Optical flow example - https://www.youtube.com/watch?v=QwmADw_MUig

README.md

Setup

You'll need (preferably) Python 3.6 or greater to run this script. The recommended way to install the requirements is using conda. To do so, you can run the following in your terminal:

# Create a new environment with conda:
conda create --name opt-flow

# Activate the environment
conda activate opt-flow

Install the requirements:

# Install the required packages using pip:
pip install -r requirements.txt

To run the script:

python OpticalFlow.py

To deactivate the environment:

conda deactivate

OpticalFlow.py

# Python 2/3 compatibility
from __future__ import print_function

import numpy as np
import imutils
import cv2
import sys


# Global vars:
WIDTH = 700
STEP = 16
QUIVER = (255, 100, 0)


def draw_flow(img, flow, step=STEP):
    h, w = img.shape[:2]
    y, x = np.mgrid[step/2:h:step, step/2:w:step].reshape(2, -1).astype(int)
    fx, fy = flow[y, x].T
    lines = np.vstack([x, y, x + fx, y + fy]).T.reshape(-1, 2, 2)
    lines = np.int32(lines + 0.5)
    vis = cv2.cvtColor(img, cv2.COLOR_GRAY2BGR)
    cv2.polylines(vis, lines, 0, QUIVER)
    for (x1, y1), (_x2, _y2) in lines:
        cv2.circle(vis, (x1, y1), 1, (0, 255, 0), -1)
    return vis


if __name__ == '__main__':
    try:
        fn = sys.argv[1]
    except IndexError:
        fn = 0

    cam = cv2.VideoCapture(fn)
    ret, prev = cam.read()
    prev = imutils.resize(prev, width=WIDTH)
    prevgray = cv2.cvtColor(prev, cv2.COLOR_BGR2GRAY)

    while True:
        ret, img = cam.read()
        img = imutils.resize(img, width=WIDTH)
        gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
        flow = cv2.calcOpticalFlowFarneback(
            prevgray, gray, None, 0.5, 3, 15, 3, 5, 1.2, 0)
        prevgray = gray

        cv2.imshow('flow', draw_flow(gray, flow))

        ch = cv2.waitKey(5)
        if ch == 27:
            break
    cv2.destroyAllWindows()

requirements.txt

numpy
imutils
opencv-python