel values in both +ve and -ve domain. the
image in the negative domain seems to have been blackenend upon display. 

 Can anyone tell me as to why is the mappers/ imageviewer colorlevel is
usually kept half the colorwindow ? 
Regards,
JASON


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