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()
105