title: Pyqt get pixel position and value when mouse click on the image
body: <p>Overwriting mouse event on pixMapItem didn't work for me ; the mouse click event is not detected by the pixMapItem. Here is my code :</p>
  
  <pre><code>import sys
  from PyQt4.QtCore import *
  from PyQt4.QtGui import *
  
  class DrawImage( QMainWindow ):
      def __init__(self, path):
  
          QMainWindow.__init__(self)
          self.setWindowTitle('Select Window')
          self.local_image = QImage(path)
  
          self.local_grview = QGraphicsView()
          self.setCentralWidget( self.local_grview )
  
          self.local_scene = QGraphicsScene()
  
          self.image_format = self.local_image.format()
          self.pixMapItem = self.local_scene.addPixmap( QPixmap(self.local_image) )
          self.local_grview.setScene( self.local_scene )
  
  
  
  
          self.pixMapItem.mousePressEvent = self.pixelSelect
  
          self.show()
          sys.exit(app.exec_())
  
      def pixelSelect( self, event ):
          print 'hello'
          position = QPoint( event.pos().x(),  event.pos().y())
          color = QColor.fromRgb(self.local_image.pixel( position ) )
          if color.isValid():
              rgbColor = '('+str(color.red())+','+str(color.green())+','+str(color.blue())+','+str(color.alpha())+')'
              self.setWindowTitle( 'Pixel position = (' + str( event.pos().x() ) + ' , ' + str( event.pos().y() )+ ') - Value (R,G,B,A)= ' + rgbColor)
          else:
              self.setWindowTitle( 'Pixel position = (' + str( event.pos().x() ) + ' , ' + str( event.pos().y() )+ ') - color not valid')
  </code></pre>