cv2.createTrackbar using python

Question

I'm a newbie in python and opencv, I want to create a track-bar to control the hierarchy of the function cv2.findContours but I don't know how to add it to the source code her is the code:

import cv2
import cv2.cv as cv

cv2.namedWindow("test")
vc = cv2.VideoCapture(2);
retVal, frame = vc.read();
while True:
    if frame is not None:   
        imgray = cv2.cvtColor(frame,cv2.COLOR_BGR2GRAY)
        ret,thresh = cv2.threshold(imgray,127,255,0)
        contours, hierarchy = cv2.findContours(thresh,cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

        cv2.drawContours(frame, contours, -1, (0,255,0), 2)

        cv2.imshow("test", frame)

     rval, frame = vc.read()

     if cv2.waitKey(1) & 0xFF == 27:
          break

cv.DestroyAllWindows()

thank you in advance

Answer 1

I hope you have solved your problems by now, but I will try to explain it in case you haven't. You can create a window using the named window function and then associate the trackbar to that window.

cv2.namedWindow('test')
cv2.createTrackbar('thrs1', 'test', 300, 800, callback)
# Do whatever you want with contours
cv2.imshow('test', frame)

You will find the function createTrackbar explained here: cv2.createTrackbar

callback is pointer to the function that will be called everytime the slides changes it's position.