How to combine OpenCV with PyQt to create a simple GUI?

Question

I need to perform lot of operations on an image. So I used OpenCV. OpenCV is very efficient in image processing, however it is not too good to present a suitable GUI. So I decided to use PyQt to draw a custom GUI and OpenCV to process my image.

I created a very simple program you directly picked from the documentation. I simply read a jpg picture and save it in a png format by pressing the key s.

My aim is to replace the key s with a button to press to perform the same action using PyQt. Also, I want the window displayed by PyQt to have the same behavior as OpenCV: mainly speaking, the function imshow() displays a window that fits to the image size.

Here is my OpenCV simple code:

import numpy 
import cv2

class LoadImage:
    def loadImage(self):
        img = cv2.imread('photo.jpg')
        cv2.imshow('Image on a window',img)
        k = cv2.waitKey(0)
        if k == 27:
            cv2.destroyAllWindows()
        elif k == ord('s'):
            cv2.imwrite('photopng.png',img)
            cv2.destroyAllWindows()

if __name__=="__main__":
    LI=LoadImage()
    LI.loadImage()

Output:

Here is a simple PyQt code to draw a simple window:

import sys
from PyQt4 import QtGui

class DrawWindow:
    def drawWindow(self):
        app=QtGui.QApplication(sys.argv)
        w=QtGui.QWidget()
        #w.resize(250,250)
        w.move(300,300)
        w.setWindowTitle("Simple Window")
        w.show()

        sys.exit(app.exec_())

if __name__=="__main__":
    DW=DrawWindow()
    DW.drawWindow()

How can I mix the 2 codes to reach my goal?

Answer 1

Modified some code basing on your post, I didn't use the Opencv to render the image, instead using QPixmap to render it. then use KeyPressEvent to capture the user input .

# -*- coding: utf-8 -*-


import numpy
import cv2
from PyQt4.QtGui import *
from PyQt4.QtCore import *


class MyDialog(QDialog):
    def __init__(self, parent=None):
        super(MyDialog, self).__init__(parent)

        self.cvImage = cv2.imread(r'cat.jpg')
        height, width, byteValue = self.cvImage.shape
        byteValue = byteValue * width

        cv2.cvtColor(self.cvImage, cv2.COLOR_BGR2RGB, self.cvImage)

        self.mQImage = QImage(self.cvImage, width, height, byteValue, QImage.Format_RGB888)

    def paintEvent(self, QPaintEvent):
        painter = QPainter()
        painter.begin(self)
        painter.drawImage(0, 0, self.mQImage)
        painter.end()

    def keyPressEvent(self, QKeyEvent):
        super(MyDialog, self).keyPressEvent(QKeyEvent)
        if 's' == QKeyEvent.text():
            cv2.imwrite("cat2.png", self.cvImage)
        else:
            app.exit(1)


if __name__=="__main__":
    import sys
    app = QApplication(sys.argv)
    w = MyDialog()
    w.resize(600, 400)
    w.show()
    app.exec_()