A quick OpenCV optical (motion) flow example hack

[villares]

# https://docs.opencv.org/4.x/d4/dee/tutorial_optical_flow.html

import py5
import numpy as np
import cv2 # opencv-python

cap = None
py5_img = None
prvs_frame = None
reduced_size = 600, 400

def setup():
    py5.size(600, 400)
    py5.launch_thread(open_capture)

def open_capture():
    global cap, hsv
    cap = cv2.VideoCapture(0)
    print('Capture started')

def draw():
    global py5_img, prvs_frame, flow
    py5.background(255, 255, 0)
    ret = False
    if cap:
        ret, frame = cap.read()  # frame is a numpy array
    if ret:
        frame = cv2.resize(frame, reduced_size)
        next_frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        if prvs_frame is not None:
            flow = cv2.calcOpticalFlowFarneback(prvs_frame, next_frame, None, 0.5, 3, 15, 3, 5, 1.2, 0)
            vmag, vang = cv2.cartToPolar(flow[..., 0], flow[..., 1])
            hsv = np.zeros_like(frame)
            hsv[..., 1] = 255
            hsv[..., 0] = vang * 180 / np.pi / 2 # 0 a 360 / 0 1 / 0 255
            hsv[..., 2] = cv2.normalize(vmag, None, 0, 255, cv2.NORM_MINMAX)
            bgr = cv2.cvtColor(hsv, cv2.COLOR_HSV2BGR)
            py5_img = py5.create_image_from_numpy(bgr, bands='BGR', dst=py5_img)
            py5.image(py5_img, 0, 0)
            draw_direction(flow, 100)
            if vmag.mean() > 1:
                print('moved!')
            else:
                print('')
        prvs_frame = next_frame
 
def exiting():   # py5 will call this for clean up on exit
    cap.release()   

def draw_direction(f, s):
    py5.stroke_weight(5)
    py5.stroke(255)
    hw, hh = py5.width / 2, py5.height / 2 
    py5.line(hw, hh,
             hw + f[... , 0].mean() * s,
             hh + f[... , 1].mean() * s)

py5.run_sketch(block=False)

[Maltiec]

that's great! And I really think that this video itself is a nice work, even without movement vector showing.)

[hx2A]

Nice work! You must have had fun making this!

I do recommend using an exiting() function to close the webcam connection when the Sketch exits. It's cleaner to disconnect properly.

https://py5coding.org/content/user_functions.html#sketch-exiting-event

[villares]

Hmm, I haven't found any mentions on the OpenCV example that I used as reference (link on the first comment) of closing the webcam. Would you have any tips or pointer to the docs of what should I call on exiting()?

[hx2A]

It would be cap.release() for your code. It releases the webcam and makes it available for other processes to use. If you don't release it, sometimes things get tripped up and the next program can't use it and throws weird errors.

[villares]

cool! I'll add it o the example.