图像查看器 GUI 无法正确映射鼠标按下事件的坐标

Question

我正在尝试将来自各种来源的基于 PyQt5 的图像查看器 Python 代码拼凑在一起，并扩展功能以在加载的图像中裁剪感兴趣区域 (ROI)。问题是映射坐标和鼠标点击在确定像素位置时会考虑滚动条和菜单栏。以下是加载图像并提供边界框功能的代码，但由于偏移，我似乎无法准确地绘制/裁剪框。

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_())

Answer 1

在这些情况下，QRubberBand 最好是 QLabel 的儿子，这样就不需要进行很多转换。

另一方面，事件的坐标与窗口有关，所以我们必须将其转换为 QLabel 的坐标。为此，一种简单的方法是将相对于窗口的局部坐标转换为全局坐标，然后将全局坐标转换为相对于 QLabel 的局部坐标。

最后，当您缩放图像时，您会影响坐标，因为 currentQRect 是相对于缩放的 QLabel，但内部 QPixmap 没有缩放。

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')