pyopencv_motion5_fullcode.py

import cv2
import numpy as np
from PIL import ImageGrab

def motion_detector_gist():

  previous_frame = None

  while True:

    # 1. Load image; convert to RGB
    img_brg = np.array(ImageGrab.grab())
    img_rgb = cv2.cvtColor(src=img_brg, code=cv2.COLOR_BGR2RGB)


    # 2. Prepare image; grayscale and blur
    prepared_frame = cv2.cvtColor(img_rgb, cv2.COLOR_BGR2GRAY)
    prepared_frame = cv2.GaussianBlur(src=prepared_frame, ksize=(5, 5), sigmaX=0)

    # 2. Calculate the difference
    if (previous_frame is None):
      # First frame; there is no previous one yet
      previous_frame = prepared_frame
      continue

    # 3. calculate difference and update previous frame
    diff_frame = cv2.absdiff(src1=previous_frame, src2=prepared_frame)
    previous_frame = prepared_frame

    # 4. Dilute the image a bit to make differences more seeable; more suitable for contour detection
    kernel = np.ones((5, 5))
    diff_frame = cv2.dilate(diff_frame, kernel, 1)

    # 5. Only take different areas that are different enough (>20 / 255)
    thresh_frame = cv2.threshold(src=diff_frame, thresh=20, maxval=255, type=cv2.THRESH_BINARY)[1]

    # 6. Find and optionally draw contours
    contours, _ = cv2.findContours(image=thresh_frame, mode=cv2.RETR_EXTERNAL, method=cv2.CHAIN_APPROX_SIMPLE)
    # Comment below to stop drawing contours
    cv2.drawContours(image=img_rgb, contours=contours, contourIdx=-1, color=(0, 255, 0), thickness=2, lineType=cv2.LINE_AA)
    # Uncomment 6 lines below to stop drawing rectangles
    # for contour in contours:
    #   if cv2.contourArea(contour) < 50:
    #     # too small: skip!
    #       continue
    #   (x, y, w, h) = cv2.boundingRect(contour)
    #   cv2.rectangle(img=img_rgb, pt1=(x, y), pt2=(x + w, y + h), color=(0, 255, 0), thickness=2)

    cv2.imshow('Motion detector', img_rgb)

    if (cv2.waitKey(30) == 27):
      # out.release()
      break

  # Cleanup
  cv2.destroyAllWindows()

if __name__ == "__main__":
  motion_detector_gist()

Thank you @lorenzua02! I've fixed it!

Thanks for the example. FYI, your article still has frame_count and the if statement where prepared_frame can never be reached.