title: QPixmap not safe outside GUI thread
body: <p>My program has the main GUI thread to handle the user interface.</p>
  
  <p>Another thread is started to handle the hard work (loops, calculations, etc) without freezing the main GUI.</p>
  
  <p>From my "calculations thread" I am using another module <code>draw_plots</code> which only draws and saves many kinds of plots.</p>
  
  <pre><code>import draw_plots as plots
      class calculatorThread(QtCore.QThread):
          signal1 = QtCore.pyqtSignal(int, int)
          signal2 = QtCore.pyqtSignal(int,int) 
          signal3 = QtCore.pyqtSignal(int) 
  
          def __init__(self,input_file_txt, parameter_file_txt):
              QtCore.QThread.__init__(self)
              #and etc etc
  </code></pre>
  
  <p>At some point of this thread I am calling:</p>
  
  <pre><code>plots.stacked_barplot(*arguments)
  </code></pre>
  
  <p>Everything works fine, however, I get a message on the screen many many times:</p>
  
  <pre><code>QPixmap: It is not safe to use pixmaps outside the GUI thread
  </code></pre>
  
  <p>Would like to know what am I doing wrong and how to avoid this message.</p>