CODEWITHSUNDEEP
python-2.7opencv
zinon
zinon

Reputation: 4664

Hough lines in OpenCV/Python

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 this.

My resulted image is this.

My code example is taken from here.

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

Upvotes: 6

Views: 35400

Answers (3)

robe
robe

Reputation: 51

A bit more elegant solution would be to use

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

Upvotes: 5

zinon
zinon

Reputation: 4664

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)

Upvotes: 31

thomachan
thomachan

Reputation: 398

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:

Upvotes: 4

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