Python 3.6.4 : Testing OpenCV default Hough Line Transform.

This tutorial is about Hough Line Transform and OpenCV python module.
This can be a good example for Hough Line Transform.
See the source code:

import cv2
import numpy as np
img = cv2.imread('test_lines.jpg')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)

# filter black and gray pixels
thresh = cv2.threshold(gray, 100, 255, cv2.THRESH_BINARY_INV)[1]

# find lines
lines = cv2.HoughLinesP(thresh, 1, np.pi/180,360,18)

# output lines onto image
for line in lines:
    x1,y1,x2,y2 = line[0]
    cv2.line(img,(x1,y1),(x2,y2),(255,255,0),2)

# show image
cv2.imshow('threshold houghlines', img)
cv2.waitKey(0)
cv2.destroyAllWindows()

This is the result for test_lines.jpg .

You can test by make changes into this line of code:

lines = cv2.HoughLinesP(thresh, 1, np.pi/180,360,18)

According to documentation, the changes are influenced by the range parameters.