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samples/python/tutorial_code/ShapeDescriptors/moments/moments_demo.py

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+from __future__ import print_function
+from __future__ import division
+import cv2 as cv
+import numpy as np
+import argparse
+import random as rng
+
+rng.seed(12345)
+
+def thresh_callback(val):
+    threshold = val
+
+    ## [Canny]
+    # Detect edges using Canny
+    canny_output = cv.Canny(src_gray, threshold, threshold * 2)
+    ## [Canny]
+
+    ## [findContours]
+    # Find contours
+    contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)
+    ## [findContours]
+
+    # Get the moments
+    mu = [None]*len(contours)
+    for i in range(len(contours)):
+        mu[i] = cv.moments(contours[i])
+
+    # Get the mass centers
+    mc = [None]*len(contours)
+    for i in range(len(contours)):
+        # add 1e-5 to avoid division by zero
+        mc[i] = (mu[i]['m10'] / (mu[i]['m00'] + 1e-5), mu[i]['m01'] / (mu[i]['m00'] + 1e-5))
+
+    # Draw contours
+    ## [zeroMat]
+    drawing = np.zeros((canny_output.shape[0], canny_output.shape[1], 3), dtype=np.uint8)
+    ## [zeroMat]
+    ## [forContour]
+    for i in range(len(contours)):
+        color = (rng.randint(0,256), rng.randint(0,256), rng.randint(0,256))
+        cv.drawContours(drawing, contours, i, color, 2)
+        cv.circle(drawing, (int(mc[i][0]), int(mc[i][1])), 4, color, -1)
+    ## [forContour]
+
+    ## [showDrawings]
+    # Show in a window
+    cv.imshow('Contours', drawing)
+    ## [showDrawings]
+
+    # Calculate the area with the moments 00 and compare with the result of the OpenCV function
+    for i in range(len(contours)):
+        print(' * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f' % (i, mu[i]['m00'], cv.contourArea(contours[i]), cv.arcLength(contours[i], True)))
+
+## [setup]
+# Load source image
+parser = argparse.ArgumentParser(description='Code for Image Moments tutorial.')
+parser.add_argument('--input', help='Path to input image.', default='stuff.jpg')
+args = parser.parse_args()
+
+src = cv.imread(cv.samples.findFile(args.input))
+if src is None:
+    print('Could not open or find the image:', args.input)
+    exit(0)
+
+# Convert image to gray and blur it
+src_gray = cv.cvtColor(src, cv.COLOR_BGR2GRAY)
+src_gray = cv.blur(src_gray, (3,3))
+## [setup]
+
+## [createWindow]
+# Create Window
+source_window = 'Source'
+cv.namedWindow(source_window)
+cv.imshow(source_window, src)
+## [createWindow]
+## [trackbar]
+max_thresh = 255
+thresh = 100 # initial threshold
+cv.createTrackbar('Canny Thresh:', source_window, thresh, max_thresh, thresh_callback)
+thresh_callback(thresh)
+## [trackbar]
+
+cv.waitKey()