opencv - How can I combine these two codes? (python image viewer + image ROI crop by mouse drag)

Question

I'm beginner in Python and PyQt. I try to create image viewer based on acbetter's code and want to add image crop function. Using these two codes, ultimately I want to create a code in which I can open a certain image and crop specific part of the image and show it in another window. Would you like to help how to combine these two codes?

1. acbetter's image viewer code https://gist.github.com/acbetter/32c575803ec361c3e82064e60db4e3e0

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


class QImageViewer(QMainWindow):
    def __init__(self):
        super().__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.scrollArea.setVisible(False)

        self.setCentralWidget(self.scrollArea)

        self.createActions()
        self.createMenus()

        self.setWindowTitle("Image Viewer")
        self.resize(800, 600)

    def open(self):
        options = QFileDialog.Options()
        # fileName = QFileDialog.getOpenFileName(self, "Open File", QDir.currentPath())
        fileName, _ = QFileDialog.getOpenFileName(self, 'QFileDialog.getOpenFileName()', '',
                                                  'Images (*.png *.jpeg *.jpg *.bmp *.gif)', options=options)
        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.scrollArea.setVisible(True)
            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=qApp.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)))


if __name__ == '__main__':
    import sys
    from PyQt5.QtWidgets import QApplication

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

2. image crop code using opencv

import cv2 
mouse_is_pressing = False
start_x, start_y = -1, -1

def mouse_callback(event, x, y, flags, param):
    global start_x, start_y, mouse_is_pressing 

    img_result = src.copy()

    if event == cv2.EVENT_LBUTTONDOWN:

        mouse_is_pressing = True
        start_x, start_y = x,y

        cv2.circle(img_result, (x,y), 10, (0,255,0),-1)
        cv2.imshow("img_color", img_result)

    elif event == cv2.EVENT_MOUSEMOVE:
        if mouse_is_pressing: 
            cv2.rectangle(img_result, (start_x, start_y), (x,y), (0,255,0), 3)
            cv2.imshow("img_color", img_result)

    elif event == cv2.EVENT_LBUTTONUP:
        mouse_is_pressing = False 

        img_part = img_result[start_y:y, start_x:x]
        cv2.imshow("img_color", img_result)
        cv2.imshow("img_part", img_part)

src = cv2.imread("D:/python data/image/image.jpg")
cv2.imshow("img_color", src)
cv2.setMouseCallback("img_color", mouse_callback)
cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

Implementing the crop in a viewer based on a QScrollArea with a QLabel is unnecessarily complicated since the transformation is complicated to track, instead implement the same logic with QGraphicsView, QGraphicsScene and QGraphicsPixmapItem. So much of the logic is already implemented as I show below:

from PyQt5 import QtCore, QtGui, QtWidgets, QtPrintSupport


class Viewer(QtWidgets.QGraphicsView):
    def __init__(self, parent=None):
        super().__init__(QtWidgets.QGraphicsScene(), parent)
        self.pixmap_item = self.scene().addPixmap(QtGui.QPixmap())
        self.setAlignment(QtCore.Qt.AlignTop | QtCore.Qt.AlignLeft)
        self.setBackgroundRole(QtGui.QPalette.Dark)
        self.setDragMode(QtWidgets.QGraphicsView.RubberBandDrag)
        self.rubberBandChanged.connect(self.onRubberBandChanged)
        self.last_rect = QtCore.QPointF()

    def setPixmap(self, pixmap):
        self.pixmap_item.setPixmap(pixmap)

    def zoomIn(self):
        self.scale(1.25, 1.25)

    def zoomOut(self):
        self.scale(0.8, 0.8)

    def resetZoom(self):
        self.resetTransform()

    def fitToWindow(self):
        self.fitInView(self.pixmap_item)

    @QtCore.pyqtSlot(QtCore.QRect, QtCore.QPointF, QtCore.QPointF)
    def onRubberBandChanged(self, rubberBandRect, fromScenePoint, toScenePoint):
        if rubberBandRect.isNull():
            pixmap = self.pixmap_item.pixmap()
            rect = self.pixmap_item.mapFromScene(self.last_rect).boundingRect().toRect()
            if not rect.intersected(pixmap.rect()).isNull():
                crop_pixmap = pixmap.copy(rect)
                label = QtWidgets.QLabel(pixmap=crop_pixmap)
                dialog = QtWidgets.QDialog(self)
                lay = QtWidgets.QVBoxLayout(dialog)
                lay.addWidget(label)
                dialog.exec_()
            self.last_rect = QtCore.QRectF()
        else:
            self.last_rect = QtCore.QRectF(fromScenePoint, toScenePoint)


class QImageViewer(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super().__init__()

        self.view = Viewer()
        self.setCentralWidget(self.view)

        self.printer = QtPrintSupport.QPrinter()

        self.createActions()
        self.createMenus()

        self.setWindowTitle("Image Viewer")
        self.resize(800, 600)

    def open(self):
        fileName, _ = QtWidgets.QFileDialog.getOpenFileName(
            self,
            "QFileDialog.getOpenFileName()",
            "",
            "Images (*.png *.jpeg *.jpg *.bmp *.gif)",
        )
        if fileName:
            pixmap = QtGui.QPixmap(fileName)
            if pixmap.isNull():
                QtWidgets.QMessageBox.information(
                    self, "Image Viewer", "Cannot load %s." % fileName
                )
                return

            self.view.setPixmap(pixmap)

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

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

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

    def fitToWindow(self):
        if self.fitToWindowAct.isChecked():
            self.view.fitToWindow()
        else:
            self.view.resetZoom()
        self.updateActions()

    def about(self):
        QtWidgets.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 = QtWidgets.QAction(
            "&Open...", self, shortcut="Ctrl+O", triggered=self.open
        )
        self.printAct = QtWidgets.QAction(
            "&Print...", self, shortcut="Ctrl+P", enabled=False, triggered=self.print_
        )
        self.exitAct = QtWidgets.QAction(
            "E&xit", self, shortcut="Ctrl+Q", triggered=self.close
        )
        self.zoomInAct = QtWidgets.QAction(
            "Zoom &In (25%)",
            self,
            shortcut="Ctrl++",
            enabled=False,
            triggered=self.view.zoomIn,
        )
        self.zoomOutAct = QtWidgets.QAction(
            "Zoom &Out (25%)",
            self,
            shortcut="Ctrl+-",
            enabled=False,
            triggered=self.view.zoomOut,
        )
        self.normalSizeAct = QtWidgets.QAction(
            "&Normal Size",
            self,
            shortcut="Ctrl+S",
            enabled=False,
            triggered=self.view.resetZoom,
        )
        self.fitToWindowAct = QtWidgets.QAction(
            "&Fit to Window",
            self,
            enabled=False,
            checkable=True,
            shortcut="Ctrl+F",
            triggered=self.fitToWindow,
        )
        self.aboutAct = QtWidgets.QAction("&About", self, triggered=self.about)
        self.aboutQtAct = QtWidgets.QAction(
            "About &Qt", self, triggered=QtWidgets.qApp.aboutQt
        )

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

        self.viewMenu = QtWidgets.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 = QtWidgets.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())


if __name__ == "__main__":
    import sys
    from PyQt5.QtWidgets import QApplication

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