printing with QwtPlot::print

[user]

I created a plot and I would like to print it.
From the Qwt examples, I used the bode example to create a print function:

void plotsMainWindow::print( ResultsPlot * plot )
{
  QPrinter printer;
  printer.setOrientation( QPrinter::Landscape );
  QPrintDialog dialog( &printer );
  if ( dialog.exec() )
  {
    QwtPlotPrintFilter filter;
    if ( printer.colorMode() == QPrinter::GrayScale )
    {
      filter.setOptions ( QwtPlotPrintFilter::PrintAll & ~QwtPlotPrintFilter::PrintCanvasBackground );
    }
    plot->print( printer, filter );
  }
}

void plotsMainWindow::print( ResultsPlot * plot )
{
  QPrinter printer;
  printer.setOrientation( QPrinter::Landscape );
  QPrintDialog dialog( &printer );
  if ( dialog.exec() )
  {
    QwtPlotPrintFilter filter;
    if ( printer.colorMode() == QPrinter::GrayScale )
    {
      filter.setOptions ( QwtPlotPrintFilter::PrintAll & ~QwtPlotPrintFilter::PrintCanvasBackground );
    }
    plot->print( printer, filter );
  }
}

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When I try to print to a pdf document, the plot is printed but I have a light gray background.
I would like the plot on a white background, or no background at all.
When defining the canvas for the plot I used:

canvas_->setBackgroundRole( QPalette::Window );
canvas_->setAutoFillBackground( true );

canvas_->setBackgroundRole( QPalette::Window );
canvas_->setAutoFillBackground( true );

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the displayed plot on the screen shows a window background but it's different in the printing.

Also the documentation says that QwtPlotPrintFilter will be removed in future versions.
Should I use a different way to print the plot?