VTK GetScalarPointer() and GetScalarComponentAsFloat() not work

#include <vtkVersion.h>
#include <vtkSmartPointer.h>
#include <vtkImageData.h>
#include <vtkPointData.h>
#include "vtkBMPReader.h"

int main(int, char *[])
{
    char * filename = "img.bmp";
    if( !filename  || strlen(filename) == 0 )
    {
        return -1;
    }

    vtkBMPReader * reader = vtkBMPReader::New();
    reader->SetFileName(filename);
    reader->Update();

    vtkSmartPointer<vtkImageData> image_data = reader->GetOutput();

    int* dims = image_data->GetDimensions();
    std::cout << "Dims: " << " x: " << dims[0] << " y: " << dims[1] << " z: " << dims[2] << std::endl;
    std::cout << "Number of points: " << image_data->GetNumberOfPoints() << std::endl;
    std::cout << "Number of cells: " << image_data->GetNumberOfCells() << std::endl;
    std::cout << "Number of scalar components: " << image_data->GetNumberOfScalarComponents() << std::endl;

    vtkDataArray *arr = image_data->GetPointData()->GetArray(0);

    // Retrieve the entries from the image data and print them to the screen
    for (int z = 0; z < dims[2]; z++)
    {
        for (int y = 0; y < dims[1]; y++)
        {
            for (int x = 0; x < dims[0]; x++)
            {
                /* Change this
                double* pixel = static_cast<double*>(imageData->GetScalarPointer(x,y,z));
                // do something with v
                std::cout << pixel[0] << " ";
                */
                double d[3];
                arr->GetTuple(y * dims[0] + x, d);
                std::cout << d[0] << " ";
            }
            std::cout << std::endl;
        }
        std::cout << std::endl;
    }

    return EXIT_SUCCESS;
}