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hackassin
GitHub Repository: hackassin/learnopencv
 Path: blob/master/Contour-Detection-using-OpenCV/python/contour_approximations/contour_approx.py
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import cv2

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# read the image

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image = cv2.imread('../../input/image_1.jpg')

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# convert the image to grayscale format

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img_gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

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# apply binary thresholding

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ret, thresh = cv2.threshold(img_gray, 150, 255, cv2.THRESH_BINARY)

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# visualize the binary image

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cv2.imshow('Binary image', thresh)

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cv2.waitKey(0)

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cv2.imwrite('image_thres1.jpg', thresh)

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cv2.destroyAllWindows()

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# detect the contours on the binary image using cv2.CHAIN_APPROX_NONE

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contours, hierarchy = cv2.findContours(image=thresh, mode=cv2.RETR_TREE, 

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                                       method=cv2.CHAIN_APPROX_NONE)

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# draw contours on the original image

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image_copy = image.copy()

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cv2.drawContours(image=image_copy, contours=contours, contourIdx=-1, 

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                 color=(0, 255, 0), thickness=2, lineType=cv2.LINE_AA)

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# see the results

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cv2.imshow('None approximation', image_copy)

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cv2.waitKey(0)

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cv2.imwrite('contours_none_image1.jpg', image_copy)

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cv2.destroyAllWindows()

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"""

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Now let's try with `cv2.CHAIN_APPROX_SIMPLE`

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"""

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# detect the contours on the binary image using cv2.ChAIN_APPROX_SIMPLE

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contours1, hierarchy1 = cv2.findContours(thresh, cv2.RETR_TREE, 

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                                                cv2.CHAIN_APPROX_SIMPLE)

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# draw contours on the original image for `CHAIN_APPROX_SIMPLE`

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image_copy1 = image.copy()

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cv2.drawContours(image_copy1, contours1, -1, (0, 255, 0), 2, 

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                 cv2.LINE_AA)

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# see the results

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cv2.imshow('Simple approximation', image_copy1)

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cv2.waitKey(0)

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cv2.imwrite('contours_simple_image1.jpg', image_copy1)

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cv2.destroyAllWindows()

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# to actually visualize the effect of `CHAIN_APPROX_SIMPLE`, we need a proper image

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image1 = cv2.imread('../../input/image_2.jpg')

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img_gray1 = cv2.cvtColor(image1, cv2.COLOR_BGR2GRAY)

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ret, thresh1 = cv2.threshold(img_gray1, 150, 255, cv2.THRESH_BINARY)

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contours2, hierarchy2 = cv2.findContours(thresh1, cv2.RETR_TREE, 

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                                                cv2.CHAIN_APPROX_SIMPLE)

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image_copy2 = image1.copy()

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cv2.drawContours(image_copy2, contours2, -1, (0, 255, 0), 2, 

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                 cv2.LINE_AA)

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cv2.imshow('SIMPLE Approximation contours', image_copy2)

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cv2.waitKey(0)

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image_copy3 = image1.copy()

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for i, contour in enumerate(contours2): # loop over one contour area

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    for j, contour_point in enumerate(contour): # loop over the points 

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        # draw a circle on the current contour coordinate

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        cv2.circle(image_copy3, ((contour_point[0][0], contour_point[0][1])), 

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                   2, (0, 255, 0), 2, cv2.LINE_AA)

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# see the results

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cv2.imshow('CHAIN_APPROX_SIMPLE Point only', image_copy3)

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cv2.waitKey(0)

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cv2.imwrite('contour_point_simple.jpg', image_copy3)

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cv2.destroyAllWindows()

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