[vtk-developers] Interesting problem building a vtkLookupTable from vtkColorSeries.

[Andrew Maclean]

I wanted to generate a lookup table from vtkCOlor series using
BuildLookupTable().
However the only way I can do it is to create a second lookup table and
copy from the first to the second one.
I thought I could do this:
    colorSeries = vtk.vtkColorSeries()
    colorSeriesEnum = colorSeries.BREWER_DIVERGING_BROWN_BLUE_GREEN_10
    colorSeries.SetColorScheme(colorSeriesEnum)
    lut = vtk.vtkLookupTable()
    colorSeries.BuildLookupTable(lut)

But I have to do this:
    colorSeries = vtk.vtkColorSeries()
    colorSeriesEnum = colorSeries.BREWER_DIVERGING_BROWN_BLUE_GREEN_10
    colorSeries.SetColorScheme(colorSeriesEnum)
    lut1 = vtk.vtkLookupTable()
    colorSeries.BuildLookupTable(lut1)
    lut = vtk.vtkLookupTable()
    lut.SetNumberOfTableValues(lut1.GetNumberOfTableValues())
    for i in range(0,lut1.GetNumberOfTableValues()):
        lut.SetTableValue(i,lut1.GetTableValue(i))

In looking at the code in vtkColorSeries.cxx, namely:
//-----------------------------------------------------------------------------
void vtkColorSeries::BuildLookupTable(vtkLookupTable* lkup)
{
  if (lkup)
    {
    lkup->SetNumberOfTableValues(this->GetNumberOfColors());
    lkup->IndexedLookupOn();
    for (int i = 0; i < this->GetNumberOfColors(); ++i)
      {
      vtkColor3ub colr = this->GetColor(i);
      lkup->SetTableValue(
        i, colr.GetRed()/255., colr.GetGreen()/255., colr.GetBlue()/255.,
1.);
      }
    }
}
It seems lkup is built correctly.

I can't see any reason for building and then copying to a new table.

I would appreciate it if anyone could point out what I am missing.

I have also attached a Python script that illustrates this.

Regards
   Andrew
-- 
___________________________________________
Andrew J. P. Maclean

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