using vtkActor2D along with vtkImageCanvasSource2D results in wrong color

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Hi Paulo,
Thanks for reply. In several examples(eg. this and this) they all used unsigned char as scalar types for vtkImageCanvasSource2D class. If I change my code to using double, ie.

  vtkNew<vtkImageCanvasSource2D> source;
    source->SetScalarTypeToDouble();
    source->SetExtent(extent);
    source->SetNumberOfScalarComponents(4); // Ensure 4 components for RGBA
    source->SetDrawColor(0, 0, 0, 0); // Transparent background
    source->FillBox(extent[0], extent[1], extent[2], extent[3]);
    source->SetDrawColor(1.0, 1.0, 0, 1.0); // Yellow color with full opacity
    source->DrawCircle(200, 100, 30);
    source->Update();

nothing will be shown.

Regards