Displayin an Image in a QGraphicsScene

Question

I have a short script that modifies an image with PIL several times. I would like to be able to display the intermediate steps as it finishes with them, so I added a QGraph

Answer 1

It is hard to determine your problem without loop code and working example. But i have similar test application, hope it will help.

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
import Image
import ImageQt
import ImageEnhance
import time

class TestWidget(QWidget):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.scene = QGraphicsScene()
        self.view = QGraphicsView(self.scene)
        self.button = QPushButton("Do test")

        layout = QVBoxLayout()
        layout.addWidget(self.button)
        layout.addWidget(self.view)
        self.setLayout(layout)

        self.button.clicked.connect(self.do_test)

    def do_test(self):
        img = Image.open('image.png')
        enhancer = ImageEnhance.Brightness(img)
        for i in range(1, 8):
            img = enhancer.enhance(i)
            self.display_image(img)
            QCoreApplication.processEvents()  # let Qt do his work
            time.sleep(0.5)

    def display_image(self, img):
        self.scene.clear()
        w, h = img.size
        self.imgQ = ImageQt.ImageQt(img)  # we need to hold reference to imgQ, or it will crash
        pixMap = QPixmap.fromImage(self.imgQ)
        self.scene.addPixmap(pixMap)
        self.view.fitInView(QRectF(0, 0, w, h), Qt.KeepAspectRatio)
        self.scene.update()

if __name__ == "__main__":
    app = QApplication(sys.argv)
    widget = TestWidget()
    widget.resize(640, 480)
    widget.show()

    sys.exit(app.exec_())

The main points:

• If you are doing some processing or sleep in loop, you need to call QCoreApplication.processEvents() to allow Qt to do updates.

• I'm saving reference to ImageQt.ImageQt (self.imgQ) or it will crash.

• As I understood, you are creating QGraphicsScene in each iteration, better solution to create it once and then call scene.clear().

• Scaling pixmap just to display it sized and centered is expensive, QGraphicsView.fitInView() maked for this purpose.