d6/de7/samples_2python_2snippets_2contours_8py-example.html

#!/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()

cv::imshow
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.

cv::waitKey
int waitKey(int delay=0)
Waits for a pressed key.

cv::destroyAllWindows
void destroyAllWindows()
Destroys all of the HighGUI windows.

cv::createTrackbar
int createTrackbar(const String &trackbarname, const String &winname, int *value, int count, TrackbarCallback onChange=0, void *userdata=0)
Creates a trackbar and attaches it to the specified window.

cv::ellipse
void ellipse(InputOutputArray img, Point center, Size axes, double angle, double startAngle, double endAngle, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a simple or thick elliptic arc or fills an ellipse sector.

cv::line
void line(InputOutputArray img, Point pt1, Point pt2, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws a line segment connecting two points.

cv::drawContours
void drawContours(InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar &color, int thickness=1, int lineType=LINE_8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point())
Draws contours outlines or filled contours.

cv::approxPolyDP
void approxPolyDP(InputArray curve, OutputArray approxCurve, double epsilon, bool closed)
Approximates a polygonal curve(s) with the specified precision.

cv::findContours
void findContours(InputArray image, OutputArrayOfArrays contours, OutputArray hierarchy, int mode, int method, Point offset=Point())
Finds contours in a binary image.

main
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3