Use Python to save screen shots in array

How do I use python, mss, and opencv to capture my computer screen and save it as an array of images to form a movie? I am converting to gray-scale so it can be a 3 dimensional array. I would like to store each 2d screen shot in a 3d array for viewing and processing. I am having a hard time constructing an array that saves the sequence of screen shots as well as plays back the sequence of screen shots in cv2. Thanks a lot

import time
import numpy as np
import cv2
import mss
from PIL import Image

with mss.mss() as sct:
    fps_list=[]
    matrix_list = []
    monitor = {'top':40, 'left':0, 'width':800, 'height':640}
    timer = 0
    while timer <100:
        last_time = time.time()

        #get raw pizels from screen and save to numpy array
        img = np.array(sct.grab(monitor))
        img=cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

        #Save img data as matrix
        matrix_list[timer,:,:] = img

        #Display Image
        cv2.imshow('Normal', img)
        fps = 1/ (time.time()-last_time)
        fps_list.append(fps)

        #press q to quit
        timer += 1
        if cv2.waitKey(25) & 0xFF == ord('q'):
            cv2.destroyAllWindows()
            break
#calculate fps
fps_list = np.asarray(fps_list)
print(np.average(fps_list))


#playback image movie from screencapture
t=0
while t < 100:
    cv.imshow('Playback',img_matrix[t])
    t += 1

A clue perhaps, save screenshots into a list and replay them later (you will have to adapt the sleep time):

import time
import cv2
import mss
import numpy


with mss.mss() as sct:
    monitor = {'top': 40, 'left': 0, 'width': 800, 'height': 640}
    img_matrix = []

    for _ in range(100):
        # Get raw pizels from screen and save to numpy array
        img = numpy.array(sct.grab(monitor))
        img = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

        # Save img data as matrix
        img_matrix.append(img)

        # Display Image
        cv2.imshow('Normal', img)

        # Press q to quit
        if cv2.waitKey(25) & 0xFF == ord('q'):
            cv2.destroyAllWindows()
            break

    # Playback image movie from screencapture
    for img in img_matrix:
        cv2.imshow('Playback', img)

        # Press q to quit
        if cv2.waitKey(25) & 0xFF == ord('q'):
            cv2.destroyAllWindows()
            break