[vtkusers] Difference between vtkVolume16Reader and vtkImageReader?

[xujf]

hello, all:

     In oder to read vtkImageData, I employ two different classes- vtkimagereader, vtkvolume16reader. however,the result read by vtkvolume16reader is distorted, while the one read by vtkimagereader is very good.
     I wonder what is the difference between the class vtkvolume16reader and vtkimagdata and which kinds of datasets they are suitable to read respectively.

xujf