Merge pull request #25268 from gursimarsingh:samples_cleanup_python

Removed obsolete python samples #25268

Clean Samples #25006 
This PR removes 36 obsolete python samples from the project, as part of an effort to keep the codebase clean and focused on current best practices. Some of these samples will be updated with latest algorithms or will be combined with other existing samples. 

Removed Samples:

> browse.py
camshift.py
coherence.py
color_histogram.py
contours.py
deconvolution.py
dft.py
dis_opt_flow.py
distrans.py
edge.py
feature_homography.py
find_obj.py
fitline.py
gabor_threads.py
hist.py
houghcircles.py
houghlines.py
inpaint.py
kalman.py
kmeans.py
laplace.py
lk_homography.py
lk_track.py
logpolar.py
mosse.py
mser.py
opt_flow.py
plane_ar.py
squares.py
stitching.py
text_skewness_correction.py
texture_flow.py
turing.py
video_threaded.py
video_v4l2.py
watershed.py

These changes aim to improve the repository's clarity and usability by removing examples that are no longer relevant or have been superseded by more up-to-date techniques.

samples/python/snippets/camshift.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python
+
+'''
+Camshift tracker
+================
+
+This is a demo that shows mean-shift based tracking
+You select a color objects such as your face and it tracks it.
+This reads from video camera (0 by default, or the camera number the user enters)
+
+[1] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.14.7673
+
+Usage:
+------
+    camshift.py [<video source>]
+
+    To initialize tracking, select the object with mouse
+
+Keys:
+-----
+    ESC   - exit
+    b     - toggle back-projected probability visualization
+'''
+
+import numpy as np
+import cv2 as cv
+
+# local module
+import video
+from video import presets
+
+
+class App(object):
+    def __init__(self, video_src):
+        self.cam = video.create_capture(video_src, presets['cube'])
+        _ret, self.frame = self.cam.read()
+        cv.namedWindow('camshift')
+        cv.setMouseCallback('camshift', self.onmouse)
+
+        self.selection = None
+        self.drag_start = None
+        self.show_backproj = False
+        self.track_window = None
+
+    def onmouse(self, event, x, y, flags, param):
+        if event == cv.EVENT_LBUTTONDOWN:
+            self.drag_start = (x, y)
+            self.track_window = None
+        if self.drag_start:
+            xmin = min(x, self.drag_start[0])
+            ymin = min(y, self.drag_start[1])
+            xmax = max(x, self.drag_start[0])
+            ymax = max(y, self.drag_start[1])
+            self.selection = (xmin, ymin, xmax, ymax)
+        if event == cv.EVENT_LBUTTONUP:
+            self.drag_start = None
+            self.track_window = (xmin, ymin, xmax - xmin, ymax - ymin)
+
+    def show_hist(self):
+        bin_count = self.hist.shape[0]
+        bin_w = 24
+        img = np.zeros((256, bin_count*bin_w, 3), np.uint8)
+        for i in range(bin_count):
+            h = int(self.hist[i])
+            cv.rectangle(img, (i*bin_w+2, 255), ((i+1)*bin_w-2, 255-h), (int(180.0*i/bin_count), 255, 255), -1)
+        img = cv.cvtColor(img, cv.COLOR_HSV2BGR)
+        cv.imshow('hist', img)
+
+    def run(self):
+        while True:
+            _ret, self.frame = self.cam.read()
+            vis = self.frame.copy()
+            hsv = cv.cvtColor(self.frame, cv.COLOR_BGR2HSV)
+            mask = cv.inRange(hsv, np.array((0., 60., 32.)), np.array((180., 255., 255.)))
+
+            if self.selection:
+                x0, y0, x1, y1 = self.selection
+                hsv_roi = hsv[y0:y1, x0:x1]
+                mask_roi = mask[y0:y1, x0:x1]
+                hist = cv.calcHist( [hsv_roi], [0], mask_roi, [16], [0, 180] )
+                cv.normalize(hist, hist, 0, 255, cv.NORM_MINMAX)
+                self.hist = hist.reshape(-1)
+                self.show_hist()
+
+                vis_roi = vis[y0:y1, x0:x1]
+                cv.bitwise_not(vis_roi, vis_roi)
+                vis[mask == 0] = 0
+
+            if self.track_window and self.track_window[2] > 0 and self.track_window[3] > 0:
+                self.selection = None
+                prob = cv.calcBackProject([hsv], [0], self.hist, [0, 180], 1)
+                prob &= mask
+                term_crit = ( cv.TERM_CRITERIA_EPS | cv.TERM_CRITERIA_COUNT, 10, 1 )
+                track_box, self.track_window = cv.CamShift(prob, self.track_window, term_crit)
+
+                if self.show_backproj:
+                    vis[:] = prob[...,np.newaxis]
+                try:
+                    cv.ellipse(vis, track_box, (0, 0, 255), 2)
+                except:
+                    print(track_box)
+
+            cv.imshow('camshift', vis)
+
+            ch = cv.waitKey(5)
+            if ch == 27:
+                break
+            if ch == ord('b'):
+                self.show_backproj = not self.show_backproj
+        cv.destroyAllWindows()
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    import sys
+    try:
+        video_src = sys.argv[1]
+    except:
+        video_src = 0
+    App(video_src).run()

samples/python/snippets/contours.py

@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+'''
+This program illustrates the use of findContours and drawContours.
+The original image is put up along with the image of drawn contours.
+
+Usage:
+    contours.py
+A trackbar is put up which controls the contour level from -3 to 3
+'''
+
+import numpy as np
+import cv2 as cv
+
+def make_image():
+    img = np.zeros((500, 500), np.uint8)
+    black, white = 0, 255
+    for i in range(6):
+        dx = int((i%2)*250 - 30)
+        dy = int((i/2.)*150)
+
+        if i == 0:
+            for j in range(11):
+                angle = (j+5)*np.pi/21
+                c, s = np.cos(angle), np.sin(angle)
+                x1, y1 = np.int32([dx+100+j*10-80*c, dy+100-90*s])
+                x2, y2 = np.int32([dx+100+j*10-30*c, dy+100-30*s])
+                cv.line(img, (x1, y1), (x2, y2), white)
+
+        cv.ellipse( img, (dx+150, dy+100), (100,70), 0, 0, 360, white, -1 )
+        cv.ellipse( img, (dx+115, dy+70), (30,20), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+185, dy+70), (30,20), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+115, dy+70), (15,15), 0, 0, 360, white, -1 )
+        cv.ellipse( img, (dx+185, dy+70), (15,15), 0, 0, 360, white, -1 )
+        cv.ellipse( img, (dx+115, dy+70), (5,5), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+185, dy+70), (5,5), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+150, dy+100), (10,5), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+150, dy+150), (40,10), 0, 0, 360, black, -1 )
+        cv.ellipse( img, (dx+27, dy+100), (20,35), 0, 0, 360, white, -1 )
+        cv.ellipse( img, (dx+273, dy+100), (20,35), 0, 0, 360, white, -1 )
+    return img
+
+def main():
+    img = make_image()
+    h, w = img.shape[:2]
+
+    contours0, hierarchy = cv.findContours( img.copy(), cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
+    contours = [cv.approxPolyDP(cnt, 3, True) for cnt in contours0]
+
+    def update(levels):
+        vis = np.zeros((h, w, 3), np.uint8)
+        levels = levels - 3
+        cv.drawContours( vis, contours, (-1, 2)[levels <= 0], (128,255,255),
+            3, cv.LINE_AA, hierarchy, abs(levels) )
+        cv.imshow('contours', vis)
+    update(3)
+    cv.createTrackbar( "levels+3", "contours", 3, 7, update )
+    cv.imshow('image', img)
+    cv.waitKey()
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/dft.py

@@ -0,0 +1,120 @@
+#!/usr/bin/env python
+
+'''
+sample for discrete fourier transform (dft)
+
+USAGE:
+    dft.py <image_file>
+'''
+
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import sys
+
+
+def shift_dft(src, dst=None):
+    '''
+        Rearrange the quadrants of Fourier image so that the origin is at
+        the image center. Swaps quadrant 1 with 3, and 2 with 4.
+
+        src and dst arrays must be equal size & type
+    '''
+
+    if dst is None:
+        dst = np.empty(src.shape, src.dtype)
+    elif src.shape != dst.shape:
+        raise ValueError("src and dst must have equal sizes")
+    elif src.dtype != dst.dtype:
+        raise TypeError("src and dst must have equal types")
+
+    if src is dst:
+        ret = np.empty(src.shape, src.dtype)
+    else:
+        ret = dst
+
+    h, w = src.shape[:2]
+
+    cx1 = cx2 = w // 2
+    cy1 = cy2 = h // 2
+
+    # if the size is odd, then adjust the bottom/right quadrants
+    if w % 2 != 0:
+        cx2 += 1
+    if h % 2 != 0:
+        cy2 += 1
+
+    # swap quadrants
+
+    # swap q1 and q3
+    ret[h-cy1:, w-cx1:] = src[0:cy1 , 0:cx1 ]   # q1 -> q3
+    ret[0:cy2 , 0:cx2 ] = src[h-cy2:, w-cx2:]   # q3 -> q1
+
+    # swap q2 and q4
+    ret[0:cy2 , w-cx2:] = src[h-cy2:, 0:cx2 ]   # q2 -> q4
+    ret[h-cy1:, 0:cx1 ] = src[0:cy1 , w-cx1:]   # q4 -> q2
+
+    if src is dst:
+        dst[:,:] = ret
+
+    return dst
+
+
+def main():
+    if len(sys.argv) > 1:
+        fname = sys.argv[1]
+    else:
+        fname = 'baboon.jpg'
+        print("usage : python dft.py <image_file>")
+
+    im = cv.imread(cv.samples.findFile(fname))
+
+    # convert to grayscale
+    im = cv.cvtColor(im, cv.COLOR_BGR2GRAY)
+    h, w = im.shape[:2]
+
+    realInput = im.astype(np.float64)
+
+    # perform an optimally sized dft
+    dft_M = cv.getOptimalDFTSize(w)
+    dft_N = cv.getOptimalDFTSize(h)
+
+    # copy A to dft_A and pad dft_A with zeros
+    dft_A = np.zeros((dft_N, dft_M, 2), dtype=np.float64)
+    dft_A[:h, :w, 0] = realInput
+
+    # no need to pad bottom part of dft_A with zeros because of
+    # use of nonzeroRows parameter in cv.dft()
+    cv.dft(dft_A, dst=dft_A, nonzeroRows=h)
+
+    cv.imshow("win", im)
+
+    # Split fourier into real and imaginary parts
+    image_Re, image_Im = cv.split(dft_A)
+
+    # Compute the magnitude of the spectrum Mag = sqrt(Re^2 + Im^2)
+    magnitude = cv.sqrt(image_Re**2.0 + image_Im**2.0)
+
+    # Compute log(1 + Mag)
+    log_spectrum = cv.log(1.0 + magnitude)
+
+    # Rearrange the quadrants of Fourier image so that the origin is at
+    # the image center
+    shift_dft(log_spectrum, log_spectrum)
+
+    # normalize and display the results as rgb
+    cv.normalize(log_spectrum, log_spectrum, 0.0, 1.0, cv.NORM_MINMAX)
+    cv.imshow("magnitude", log_spectrum)
+
+    cv.waitKey(0)
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/dis_opt_flow.py

@@ -0,0 +1,122 @@
+#!/usr/bin/env python
+
+'''
+example to show optical flow estimation using DISOpticalFlow
+
+USAGE: dis_opt_flow.py [<video_source>]
+
+Keys:
+ 1  - toggle HSV flow visualization
+ 2  - toggle glitch
+ 3  - toggle spatial propagation of flow vectors
+ 4  - toggle temporal propagation of flow vectors
+ESC - exit
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import video
+
+
+def draw_flow(img, flow, step=16):
+    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 = cv.cvtColor(img, cv.COLOR_GRAY2BGR)
+    cv.polylines(vis, lines, 0, (0, 255, 0))
+    for (x1, y1), (_x2, _y2) in lines:
+        cv.circle(vis, (x1, y1), 1, (0, 255, 0), -1)
+    return vis
+
+
+def draw_hsv(flow):
+    h, w = flow.shape[:2]
+    fx, fy = flow[:,:,0], flow[:,:,1]
+    ang = np.arctan2(fy, fx) + np.pi
+    v = np.sqrt(fx*fx+fy*fy)
+    hsv = np.zeros((h, w, 3), np.uint8)
+    hsv[...,0] = ang*(180/np.pi/2)
+    hsv[...,1] = 255
+    hsv[...,2] = np.minimum(v*4, 255)
+    bgr = cv.cvtColor(hsv, cv.COLOR_HSV2BGR)
+    return bgr
+
+
+def warp_flow(img, flow):
+    h, w = flow.shape[:2]
+    flow = -flow
+    flow[:,:,0] += np.arange(w)
+    flow[:,:,1] += np.arange(h)[:,np.newaxis]
+    res = cv.remap(img, flow, None, cv.INTER_LINEAR)
+    return res
+
+
+def main():
+    import sys
+    print(__doc__)
+    try:
+        fn = sys.argv[1]
+    except IndexError:
+        fn = 0
+
+    cam = video.create_capture(fn)
+    _ret, prev = cam.read()
+    prevgray = cv.cvtColor(prev, cv.COLOR_BGR2GRAY)
+    show_hsv = False
+    show_glitch = False
+    use_spatial_propagation = False
+    use_temporal_propagation = True
+    cur_glitch = prev.copy()
+    inst = cv.DISOpticalFlow.create(cv.DISOPTICAL_FLOW_PRESET_MEDIUM)
+    inst.setUseSpatialPropagation(use_spatial_propagation)
+
+    flow = None
+    while True:
+        _ret, img = cam.read()
+        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+        if flow is not None and use_temporal_propagation:
+            #warp previous flow to get an initial approximation for the current flow:
+            flow = inst.calc(prevgray, gray, warp_flow(flow,flow))
+        else:
+            flow = inst.calc(prevgray, gray, None)
+        prevgray = gray
+
+        cv.imshow('flow', draw_flow(gray, flow))
+        if show_hsv:
+            cv.imshow('flow HSV', draw_hsv(flow))
+        if show_glitch:
+            cur_glitch = warp_flow(cur_glitch, flow)
+            cv.imshow('glitch', cur_glitch)
+
+        ch = 0xFF & cv.waitKey(5)
+        if ch == 27:
+            break
+        if ch == ord('1'):
+            show_hsv = not show_hsv
+            print('HSV flow visualization is', ['off', 'on'][show_hsv])
+        if ch == ord('2'):
+            show_glitch = not show_glitch
+            if show_glitch:
+                cur_glitch = img.copy()
+            print('glitch is', ['off', 'on'][show_glitch])
+        if ch == ord('3'):
+            use_spatial_propagation = not use_spatial_propagation
+            inst.setUseSpatialPropagation(use_spatial_propagation)
+            print('spatial propagation is', ['off', 'on'][use_spatial_propagation])
+        if ch == ord('4'):
+            use_temporal_propagation = not use_temporal_propagation
+            print('temporal propagation is', ['off', 'on'][use_temporal_propagation])
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/distrans.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python
+
+'''
+Distance transform sample.
+
+Usage:
+  distrans.py [<image>]
+
+Keys:
+  ESC   - exit
+  v     - toggle voronoi mode
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+from common import make_cmap
+
+def main():
+    import sys
+    try:
+        fn = sys.argv[1]
+    except:
+        fn = 'fruits.jpg'
+
+    fn = cv.samples.findFile(fn)
+    img = cv.imread(fn, cv.IMREAD_GRAYSCALE)
+    if img is None:
+        print('Failed to load fn:', fn)
+        sys.exit(1)
+
+    cm = make_cmap('jet')
+    need_update = True
+    voronoi = False
+
+    def update(dummy=None):
+        global need_update
+        need_update = False
+        thrs = cv.getTrackbarPos('threshold', 'distrans')
+        mark = cv.Canny(img, thrs, 3*thrs)
+        dist, labels = cv.distanceTransformWithLabels(~mark, cv.DIST_L2, 5)
+        if voronoi:
+            vis = cm[np.uint8(labels)]
+        else:
+            vis = cm[np.uint8(dist*2)]
+        vis[mark != 0] = 255
+        cv.imshow('distrans', vis)
+
+    def invalidate(dummy=None):
+        global need_update
+        need_update = True
+
+    cv.namedWindow('distrans')
+    cv.createTrackbar('threshold', 'distrans', 60, 255, invalidate)
+    update()
+
+
+    while True:
+        ch = cv.waitKey(50)
+        if ch == 27:
+            break
+        if ch == ord('v'):
+            voronoi = not voronoi
+            print('showing', ['distance', 'voronoi'][voronoi])
+            update()
+        if need_update:
+            update()
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/fitline.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python
+
+'''
+Robust line fitting.
+==================
+
+Example of using cv.fitLine function for fitting line
+to points in presence of outliers.
+
+Usage
+-----
+fitline.py
+
+Switch through different M-estimator functions and see,
+how well the robust functions fit the line even
+in case of ~50% of outliers.
+
+Keys
+----
+SPACE - generate random points
+f     - change distance function
+ESC   - exit
+'''
+
+import numpy as np
+import cv2 as cv
+
+# built-in modules
+import itertools as it
+
+# local modules
+from common import draw_str
+
+
+w, h = 512, 256
+
+def toint(p):
+    return tuple(map(int, p))
+
+def sample_line(p1, p2, n, noise=0.0):
+    p1 = np.float32(p1)
+    t = np.random.rand(n,1)
+    return p1 + (p2-p1)*t + np.random.normal(size=(n, 2))*noise
+
+dist_func_names = it.cycle('DIST_L2 DIST_L1 DIST_L12 DIST_FAIR DIST_WELSCH DIST_HUBER'.split())
+
+cur_func_name = next(dist_func_names)
+
+def update(_=None):
+    noise = cv.getTrackbarPos('noise', 'fit line')
+    n = cv.getTrackbarPos('point n', 'fit line')
+    r = cv.getTrackbarPos('outlier %', 'fit line') / 100.0
+    outn = int(n*r)
+
+    p0, p1 = (90, 80), (w-90, h-80)
+    img = np.zeros((h, w, 3), np.uint8)
+    cv.line(img, toint(p0), toint(p1), (0, 255, 0))
+
+    if n > 0:
+        line_points = sample_line(p0, p1, n-outn, noise)
+        outliers = np.random.rand(outn, 2) * (w, h)
+        points = np.vstack([line_points, outliers])
+        for p in line_points:
+            cv.circle(img, toint(p), 2, (255, 255, 255), -1)
+        for p in outliers:
+            cv.circle(img, toint(p), 2, (64, 64, 255), -1)
+        func = getattr(cv, cur_func_name)
+        vx, vy, cx, cy = cv.fitLine(np.float32(points), func, 0, 0.01, 0.01)
+        cv.line(img, (int(cx-vx*w), int(cy-vy*w)), (int(cx+vx*w), int(cy+vy*w)), (0, 0, 255))
+
+    draw_str(img, (20, 20), cur_func_name)
+    cv.imshow('fit line', img)
+
+def main():
+    cv.namedWindow('fit line')
+    cv.createTrackbar('noise', 'fit line', 3, 50, update)
+    cv.createTrackbar('point n', 'fit line', 100, 500, update)
+    cv.createTrackbar('outlier %', 'fit line', 30, 100, update)
+    while True:
+        update()
+        ch = cv.waitKey(0)
+        if ch == ord('f'):
+            global cur_func_name
+            cur_func_name = next(dist_func_names)
+        if ch == 27:
+            break
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/houghcircles.py

@@ -0,0 +1,49 @@
+#!/usr/bin/python
+
+'''
+This example illustrates how to use cv.HoughCircles() function.
+
+Usage:
+    houghcircles.py [<image_name>]
+    image argument defaults to board.jpg
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import sys
+
+def main():
+    try:
+        fn = sys.argv[1]
+    except IndexError:
+        fn = 'board.jpg'
+
+    src = cv.imread(cv.samples.findFile(fn))
+    img = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
+    img = cv.medianBlur(img, 5)
+    cimg = src.copy() # numpy function
+
+    circles = cv.HoughCircles(img, cv.HOUGH_GRADIENT, 1, 10, np.array([]), 100, 30, 1, 30)
+
+    if circles is not None: # Check if circles have been found and only then iterate over these and add them to the image
+        circles = np.uint16(np.around(circles))
+        _a, b, _c = circles.shape
+        for i in range(b):
+            cv.circle(cimg, (circles[0][i][0], circles[0][i][1]), circles[0][i][2], (0, 0, 255), 3, cv.LINE_AA)
+            cv.circle(cimg, (circles[0][i][0], circles[0][i][1]), 2, (0, 255, 0), 3, cv.LINE_AA)  # draw center of circle
+
+        cv.imshow("detected circles", cimg)
+
+    cv.imshow("source", src)
+    cv.waitKey(0)
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/houghlines.py

@@ -0,0 +1,60 @@
+#!/usr/bin/python
+
+'''
+This example illustrates how to use Hough Transform to find lines
+
+Usage:
+    houghlines.py [<image_name>]
+    image argument defaults to pic1.png
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import cv2 as cv
+import numpy as np
+
+import sys
+import math
+
+def main():
+    try:
+        fn = sys.argv[1]
+    except IndexError:
+        fn = 'pic1.png'
+
+    src = cv.imread(cv.samples.findFile(fn))
+    dst = cv.Canny(src, 50, 200)
+    cdst = cv.cvtColor(dst, cv.COLOR_GRAY2BGR)
+
+    if True: # HoughLinesP
+        lines = cv.HoughLinesP(dst, 1, math.pi/180.0, 40, np.array([]), 50, 10)
+        a, b, _c = lines.shape
+        for i in range(a):
+            cv.line(cdst, (lines[i][0][0], lines[i][0][1]), (lines[i][0][2], lines[i][0][3]), (0, 0, 255), 3, cv.LINE_AA)
+
+    else:    # HoughLines
+        lines = cv.HoughLines(dst, 1, math.pi/180.0, 50, np.array([]), 0, 0)
+        if lines is not None:
+            a, b, _c = lines.shape
+            for i in range(a):
+                rho = lines[i][0][0]
+                theta = lines[i][0][1]
+                a = math.cos(theta)
+                b = math.sin(theta)
+                x0, y0 = a*rho, b*rho
+                pt1 = ( int(x0+1000*(-b)), int(y0+1000*(a)) )
+                pt2 = ( int(x0-1000*(-b)), int(y0-1000*(a)) )
+                cv.line(cdst, pt1, pt2, (0, 0, 255), 3, cv.LINE_AA)
+
+    cv.imshow("detected lines", cdst)
+
+    cv.imshow("source", src)
+    cv.waitKey(0)
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/kalman.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python
+"""
+   Tracking of rotating point.
+   Point moves in a circle and is characterized by a 1D state.
+   state_k+1 = state_k + speed + process_noise N(0, 1e-5)
+   The speed is constant.
+   Both state and measurements vectors are 1D (a point angle),
+   Measurement is the real state + gaussian noise N(0, 1e-1).
+   The real and the measured points are connected with red line segment,
+   the real and the estimated points are connected with yellow line segment,
+   the real and the corrected estimated points are connected with green line segment.
+   (if Kalman filter works correctly,
+    the yellow segment should be shorter than the red one and
+    the green segment should be shorter than the yellow one).
+   Pressing any key (except ESC) will reset the tracking.
+   Pressing ESC will stop the program.
+"""
+
+import numpy as np
+import cv2 as cv
+
+from math import cos, sin, sqrt, pi
+
+def main():
+    img_height = 500
+    img_width = 500
+    kalman = cv.KalmanFilter(2, 1, 0)
+
+    code = -1
+    num_circle_steps = 12
+    while True:
+        img = np.zeros((img_height, img_width, 3), np.uint8)
+        state = np.array([[0.0],[(2 * pi) / num_circle_steps]])   # start state
+        kalman.transitionMatrix = np.array([[1., 1.], [0., 1.]])  # F. input
+        kalman.measurementMatrix = 1. * np.eye(1, 2)              # H. input
+        kalman.processNoiseCov = 1e-5 * np.eye(2)                 # Q. input
+        kalman.measurementNoiseCov = 1e-1 * np.ones((1, 1))       # R. input
+        kalman.errorCovPost = 1. * np.eye(2, 2)                   # P._k|k  KF state var
+        kalman.statePost = 0.1 * np.random.randn(2, 1)            # x^_k|k  KF state var
+
+        while True:
+            def calc_point(angle):
+                return (np.around(img_width / 2. + img_width / 3.0 * cos(angle), 0).astype(int),
+                        np.around(img_height / 2. - img_width / 3.0 * sin(angle), 1).astype(int))
+            img = img * 1e-3
+            state_angle = state[0, 0]
+            state_pt = calc_point(state_angle)
+            # advance Kalman filter to next timestep
+            # updates statePre, statePost, errorCovPre, errorCovPost
+            # k-> k+1, x'(k) = A*x(k)
+            # P'(k) = temp1*At + Q
+            prediction = kalman.predict()
+
+            predict_pt = calc_point(prediction[0, 0])  # equivalent to calc_point(kalman.statePre[0,0])
+            # generate measurement
+            measurement = kalman.measurementNoiseCov * np.random.randn(1, 1)
+            measurement = np.dot(kalman.measurementMatrix, state) + measurement
+
+            measurement_angle = measurement[0, 0]
+            measurement_pt = calc_point(measurement_angle)
+
+            # correct the state estimates based on measurements
+            # updates statePost & errorCovPost
+            kalman.correct(measurement)
+            improved_pt = calc_point(kalman.statePost[0, 0])
+
+            # plot points
+            cv.drawMarker(img, measurement_pt, (0, 0, 255), cv.MARKER_SQUARE, 5, 2)
+            cv.drawMarker(img, predict_pt, (0, 255, 255), cv.MARKER_SQUARE, 5, 2)
+            cv.drawMarker(img, improved_pt, (0, 255, 0), cv.MARKER_SQUARE, 5, 2)
+            cv.drawMarker(img, state_pt, (255, 255, 255), cv.MARKER_STAR, 10, 1)
+            # forecast one step
+            cv.drawMarker(img, calc_point(np.dot(kalman.transitionMatrix, kalman.statePost)[0, 0]),
+                          (255, 255, 0), cv.MARKER_SQUARE, 12, 1)
+
+            cv.line(img, state_pt, measurement_pt, (0, 0, 255), 1, cv.LINE_AA, 0)  # red measurement error
+            cv.line(img, state_pt, predict_pt, (0, 255, 255), 1, cv.LINE_AA, 0)  # yellow pre-meas error
+            cv.line(img, state_pt, improved_pt, (0, 255, 0), 1, cv.LINE_AA, 0)  # green post-meas error
+
+            # update the real process
+            process_noise = sqrt(kalman.processNoiseCov[0, 0]) * np.random.randn(2, 1)
+            state = np.dot(kalman.transitionMatrix, state) + process_noise  # x_k+1 = F x_k + w_k
+
+            cv.imshow("Kalman", img)
+            code = cv.waitKey(1000)
+            if code != -1:
+                break
+
+        if code in [27, ord('q'), ord('Q')]:
+            break
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/kmeans.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+
+'''
+K-means clusterization sample.
+Usage:
+   kmeans.py
+
+Keyboard shortcuts:
+   ESC   - exit
+   space - generate new distribution
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+from gaussian_mix import make_gaussians
+
+def main():
+    cluster_n = 5
+    img_size = 512
+
+    # generating bright palette
+    colors = np.zeros((1, cluster_n, 3), np.uint8)
+    colors[0,:] = 255
+    colors[0,:,0] = np.arange(0, 180, 180.0/cluster_n)
+    colors = cv.cvtColor(colors, cv.COLOR_HSV2BGR)[0]
+
+    while True:
+        print('sampling distributions...')
+        points, _ = make_gaussians(cluster_n, img_size)
+
+        term_crit = (cv.TERM_CRITERIA_EPS, 30, 0.1)
+        _ret, labels, _centers = cv.kmeans(points, cluster_n, None, term_crit, 10, 0)
+
+        img = np.zeros((img_size, img_size, 3), np.uint8)
+        for (x, y), label in zip(np.int32(points), labels.ravel()):
+            c = list(map(int, colors[label]))
+
+            cv.circle(img, (x, y), 1, c, -1)
+
+        cv.imshow('kmeans', img)
+        ch = cv.waitKey(0)
+        if ch == 27:
+            break
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/laplace.py

@@ -0,0 +1,69 @@
+#!/usr/bin/env python
+
+'''
+    This program demonstrates Laplace point/edge detection using
+    OpenCV function Laplacian()
+    It captures from the camera of your choice: 0, 1, ... default 0
+    Usage:
+        python laplace.py <ddepth> <smoothType> <sigma>
+        If no arguments given default arguments will be used.
+
+    Keyboard Shortcuts:
+    Press space bar to exit the program.
+    '''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+import sys
+
+def main():
+    # Declare the variables we are going to use
+    ddepth = cv.CV_16S
+    smoothType = "MedianBlur"
+    sigma = 3
+    if len(sys.argv)==4:
+        ddepth = sys.argv[1]
+        smoothType = sys.argv[2]
+        sigma = sys.argv[3]
+    # Taking input from the camera
+    cap=cv.VideoCapture(0)
+    # Create Window and Trackbar
+    cv.namedWindow("Laplace of Image", cv.WINDOW_AUTOSIZE)
+    cv.createTrackbar("Kernel Size Bar", "Laplace of Image", sigma, 15, lambda x:x)
+    # Printing frame width, height and FPS
+    print("=="*40)
+    print("Frame Width: ", cap.get(cv.CAP_PROP_FRAME_WIDTH), "Frame Height: ", cap.get(cv.CAP_PROP_FRAME_HEIGHT), "FPS: ", cap.get(cv.CAP_PROP_FPS))
+    while True:
+        # Reading input from the camera
+        ret, frame = cap.read()
+        if ret == False:
+            print("Can't open camera/video stream")
+            break
+        # Taking input/position from the trackbar
+        sigma = cv.getTrackbarPos("Kernel Size Bar", "Laplace of Image")
+        # Setting kernel size
+        ksize = (sigma*5)|1
+        # Removing noise by blurring with a filter
+        if smoothType == "GAUSSIAN":
+            smoothed = cv.GaussianBlur(frame, (ksize, ksize), sigma, sigma)
+        if smoothType == "BLUR":
+            smoothed = cv.blur(frame, (ksize, ksize))
+        if smoothType == "MedianBlur":
+            smoothed = cv.medianBlur(frame, ksize)
+
+        # Apply Laplace function
+        laplace = cv.Laplacian(smoothed, ddepth, 5)
+        # Converting back to uint8
+        result = cv.convertScaleAbs(laplace, (sigma+1)*0.25)
+        # Display Output
+        cv.imshow("Laplace of Image", result)
+        k = cv.waitKey(30)
+        if k == 27:
+            return
+if __name__ == "__main__":
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/lk_track.py

@@ -0,0 +1,106 @@
+#!/usr/bin/env python
+
+'''
+Lucas-Kanade tracker
+====================
+
+Lucas-Kanade sparse optical flow demo. Uses goodFeaturesToTrack
+for track initialization and back-tracking for match verification
+between frames.
+
+Usage
+-----
+lk_track.py [<video_source>]
+
+
+Keys
+----
+ESC - exit
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import video
+from common import anorm2, draw_str
+
+lk_params = dict( winSize  = (15, 15),
+                  maxLevel = 2,
+                  criteria = (cv.TERM_CRITERIA_EPS | cv.TERM_CRITERIA_COUNT, 10, 0.03))
+
+feature_params = dict( maxCorners = 500,
+                       qualityLevel = 0.3,
+                       minDistance = 7,
+                       blockSize = 7 )
+
+class App:
+    def __init__(self, video_src):
+        self.track_len = 10
+        self.detect_interval = 5
+        self.tracks = []
+        self.cam = video.create_capture(video_src)
+        self.frame_idx = 0
+
+    def run(self):
+        while True:
+            _ret, frame = self.cam.read()
+            frame_gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
+            vis = frame.copy()
+
+            if len(self.tracks) > 0:
+                img0, img1 = self.prev_gray, frame_gray
+                p0 = np.float32([tr[-1] for tr in self.tracks]).reshape(-1, 1, 2)
+                p1, _st, _err = cv.calcOpticalFlowPyrLK(img0, img1, p0, None, **lk_params)
+                p0r, _st, _err = cv.calcOpticalFlowPyrLK(img1, img0, p1, None, **lk_params)
+                d = abs(p0-p0r).reshape(-1, 2).max(-1)
+                good = d < 1
+                new_tracks = []
+                for tr, (x, y), good_flag in zip(self.tracks, p1.reshape(-1, 2), good):
+                    if not good_flag:
+                        continue
+                    tr.append((x, y))
+                    if len(tr) > self.track_len:
+                        del tr[0]
+                    new_tracks.append(tr)
+                    cv.circle(vis, (int(x), int(y)), 2, (0, 255, 0), -1)
+                self.tracks = new_tracks
+                cv.polylines(vis, [np.int32(tr) for tr in self.tracks], False, (0, 255, 0))
+                draw_str(vis, (20, 20), 'track count: %d' % len(self.tracks))
+
+            if self.frame_idx % self.detect_interval == 0:
+                mask = np.zeros_like(frame_gray)
+                mask[:] = 255
+                for x, y in [np.int32(tr[-1]) for tr in self.tracks]:
+                    cv.circle(mask, (x, y), 5, 0, -1)
+                p = cv.goodFeaturesToTrack(frame_gray, mask = mask, **feature_params)
+                if p is not None:
+                    for x, y in np.float32(p).reshape(-1, 2):
+                        self.tracks.append([(x, y)])
+
+
+            self.frame_idx += 1
+            self.prev_gray = frame_gray
+            cv.imshow('lk_track', vis)
+
+            ch = cv.waitKey(1)
+            if ch == 27:
+                break
+
+def main():
+    import sys
+    try:
+        video_src = sys.argv[1]
+    except:
+        video_src = 0
+
+    App(video_src).run()
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/logpolar.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+'''
+plots image as logPolar and linearPolar
+
+Usage:
+    logpolar.py
+
+Keys:
+    ESC    - exit
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+def main():
+    import sys
+    try:
+        fn = sys.argv[1]
+    except IndexError:
+        fn = 'fruits.jpg'
+
+    img = cv.imread(cv.samples.findFile(fn))
+    if img is None:
+        print('Failed to load image file:', fn)
+        sys.exit(1)
+
+    img2 = cv.logPolar(img, (img.shape[0]/2, img.shape[1]/2), 40, cv.WARP_FILL_OUTLIERS)
+    img3 = cv.linearPolar(img, (img.shape[0]/2, img.shape[1]/2), 40, cv.WARP_FILL_OUTLIERS)
+
+    cv.imshow('before', img)
+    cv.imshow('logpolar', img2)
+    cv.imshow('linearpolar', img3)
+
+    cv.waitKey(0)
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/mser.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+'''
+MSER detector demo
+==================
+
+Usage:
+------
+    mser.py [<video source>]
+
+Keys:
+-----
+    ESC   - exit
+
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import video
+import sys
+
+def main():
+    try:
+        video_src = sys.argv[1]
+    except:
+        video_src = 0
+
+    cam = video.create_capture(video_src)
+    mser = cv.MSER_create()
+
+    while True:
+        ret, img = cam.read()
+        if ret == 0:
+            break
+        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+        vis = img.copy()
+
+        regions, _ = mser.detectRegions(gray)
+        hulls = [cv.convexHull(p.reshape(-1, 1, 2)) for p in regions]
+        cv.polylines(vis, hulls, 1, (0, 255, 0))
+
+        cv.imshow('img', vis)
+        if cv.waitKey(5) == 27:
+            break
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/opt_flow.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python
+
+'''
+example to show optical flow
+
+USAGE: opt_flow.py [<video_source>]
+
+Keys:
+ 1 - toggle HSV flow visualization
+ 2 - toggle glitch
+
+Keys:
+    ESC    - exit
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import video
+
+
+def draw_flow(img, flow, step=16):
+    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 = cv.cvtColor(img, cv.COLOR_GRAY2BGR)
+    cv.polylines(vis, lines, 0, (0, 255, 0))
+    for (x1, y1), (_x2, _y2) in lines:
+        cv.circle(vis, (x1, y1), 1, (0, 255, 0), -1)
+    return vis
+
+
+def draw_hsv(flow):
+    h, w = flow.shape[:2]
+    fx, fy = flow[:,:,0], flow[:,:,1]
+    ang = np.arctan2(fy, fx) + np.pi
+    v = np.sqrt(fx*fx+fy*fy)
+    hsv = np.zeros((h, w, 3), np.uint8)
+    hsv[...,0] = ang*(180/np.pi/2)
+    hsv[...,1] = 255
+    hsv[...,2] = np.minimum(v*4, 255)
+    bgr = cv.cvtColor(hsv, cv.COLOR_HSV2BGR)
+    return bgr
+
+
+def warp_flow(img, flow):
+    h, w = flow.shape[:2]
+    flow = -flow
+    flow[:,:,0] += np.arange(w)
+    flow[:,:,1] += np.arange(h)[:,np.newaxis]
+    res = cv.remap(img, flow, None, cv.INTER_LINEAR)
+    return res
+
+def main():
+    import sys
+    try:
+        fn = sys.argv[1]
+    except IndexError:
+        fn = 0
+
+    cam = video.create_capture(fn)
+    _ret, prev = cam.read()
+    prevgray = cv.cvtColor(prev, cv.COLOR_BGR2GRAY)
+    show_hsv = False
+    show_glitch = False
+    cur_glitch = prev.copy()
+
+    while True:
+        _ret, img = cam.read()
+        gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+        flow = cv.calcOpticalFlowFarneback(prevgray, gray, None, 0.5, 3, 15, 3, 5, 1.2, 0)
+        prevgray = gray
+
+        cv.imshow('flow', draw_flow(gray, flow))
+        if show_hsv:
+            cv.imshow('flow HSV', draw_hsv(flow))
+        if show_glitch:
+            cur_glitch = warp_flow(cur_glitch, flow)
+            cv.imshow('glitch', cur_glitch)
+
+        ch = cv.waitKey(5)
+        if ch == 27:
+            break
+        if ch == ord('1'):
+            show_hsv = not show_hsv
+            print('HSV flow visualization is', ['off', 'on'][show_hsv])
+        if ch == ord('2'):
+            show_glitch = not show_glitch
+            if show_glitch:
+                cur_glitch = img.copy()
+            print('glitch is', ['off', 'on'][show_glitch])
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/squares.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+
+'''
+Simple "Square Detector" program.
+
+Loads several images sequentially and tries to find squares in each image.
+'''
+
+import numpy as np
+import cv2 as cv
+
+
+def angle_cos(p0, p1, p2):
+    d1, d2 = (p0-p1).astype('float'), (p2-p1).astype('float')
+    return abs( np.dot(d1, d2) / np.sqrt( np.dot(d1, d1)*np.dot(d2, d2) ) )
+
+def find_squares(img):
+    img = cv.GaussianBlur(img, (5, 5), 0)
+    squares = []
+    for gray in cv.split(img):
+        for thrs in range(0, 255, 26):
+            if thrs == 0:
+                bin = cv.Canny(gray, 0, 50, apertureSize=5)
+                bin = cv.dilate(bin, None)
+            else:
+                _retval, bin = cv.threshold(gray, thrs, 255, cv.THRESH_BINARY)
+            contours, _hierarchy = cv.findContours(bin, cv.RETR_LIST, cv.CHAIN_APPROX_SIMPLE)
+            for cnt in contours:
+                cnt_len = cv.arcLength(cnt, True)
+                cnt = cv.approxPolyDP(cnt, 0.02*cnt_len, True)
+                if len(cnt) == 4 and cv.contourArea(cnt) > 1000 and cv.isContourConvex(cnt):
+                    cnt = cnt.reshape(-1, 2)
+                    max_cos = np.max([angle_cos( cnt[i], cnt[(i+1) % 4], cnt[(i+2) % 4] ) for i in range(4)])
+                    if max_cos < 0.1:
+                        squares.append(cnt)
+    return squares
+
+def main():
+    from glob import glob
+    for fn in glob('../data/pic*.png'):
+        img = cv.imread(fn)
+        squares = find_squares(img)
+        cv.drawContours( img, squares, -1, (0, 255, 0), 3 )
+        cv.imshow('squares', img)
+        ch = cv.waitKey()
+        if ch == 27:
+            break
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/stitching.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python
+
+'''
+Stitching sample
+================
+
+Show how to use Stitcher API from python in a simple way to stitch panoramas
+or scans.
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+import argparse
+import sys
+
+modes = (cv.Stitcher_PANORAMA, cv.Stitcher_SCANS)
+
+parser = argparse.ArgumentParser(prog='stitching.py', description='Stitching sample.')
+parser.add_argument('--mode',
+    type = int, choices = modes, default = cv.Stitcher_PANORAMA,
+    help = 'Determines configuration of stitcher. The default is `PANORAMA` (%d), '
+         'mode suitable for creating photo panoramas. Option `SCANS` (%d) is suitable '
+         'for stitching materials under affine transformation, such as scans.' % modes)
+parser.add_argument('--output', default = 'result.jpg',
+    help = 'Resulting image. The default is `result.jpg`.')
+parser.add_argument('img', nargs='+', help = 'input images')
+
+__doc__ += '\n' + parser.format_help()
+
+def main():
+    args = parser.parse_args()
+
+    # read input images
+    imgs = []
+    for img_name in args.img:
+        img = cv.imread(cv.samples.findFile(img_name))
+        if img is None:
+            print("can't read image " + img_name)
+            sys.exit(-1)
+        imgs.append(img)
+
+    stitcher = cv.Stitcher.create(args.mode)
+    status, pano = stitcher.stitch(imgs)
+
+    if status != cv.Stitcher_OK:
+        print("Can't stitch images, error code = %d" % status)
+        sys.exit(-1)
+
+    cv.imwrite(args.output, pano)
+    print("stitching completed successfully. %s saved!" % args.output)
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/texture_flow.py

@@ -0,0 +1,55 @@
+#!/usr/bin/env python
+
+'''
+Texture flow direction estimation.
+
+Sample shows how cv.cornerEigenValsAndVecs function can be used
+to estimate image texture flow direction.
+
+Usage:
+    texture_flow.py [<image>]
+'''
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+
+def main():
+    import sys
+    try:
+        fn = sys.argv[1]
+    except:
+        fn = 'starry_night.jpg'
+
+    img = cv.imread(cv.samples.findFile(fn))
+    if img is None:
+        print('Failed to load image file:', fn)
+        sys.exit(1)
+
+    gray = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+    h, w = img.shape[:2]
+
+    eigen = cv.cornerEigenValsAndVecs(gray, 15, 3)
+    eigen = eigen.reshape(h, w, 3, 2)  # [[e1, e2], v1, v2]
+    flow = eigen[:,:,2]
+
+    vis = img.copy()
+    vis[:] = (192 + np.uint32(vis)) / 2
+    d = 12
+    points =  np.dstack( np.mgrid[d/2:w:d, d/2:h:d] ).reshape(-1, 2)
+    for x, y in np.int32(points):
+        vx, vy = np.int32(flow[y, x]*d)
+        cv.line(vis, (x-vx, y-vy), (x+vx, y+vy), (0, 0, 0), 1, cv.LINE_AA)
+    cv.imshow('input', img)
+    cv.imshow('flow', vis)
+    cv.waitKey()
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    main()
+    cv.destroyAllWindows()

samples/python/snippets/watershed.py

@@ -0,0 +1,85 @@
+#!/usr/bin/env python
+
+'''
+Watershed segmentation
+=========
+
+This program demonstrates the watershed segmentation algorithm
+in OpenCV: watershed().
+
+Usage
+-----
+watershed.py [image filename]
+
+Keys
+----
+  1-7   - switch marker color
+  SPACE - update segmentation
+  r     - reset
+  a     - toggle autoupdate
+  ESC   - exit
+
+'''
+
+
+# Python 2/3 compatibility
+from __future__ import print_function
+
+import numpy as np
+import cv2 as cv
+from common import Sketcher
+
+class App:
+    def __init__(self, fn):
+        self.img = cv.imread(fn)
+        if self.img is None:
+            raise Exception('Failed to load image file: %s' % fn)
+
+        h, w = self.img.shape[:2]
+        self.markers = np.zeros((h, w), np.int32)
+        self.markers_vis = self.img.copy()
+        self.cur_marker = 1
+        self.colors = np.int32( list(np.ndindex(2, 2, 2)) ) * 255
+
+        self.auto_update = True
+        self.sketch = Sketcher('img', [self.markers_vis, self.markers], self.get_colors)
+
+    def get_colors(self):
+        return list(map(int, self.colors[self.cur_marker])), self.cur_marker
+
+    def watershed(self):
+        m = self.markers.copy()
+        cv.watershed(self.img, m)
+        overlay = self.colors[np.maximum(m, 0)]
+        vis = cv.addWeighted(self.img, 0.5, overlay, 0.5, 0.0, dtype=cv.CV_8UC3)
+        cv.imshow('watershed', vis)
+
+    def run(self):
+        while cv.getWindowProperty('img', 0) != -1 or cv.getWindowProperty('watershed', 0) != -1:
+            ch = cv.waitKey(50)
+            if ch == 27:
+                break
+            if ch >= ord('1') and ch <= ord('7'):
+                self.cur_marker = ch - ord('0')
+                print('marker: ', self.cur_marker)
+            if ch == ord(' ') or (self.sketch.dirty and self.auto_update):
+                self.watershed()
+                self.sketch.dirty = False
+            if ch in [ord('a'), ord('A')]:
+                self.auto_update = not self.auto_update
+                print('auto_update if', ['off', 'on'][self.auto_update])
+            if ch in [ord('r'), ord('R')]:
+                self.markers[:] = 0
+                self.markers_vis[:] = self.img
+                self.sketch.show()
+        cv.destroyAllWindows()
+
+
+if __name__ == '__main__':
+    print(__doc__)
+    import sys
+    try:
+        fn = sys.argv[1]
+    except:
+        fn = 'fruits.jpg'
+    App(cv.samples.findFile(fn)).run()