[vtkusers] why the color of actor is white by seting the vtkLookupTable

[朱文武]

hi all,

      I sent the message last night!  However, no one responded ! So, i send
it again. Please forgive me, if it disrupts you!

I use vtkDiscreteMarchingCubes to reconstruct anatomy structure, and use the
vtkLookupTable to map the color. Now, i design the color map as follows:
gray value (111) to red,
gray value(121) to blue.
Other gray value I don't care.

Also, the parameter I set in SetValue() of  vtkDiscreteMarchingCubes is:
SetValue(0, 111);
SetValue(1, 121);

Then i set the lookup table as follows:
vtkSmartPointer<vtkLookupTable> colorLookupTable=
vtkSmartPointer<vtkLookupTable>::New();
colorLookupTable->SetTableRange(0, 122); //
colorLookupTable->SetNumberOfTableValues(123);
colorLookupTable->Build();

for (int i =0; i < 111; i++)
{
    colorLookupTable->SetTableValue(i , i/255.0, i/255.0,i/255.0); // i
don't care this loop
}
colorLookupTable->SetTableValue(111, 1,0,0,1); // this is essential for me
for (int j = 112; j <120; j++)
{
    colorLookupTable->SetTableValue(j , j/255.0, j/255.0, j/255.0); // i
don't care this loop

}
colorLookupTable->SetTableValue(121, 0,0,1,1);
colorLookupTable->SetTableValue(122, 0,0,1,1);

vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
...
mapper->ScalarVisibilityOn() ;//#show colour
mapper->SetScalarRange(colorLookupTable->GetTableRange());
mapper->SetScalarModeToUseCellData() ;
mapper->SetLookupTable(colorLookupTable);

The result of construction is that two structures whose gray value is 111
and 121 were reconstructed.
However, the color of these actors is the same- white.
Ccould anyone tell me why and give some suggestions?

Thanks
Wenwu
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