pyqt5 show numpy arrays in a loop

pyqt5_numpy.py

import sys
import numpy as np
from PyQt5 import QtGui, QtWidgets, QtCore

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super().__init__()
        self.imshow = Grayscale()
        self.setCentralWidget(self.imshow)
        self.update_timer = QtCore.QTimer()
        self.update_timer.timeout.connect(self.on_update)
        self.update_timer.start(100)

    def on_update(self):
        x = np.random.random((100, 100))
        self.imshow.imshow(x)

class Grayscale(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.data = None
        self.imshow(np.random.random((100, 100)))
        self.setGeometry(100, 100, 800, 800)

    def imshow(self, x, vmin=None, vmax=None):
        if vmin is None:
            vmin = x.min()
        if vmax is None:
            vmax = x.max()
        if self.data is None or x.shape != self.data.shape:
            self.data = np.empty((x.shape[0], x.shape[1], 3), dtype=np.uint8)
        x = (255 * (x - vmin) / (vmax - vmin)).astype(np.uint8)
        self.data[:,:,0] = x
        self.data[:,:,1] = x
        self.data[:,:,2] = x
        self.img = QtGui.QImage(self.data.data,
                self.data.shape[0],
                self.data.shape[1],
                3*self.data.shape[1],
                QtGui.QImage.Format_RGB888)
        self.update()

    def paintEvent(self, event):
        geom = self.frameGeometry()
        w, h = geom.width(), geom.height()
        if w < h:
            rect = QtCore.QRect(0, (h - w)//2, w, w)
        else:
            rect = QtCore.QRect((w - h)//2, 0, h, h)
        painter = QtGui.QPainter(self)
        painter.drawImage(rect, self.img)

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    win = MainWindow()
    win.show()
    app.exec_()