如何从 QGraphicsScene 仅获取图像像素

Question

这是我在 pyqt python 3.7 中的 QGraphicsView 中显示图像的简单代码。当鼠标在 QGraphicsView 或 QGraphicsScene 的场景或窗口上按下时，我想要一个图像像素。

鼠标按下功能

鼠标按下事件处理程序

def mousePressEvent(self):
    p = QtGui.QCursor.pos()
    print("pressed here: ", p)

鼠标按下事件调用者

self.scene1.mousePressEvent = mousePressEvent

主代码

 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_())

Answer 1

您不应修改 Qt Designer 生成的类⁽¹⁾，而应创建另一个从小部件继承的类并将初始类用作接口。

不要使用 self.scene1.mousePressEvent = mousePressEvent 覆盖 mousePressEvent 方法，因为您正在删除默认实现，而是可以创建一个继承自 QGraphicsScene 的类或使用事件过滤器，在这种情况下我将使用第二种方法。

要获得鼠标相对于图像的位置 (QGraphicsPixmapItem)，您必须使用 Qt 图形框架的不同元素之间的转换。

import os

import cv2
from PyQt5 import QtCore, QtGui, QtWidgets


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)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))


class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, parent=None):
        super().__init__(parent)
        self.setupUi(self)

        self.scene = QtWidgets.QGraphicsScene(self)
        self.graphicsView.setScene(self.scene)
        self.scene.installEventFilter(self)

        current_dir = os.path.dirname(os.path.realpath(__file__))
        filename = os.path.join(current_dir, "lena.jpg")

        image = cv2.imread(filename)
        image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
        height, width = image.shape
        image_disp = QtGui.QImage(
            image.data, width, height, QtGui.QImage.Format_Grayscale8
        )
        pixMap = QtGui.QPixmap.fromImage(image_disp)
        self.pixmap_item = self.scene.addPixmap(pixMap)

    def eventFilter(self, obj, event):
        if obj is self.scene and event.type() == QtCore.QEvent.GraphicsSceneMousePress:
            spf = event.scenePos()
            lpf = self.pixmap_item.mapFromScene(spf)
            brf = self.pixmap_item.boundingRect()
            if brf.contains(lpf):
                lp = lpf.toPoint()
                print(lp)
        return super().eventFilter(obj, event)


if __name__ == "__main__":
    import sys

    app = QtWidgets.QApplication(sys.argv)
    w = MainWindow()
    w.show()
    sys.exit(app.exec_())

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^{(1)Using the Generated Code}