samples/python/snippets/opt_flow.py#

An example to show optical flow in python

  1#!/usr/bin/env python
  2
  3'''
  4example to show optical flow
  5
  6USAGE: opt_flow.py [<video_source>]
  7
  8Keys:
  9 1 - toggle HSV flow visualization
 10 2 - toggle glitch
 11
 12Keys:
 13    ESC    - exit
 14'''
 15
 16# Python 2/3 compatibility
 17from __future__ import print_function
 18
 19import numpy as np
 20import cv2 as cv
 21
 22import video
 23
 24
 25def draw_flow(img, flow, step=16):
 26    h, w = img.shape[:2]
 27    y, x = np.mgrid[step/2:h:step, step/2:w:step].reshape(2,-1).astype(int)
 28    fx, fy = flow[y,x].T
 29    lines = np.vstack([x, y, x+fx, y+fy]).T.reshape(-1, 2, 2)
 30    lines = np.int32(lines + 0.5)
 31    vis = cv.cvtColor(img, cv.COLOR_GRAY2BGR)
 32    cv.polylines(vis, lines, 0, (0, 255, 0))
 33    for (x1, y1), (_x2, _y2) in lines:
 34        cv.circle(vis, (x1, y1), 1, (0, 255, 0), -1)
 35    return vis
 36
 37
 38def draw_hsv(flow):
 39    h, w = flow.shape[:2]
 40    fx, fy = flow[:,:,0], flow[:,:,1]
 41    ang = np.arctan2(fy, fx) + np.pi
 42    v = np.sqrt(fx*fx+fy*fy)
 43    hsv = np.zeros((h, w, 3), np.uint8)
 44    hsv[...,0] = ang*(180/np.pi/2)
 45    hsv[...,1] = 255
 46    hsv[...,2] = np.minimum(v*4, 255)
 47    bgr = cv.cvtColor(hsv, cv.COLOR_HSV2BGR)
 48    return bgr
 49
 50
 51def warp_flow(img, flow):
 52    h, w = flow.shape[:2]
 53    flow = -flow
 54    flow[:,:,0] += np.arange(w)
 55    flow[:,:,1] += np.arange(h)[:,np.newaxis]
 56    res = cv.remap(img, flow, None, cv.INTER_LINEAR)
 57    return res
 58
 59def main():
 60    import sys
 61    try:
 62        fn = sys.argv[1]
 63    except IndexError:
 64        fn = 0
 65
 66    cam = video.create_capture(fn)
 67    _ret, prev = cam.read()
 68    prevgray = cv.cvtColor(prev, cv.COLOR_BGR2GRAY)
 69    show_hsv = False
 70    show_glitch = False
 71    cur_glitch = prev.copy()
 72
 73    while True:
 74        _ret, img = cam.read()
 75        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
 76        flow = cv.calcOpticalFlowFarneback(prevgray, gray, None, 0.5, 3, 15, 3, 5, 1.2, 0)
 77        prevgray = gray
 78
 79        cv.imshow('flow', draw_flow(gray, flow))
 80        if show_hsv:
 81            cv.imshow('flow HSV', draw_hsv(flow))
 82        if show_glitch:
 83            cur_glitch = warp_flow(cur_glitch, flow)
 84            cv.imshow('glitch', cur_glitch)
 85
 86        ch = cv.waitKey(5)
 87        if ch == 27:
 88            break
 89        if ch == ord('1'):
 90            show_hsv = not show_hsv
 91            print('HSV flow visualization is', ['off', 'on'][show_hsv])
 92        if ch == ord('2'):
 93            show_glitch = not show_glitch
 94            if show_glitch:
 95                cur_glitch = img.copy()
 96            print('glitch is', ['off', 'on'][show_glitch])
 97
 98    print('Done')
 99
100
101if __name__ == '__main__':
102    print(__doc__)
103    main()
104    cv.destroyAllWindows()