[vtkusers] function of SetDataMask in vtkImageReader

[付文宇]

Hi everyone:
   I use vtkImageReader to read a stack of image data.In vtk user guide,there are
many examples of using vtkImgeReader,such as 
------------------------------------------------------------------------
v16 = vtkImageReader::New();
v16->SetDataByteOrderToLittleEndian();
v16->SetDataExtent(0,m_xNum-1,0,m_yNum-1,m_startClipNum,m_endClipNum);
v16->SetDataOrigin(m_xOfOrigin,m_yOfOrigin,m_zOfOrigin);
v16->SetFilePrefix(m_filePathName);
v16->SetDataMask(0x7fff);        
v16->SetDataSpacing(m_xOfSpace,m_yOfSpace,m_zOfSpace);
---------------------------------------------------------------------------
But I donot know the role of "v16->SetDataMask(0x7fff);". I delete the code of
this line ,and I can render volume data too. From the name of "SetDataMask", I
guess it may be used to filter soome data. Could someone give me an explanation in
detail?
Thanks in advance.

Fu wenyu
2007.05.14