Image Viewer GUI fails to properly map coordinates

I am trying to piece together PyQt5 based image viewer Python code from various sources and extend capability to crop regions of interest (ROI) within loaded images. The issue is that the mapped coordinates and mouse clicks consider scroll bar and menu bar when determining pixel locations. Following is the code that loads image and provide bounding box capability, but I cannot seem to draw/crop boxes accurately due to the offset.

from PyQt5.QtCore import QDir, Qt
from PyQt5.QtGui import QImage, QPainter, QPalette, QPixmap
from PyQt5.QtWidgets import (QAction, QApplication, QFileDialog, QLabel,
        QMainWindow, QMenu, QMessageBox, QScrollArea, QSizePolicy)
from PyQt5.QtPrintSupport import QPrintDialog, QPrinter


class ImageViewer(QMainWindow):
    def __init__(self):
        super(ImageViewer, self).__init__()

        self.printer = QPrinter()
        self.scaleFactor = 0.0

        self.imageLabel = QLabel()
        self.imageLabel.setBackgroundRole(QPalette.Base)
        self.imageLabel.setSizePolicy(QSizePolicy.Ignored, QSizePolicy.Ignored)
        self.imageLabel.setScaledContents(True)

        self.scrollArea = QScrollArea()
        self.scrollArea.setBackgroundRole(QPalette.Dark)
        self.scrollArea.setWidget(self.imageLabel)
        self.setCentralWidget(self.scrollArea)

        self.createActions()
        self.createMenus()

        self.setWindowTitle("Image Viewer")
        self.resize(500, 400)

    def open(self):
        fileName, _ = QFileDialog.getOpenFileName(self, "Open File",
                QDir.currentPath())
        if fileName:
            image = QImage(fileName)
            if image.isNull():
                QMessageBox.information(self, "Image Viewer",
                        "Cannot load %s." % fileName)
                return

            self.imageLabel.setPixmap(QPixmap.fromImage(image))
            self.scaleFactor = 1.0

            self.printAct.setEnabled(True)
            self.fitToWindowAct.setEnabled(True)
            self.updateActions()

            if not self.fitToWindowAct.isChecked():
                self.imageLabel.adjustSize()

    def print_(self):
        dialog = QPrintDialog(self.printer, self)
        if dialog.exec_():
            painter = QPainter(self.printer)
            rect = painter.viewport()
            size = self.imageLabel.pixmap().size()
            size.scale(rect.size(), Qt.KeepAspectRatio)
            painter.setViewport(rect.x(), rect.y(), size.width(), size.height())
            painter.setWindow(self.imageLabel.pixmap().rect())
            painter.drawPixmap(0, 0, self.imageLabel.pixmap())

    def zoomIn(self):
        self.scaleImage(1.25)

    def zoomOut(self):
        self.scaleImage(0.8)

    def normalSize(self):
        self.imageLabel.adjustSize()
        self.scaleFactor = 1.0

    def fitToWindow(self):
        fitToWindow = self.fitToWindowAct.isChecked()
        self.scrollArea.setWidgetResizable(fitToWindow)
        if not fitToWindow:
            self.normalSize()

        self.updateActions()

    def about(self):
        QMessageBox.about(self, "About Image Viewer",
                "<p>The <b>Image Viewer</b> example shows how to combine "
                "QLabel and QScrollArea to display an image. QLabel is "
                "typically used for displaying text, but it can also display "
                "an image. QScrollArea provides a scrolling view around "
                "another widget. If the child widget exceeds the size of the "
                "frame, QScrollArea automatically provides scroll bars.</p>"
                "<p>The example demonstrates how QLabel's ability to scale "
                "its contents (QLabel.scaledContents), and QScrollArea's "
                "ability to automatically resize its contents "
                "(QScrollArea.widgetResizable), can be used to implement "
                "zooming and scaling features.</p>"
                "<p>In addition the example shows how to use QPainter to "
                "print an image.</p>")

    def createActions(self):
        self.openAct = QAction("&Open...", self, shortcut="Ctrl+O",
                triggered=self.open)

        self.printAct = QAction("&Print...", self, shortcut="Ctrl+P",
                enabled=False, triggered=self.print_)

        self.exitAct = QAction("E&xit", self, shortcut="Ctrl+Q",
                triggered=self.close)

        self.zoomInAct = QAction("Zoom &In (25%)", self, shortcut="Ctrl++",
                enabled=False, triggered=self.zoomIn)

        self.zoomOutAct = QAction("Zoom &Out (25%)", self, shortcut="Ctrl+-",
                enabled=False, triggered=self.zoomOut)

        self.normalSizeAct = QAction("&Normal Size", self, shortcut="Ctrl+S",
                enabled=False, triggered=self.normalSize)

        self.fitToWindowAct = QAction("&Fit to Window", self, enabled=False,
                checkable=True, shortcut="Ctrl+F", triggered=self.fitToWindow)

        self.aboutAct = QAction("&About", self, triggered=self.about)

        self.aboutQtAct = QAction("About &Qt", self,
                triggered=QApplication.instance().aboutQt)

    def createMenus(self):
        self.fileMenu = QMenu("&File", self)
        self.fileMenu.addAction(self.openAct)
        self.fileMenu.addAction(self.printAct)
        self.fileMenu.addSeparator()
        self.fileMenu.addAction(self.exitAct)

        self.viewMenu = QMenu("&View", self)
        self.viewMenu.addAction(self.zoomInAct)
        self.viewMenu.addAction(self.zoomOutAct)
        self.viewMenu.addAction(self.normalSizeAct)
        self.viewMenu.addSeparator()
        self.viewMenu.addAction(self.fitToWindowAct)

        self.helpMenu = QMenu("&Help", self)
        self.helpMenu.addAction(self.aboutAct)
        self.helpMenu.addAction(self.aboutQtAct)

        self.menuBar().addMenu(self.fileMenu)
        self.menuBar().addMenu(self.viewMenu)
        self.menuBar().addMenu(self.helpMenu)

    def updateActions(self):
        self.zoomInAct.setEnabled(not self.fitToWindowAct.isChecked())
        self.zoomOutAct.setEnabled(not self.fitToWindowAct.isChecked())
        self.normalSizeAct.setEnabled(not self.fitToWindowAct.isChecked())

    def scaleImage(self, factor):
        self.scaleFactor *= factor
        self.imageLabel.resize(self.scaleFactor * self.imageLabel.pixmap().size())

        self.adjustScrollBar(self.scrollArea.horizontalScrollBar(), factor)
        self.adjustScrollBar(self.scrollArea.verticalScrollBar(), factor)

        self.zoomInAct.setEnabled(self.scaleFactor < 3.0)
        self.zoomOutAct.setEnabled(self.scaleFactor > 0.333)

    def adjustScrollBar(self, scrollBar, factor):
        scrollBar.setValue(int(factor * scrollBar.value()
                                + ((factor - 1) * scrollBar.pageStep()/2)))


    def mousePressEvent (self, eventQMouseEvent):
        self.originQPoint = self.scrollArea.mapFrom(self, eventQMouseEvent.pos())
        #self.originQPoint = eventQMouseEvent.pos()
        self.currentQRubberBand = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle, self)
        self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, QtCore.QSize()))
        self.currentQRubberBand.show()

    def mouseMoveEvent (self, eventQMouseEvent):
        self.x = int(eventQMouseEvent.x())
        self.y = int(eventQMouseEvent.y())
        text1 = str(self.x)
        text2 = str(self.y)
        #print(self.x,self.y)
        QtWidgets.QToolTip.showText(eventQMouseEvent.pos() , "X: "+text1+" "+"Y: "+text2,self)
        if self.currentQRubberBand.isVisible():
            self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, eventQMouseEvent.pos()).normalized() & self.imageLabel.pixmap().rect())

    def mouseReleaseEvent (self, eventQMouseEvent):
        self.currentQRubberBand.hide()
        currentQRect = self.currentQRubberBand.geometry()
        self.currentQRubberBand.deleteLater()
        cropQPixmap = self.imageLabel.pixmap().copy(currentQRect)
        cropQPixmap.save('output.png')

if __name__ == '__main__':
    import sys
    from PyQt5 import QtGui, QtCore, QtWidgets

    app = QApplication(sys.argv)
    imageViewer = ImageViewer()
    imageViewer.show()
    sys.exit(app.exec_())

It is better in these cases that the QRubberBand is the son of the QLabel so there will be no need to make many transformations.

On the other hand, the coordinates of the event are related to the window, so we have to convert it to the coordinates of the QLabel. For this a simple methodology is to convert the local coordinate with respect to the window to global coordinates and then the global coordinates to local coordinates with respect to the QLabel.

And finally when you scale the image you affect the coordinates since the currentQRect is relative to the scaled QLabel but the internal QPixmap is not scaled.

def mousePressEvent (self, event):
    self.originQPoint = self.imageLabel.mapFromGlobal(self.mapToGlobal(event.pos())) 
    self.currentQRubberBand = QtWidgets.QRubberBand(QtWidgets.QRubberBand.Rectangle, self.imageLabel)
    self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, QtCore.QSize()))
    self.currentQRubberBand.show()

def mouseMoveEvent (self, event):
    p = self.imageLabel.mapFromGlobal(self.mapToGlobal(event.pos()))
    QtWidgets.QToolTip.showText(event.pos() , "X: {} Y: {}".format(p.x(), p.y()), self)
    if self.currentQRubberBand.isVisible() and self.imageLabel.pixmap() is not None:
        self.currentQRubberBand.setGeometry(QtCore.QRect(self.originQPoint, p).normalized() & self.imageLabel.rect())

def mouseReleaseEvent (self, event):
    self.currentQRubberBand.hide()
    currentQRect = self.currentQRubberBand.geometry()
    self.currentQRubberBand.deleteLater()
    if self.imageLabel.pixmap() is not None:
        tr = QtGui.QTransform()
        if self.fitToWindowAct.isChecked():
            tr.scale(self.imageLabel.pixmap().width()/self.scrollArea.width(), 
                self.imageLabel.pixmap().height()/self.scrollArea.height())
        else:
            tr.scale(1/self.scaleFactor, 1/self.scaleFactor)
        r = tr.mapRect(currentQRect)
        cropQPixmap = self.imageLabel.pixmap().copy(r)
        cropQPixmap.save('output.png')