title: how to get only image pixel from QGraphicsScene
body: <p>here is my simple code to display the image in QGraphicsView in pyqt python 3.7. I want an image pixel when the mouse is pressed on a scene or window of QGraphicsView or QGraphicsScene.</p>
  
  <p>Mouse Press Function </p>
  
  <p>Mouse Press Event Handler</p>
  
  <pre><code>def mousePressEvent(self):
      p = QtGui.QCursor.pos()
      print("pressed here: ", p)
  </code></pre>
  
  <p>Mouse Press Event caller</p>
  
  <pre><code>self.scene1.mousePressEvent = mousePressEvent
  </code></pre>
  
  <p>Main Code</p>
  
  <pre><code> import cv2
   from PyQt5 import QtCore, QtGui, QtWidgets
   from PyQt5.QtGui import *
   from PyQt5.QtWidgets import QGraphicsScene, QAction
  
  
  class Ui_MainWindow(object):
      def setupUi(self, MainWindow):
          MainWindow.setObjectName("MainWindow")
          MainWindow.resize(800, 600)
          self.centralwidget = QtWidgets.QWidget(MainWindow)
          self.centralwidget.setObjectName("centralwidget")
          self.graphicsView = QtWidgets.QGraphicsView(self.centralwidget)
          self.graphicsView.setGeometry(QtCore.QRect(20, 10, 761, 561))
          self.graphicsView.setObjectName("graphicsView")
          MainWindow.setCentralWidget(self.centralwidget)
          self.statusbar = QtWidgets.QStatusBar(MainWindow)
          self.statusbar.setObjectName("statusbar")
          MainWindow.setStatusBar(self.statusbar)
  
          self.retranslateUi(MainWindow)
          QtCore.QMetaObject.connectSlotsByName(MainWindow)
  
          #  ---- Mouse Press Event Handler ---- #
          def mousePressEvent(self):
              p = QtGui.QCursor.pos()  # Here I want image pixel coordinate (x,y) how we can..?
              print("pressed here: ", p)
  
          #  ---- Mouse Press Event caller ---- #
          self.scene1.mousePressEvent = mousePressEvent
  
      def retranslateUi(self, MainWindow):
          _translate = QtCore.QCoreApplication.translate
          MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
  
          # -------------------------------------------------
          image = cv2.imread('lena.jpg')  # Read image
          image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
  
          height, width = image.shape  # read image size
          self.image_disp = QImage(image.data, width, height, QImage.Format_Grayscale8)
          # -------------------------------------------------
          self.scene1 = QGraphicsScene()
          pixMap = QPixmap.fromImage(self.image_disp)
          self.scene1.addPixmap(pixMap)
          self.graphicsView.setScene(self.scene1)
  
  if __name__ == "__main__":
      import sys
      app = QtWidgets.QApplication(sys.argv)
      MainWindow = QtWidgets.QMainWindow()
      ui = Ui_MainWindow()
      ui.setupUi(MainWindow)
      MainWindow.show()
      sys.exit(app.exec_())
  </code></pre>