Hough lines in OpenCV/Python

Question

I'm trying to find hough lines in an image using opencv in python.

My code is:

import cv2
import numpy as np

img = cv2.imread('DLMIA.png')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)


edges = cv2.Canny(gray,100,200,apertureSize = 3)
cv2.imshow('edges',edges)
cv2.waitKey(0)

minLineLength = 30
maxLineGap = 10
lines = cv2.HoughLinesP(edges,1,np.pi/180,100,minLineLength,maxLineGap)
for x1,y1,x2,y2 in lines[0]:
    cv2.line(img,(x1,y1),(x2,y2),(0,255,0),2)

cv2.imshow('hough',img)
cv2.waitKey(0)

The image I use is .

My resulted image is .

My code example is taken from here.

The resulted image is not the same as noted in the previous link. Any help please?

Answer 1

I found the solution.

The code example only shows the first hough line.

In case you want to print all the hough lines on an image you have to print all lines.

This is the corrected code:

import cv2
import numpy as np

img = cv2.imread('dave.jpg')
gray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)


edges = cv2.Canny(gray,100,200,apertureSize = 3)
cv2.imshow('edges',edges)
cv2.waitKey(0)

minLineLength = 30
maxLineGap = 10
lines = cv2.HoughLinesP(edges,1,np.pi/180,15,minLineLength=minLineLength,maxLineGap=maxLineGap)
for x in range(0, len(lines)):
    for x1,y1,x2,y2 in lines[x]:
        cv2.line(img,(x1,y1),(x2,y2),(0,255,0),2)

cv2.imshow('hough',img)
cv2.waitKey(0)

Answer 2

I had faced the same problem it is because of the loop,

for x1,y1,x2,y2 in lines[0]:

it will take only the coordinates of first line. the array returned is 3d.

you can rectify it by using the following as loop:

for line in lines:
    for x1,y1,x2,y2 in line: