# Road Lane line detection – Computer Vision Project in Python

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Lane Line detection is a critical component for self driving cars and also for computer vision in general. This concept is used to describe the path for self-driving cars and to avoid the risk of getting in another lane.

In this article, we will build a machine learning project to detect lane lines in real-time. We will do this using the concepts of computer vision using OpenCV library. To detect the lane we have to detect the white markings on both sides on the lane.

## Road Lane-Line Detection with Python & OpenCV

Using computer vision techniques in Python, we will identify road lane lines in which autonomous cars must run. This will be a critical part of autonomous cars, as the self-driving cars should not cross it’s lane and should not go in opposite lane to avoid accidents.

### Frame Masking and Hough Line Transformation

To detect white markings in the lane, first, we need to mask the rest part of the frame.Â We do this using frame masking. The frame is nothing but a NumPy array of image pixel values. To mask the unnecessary pixel of the frame, we simply update those pixel values to 0 in the NumPy array.

After making we need to detect lane lines. The technique used to detect mathematical shapes like this is called Hough Transform. Hough transformation can detect shapes like rectangles, circles, triangles, and lines.

Follow the below steps for lane line detection in Python:

1. Imports:

```import matplotlib.pyplot as plt

import numpy as np
import cv2
import os
import matplotlib.image as mpimg
from moviepy.editor import VideoFileClip
import math
```

2. Apply frame masking and find region of interest:

```def interested_region(img, vertices):
if len(img.shape) > 2:
else:

return cv2.bitwise_and(img, np.zeros_like(img))
```

3. Conversion of pixels to a line in Hough Transform space:

```def hough_lines(img, rho, theta, threshold, min_line_len, max_line_gap):
lines = cv2.HoughLinesP(img, rho, theta, threshold, np.array([]), minLineLength=min_line_len, maxLineGap=max_line_gap)
line_img = np.zeros((img.shape[0], img.shape[1], 3), dtype=np.uint8)
lines_drawn(line_img,lines)
return line_img
```

4. Create two lines in each frame after Hough transform:

```def lines_drawn(img, lines, color=[255, 0, 0], thickness=6):
global cache
global first_frame
slope_l, slope_r = [],[]
lane_l,lane_r = [],[]

Î± =0.2
for line in lines:
for x1,y1,x2,y2 in line:
slope = (y2-y1)/(x2-x1)
if slope > 0.4:
slope_r.append(slope)
lane_r.append(line)
elif slope < -0.4:
slope_l.append(slope)
lane_l.append(line)
img.shape[0] = min(y1,y2,img.shape[0])
if((len(lane_l) == 0) or (len(lane_r) == 0)):
print ('no lane detected')
return 1
slope_mean_l = np.mean(slope_l,axis =0)
slope_mean_r = np.mean(slope_r,axis =0)
mean_l = np.mean(np.array(lane_l),axis=0)
mean_r = np.mean(np.array(lane_r),axis=0)

if ((slope_mean_r == 0) or (slope_mean_l == 0 )):
print('dividing by zero')
return 1

x1_l = int((img.shape[0] - mean_l[0][1] - (slope_mean_l * mean_l[0][0]))/slope_mean_l)
x2_l = int((img.shape[0] - mean_l[0][1] - (slope_mean_l * mean_l[0][0]))/slope_mean_l)
x1_r = int((img.shape[0] - mean_r[0][1] - (slope_mean_r * mean_r[0][0]))/slope_mean_r)
x2_r = int((img.shape[0] - mean_r[0][1] - (slope_mean_r * mean_r[0][0]))/slope_mean_r)

if x1_l > x1_r:
x1_l = int((x1_l+x1_r)/2)
x1_r = x1_l
y1_l = int((slope_mean_l * x1_l ) + mean_l[0][1] - (slope_mean_l * mean_l[0][0]))
y1_r = int((slope_mean_r * x1_r ) + mean_r[0][1] - (slope_mean_r * mean_r[0][0]))
y2_l = int((slope_mean_l * x2_l ) + mean_l[0][1] - (slope_mean_l * mean_l[0][0]))
y2_r = int((slope_mean_r * x2_r ) + mean_r[0][1] - (slope_mean_r * mean_r[0][0]))
else:
y1_l = img.shape[0]
y2_l = img.shape[0]
y1_r = img.shape[0]
y2_r = img.shape[0]

present_frame = np.array([x1_l,y1_l,x2_l,y2_l,x1_r,y1_r,x2_r,y2_r],dtype ="float32")

if first_frame == 1:
next_frame = present_frame
first_frame = 0
else :
prev_frame = cache
next_frame = (1-Î±)*prev_frame+Î±*present_frame

cv2.line(img, (int(next_frame[0]), int(next_frame[1])), (int(next_frame[2]),int(next_frame[3])), color, thickness)
cv2.line(img, (int(next_frame[4]), int(next_frame[5])), (int(next_frame[6]),int(next_frame[7])), color, thickness)

cache = next_frame
```

5. Process each frame of video to detect lane:

```def weighted_img(img, initial_img, Î±=0.8, Î²=1., Î»=0.):
return cv2.addWeighted(initial_img, Î±, img, Î², Î»)

def process_image(image):

global first_frame

gray_image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
img_hsv = cv2.cvtColor(image, cv2.COLOR_RGB2HSV)

lower_yellow = np.array([20, 100, 100], dtype = "uint8")
upper_yellow = np.array([30, 255, 255], dtype="uint8")

canny_edges=cv2.Canny(gauss_gray, 50, 150)

imshape = image.shape
lower_left = [imshape[1]/9,imshape[0]]
lower_right = [imshape[1]-imshape[1]/9,imshape[0]]
top_left = [imshape[1]/2-imshape[1]/8,imshape[0]/2+imshape[0]/10]
top_right = [imshape[1]/2+imshape[1]/8,imshape[0]/2+imshape[0]/10]
vertices = [np.array([lower_left,top_left,top_right,lower_right],dtype=np.int32)]
roi_image = interested_region(canny_edges, vertices)

theta = np.pi/180

line_image = hough_lines(roi_image, 4, theta, 30, 100, 180)
result = weighted_img(line_image, image, Î±=0.8, Î²=1., Î»=0.)
return result
```

6. Clip the input video to frames and get the resultant output video file:

```first_frame = 1
white_output = '__path_to_output_file__'
clip1 = VideoFileClip("__path_to_input_file__")
white_clip = clip1.fl_image(process_image)
white_clip.write_videofile(white_output, audio=False)
```

### Code for Lane Line Detection Project GUI:

```import tkinter as tk
from tkinter import *
import cv2
from PIL import Image, ImageTk
import os
import numpy as np

global last_frame1
last_frame1 = np.zeros((480, 640, 3), dtype=np.uint8)
global last_frame2
last_frame2 = np.zeros((480, 640, 3), dtype=np.uint8)
global cap1
global cap2
cap1 = cv2.VideoCapture("path_to_input_test_video")
cap2 = cv2.VideoCapture("path_to_resultant_lane_detected_video")

def show_vid():
if not cap1.isOpened():
print("cant open the camera1")
frame1 = cv2.resize(frame1,(400,500))
if flag1 is None:
print ("Major error!")
elif flag1:
global last_frame1
last_frame1 = frame1.copy()
pic = cv2.cvtColor(last_frame1, cv2.COLOR_BGR2RGB)
img = Image.fromarray(pic)
imgtk = ImageTk.PhotoImage(image=img)
lmain.imgtk = imgtk
lmain.configure(image=imgtk)
lmain.after(10, show_vid)

def show_vid2():
if not cap2.isOpened():
print("cant open the camera2")
frame2 = cv2.resize(frame2,(400,500))
if flag2 is None:
print ("Major error2!")
elif flag2:
global last_frame2
last_frame2 = frame2.copy()
pic2 = cv2.cvtColor(last_frame2, cv2.COLOR_BGR2RGB)
img2 = Image.fromarray(pic2)
img2tk = ImageTk.PhotoImage(image=img2)
lmain2.img2tk = img2tk
lmain2.configure(image=img2tk)
lmain2.after(10, show_vid2)

if __name__ == '__main__':
root=tk.Tk()
lmain = tk.Label(master=root)
lmain2 = tk.Label(master=root)

lmain.pack(side = LEFT)
lmain2.pack(side = RIGHT)
root.title("Lane-line detection")
root.geometry("900x700+100+10")
exitbutton = Button(root, text='Quit',fg="red",command=   root.destroy).pack(side = BOTTOM,)
show_vid()
show_vid2()
root.mainloop()
cap.release()
```

## Summary

This is an intermediate Python project in machine learning, which is helpful for the data science aspirants to master machine learning and gain expertise.

In this lane line detection project, we use OpenCV. Before detecting lane lines, we masked remaining objects and then identified the line with Hough transformation.

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### 31 Responses

1. lusifer says:

gray_image = cv2.cvtColor(image, cv2.COLOmean_r[0][1] – (slope_mean_r * mean_r[0][0])BGR2GRAY)
^
SyntaxError: invalid syntax.

• e says:

same

• sameer says:

gray_image = cv2.cvtColor(image, cv2.COLOmean_r[0][1] â€“ (slope_mean_r * mean_r[0][0])BGR2GRAY),

2. Jeremy Evert says:

CentOS 7.8, Python 3. We had the same error as lusifer

3. MANAV KALRA says:

Could anyone solve the problem?

4. Aashique Roshan says:

gray_image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)

5. Ike says:

there is an error in step 4
for line in lines:
for x1,y1,x2,y2 in line:
slope = (y2-y1)/(x2-x1)

for line in lines: returns none hence not iterateable. anyone with a solution

• key says:

position line 7 is incorrect. u can tab that line

• venkat kommineni says:

yrs

Same problem as Ike. Can someone please share the solution?

Thanks!

7. bonny-4 says:

Same error here as Ike.
for line in lines:
TypeError: ‘NoneType’ object is not iterable

Someone found a solution ?
THX

8. SURAJ AGARWAL says:

CAN U SHARE ME YOUR DOCUMENTATION

• Varshita Rajana says:

9. Ashok kumar says:

How to run it on my PC

10. Amogh says:

did u found the solution

11. Varshita Rajana says:

Did anyone draw uml diagrams for this project??. Please send me..!

• Vempati Ravi Teja says:

hi have u done projet report on this?

12. Vempati Ravi Teja says:

hi do u have documentation

13. Harish says:

I want this project UML diagrams

• Srijani says:

Have you got the uml diagrams.
If then please send me sir..

14. Anna Harish says:

I want this…lane line detection project UML diagrams… please send me sir.

15. govind says:

lane line detection project UML diagramsâ€¦

• Srijani says:

Have you got the uml diagrams.
If then please send me sir..

16. Janani says:

can anyone help me out for this project to complete

• Bhushan says:

Hi , I am also doing this project. I am also going through some errors, Can you tell me which error you are getting?

17. Bhushan says:

Hi , I am also doing this project. I am also going through some errors, Can you tell me which error you are getting?

18. Bhushan says:

Do you implemented it ?

19. Sana ullah khan says:

I’m inspired to do this as my final year project, but I don’t know the requirements that I would need for this project. please shortlist for me all the requirements.

Thank you!

• Anonymous says:

Install the requirements first , all are mentioned there already .

20. key says:

i try this algoritma but i have error in moviepy.editor maybe someone can help me how to instal that

Correct code –

main.py –

import matplotlib.pyplot as plt

import numpy as np
import cv2
import os
import matplotlib.image as mpimg
from moviepy.editor import VideoFileClip
import math

def interested_region(img, vertices):
if len(img.shape) > 2:
else:

def lines_drawn(img, lines, color=[255, 0, 0], thickness=6):
global cache
global first_frame
slope_l, slope_r = [],[]
lane_l,lane_r = [],[]

Î± =0.2

for line in lines:
for x1,y1,x2,y2 in line:
slope = (y2-y1)/(x2-x1)
if slope > 0.4:
slope_r.append(slope)
lane_r.append(line)
elif slope x1_r:
x1_l = int((x1_l+x1_r)/2)
x1_r = x1_l
y1_l = int((slope_mean_l * x1_l ) + mean_l[0][1] – (slope_mean_l * mean_l[0][0]))
y1_r = int((slope_mean_r * x1_r ) + mean_r[0][1] – (slope_mean_r * mean_r[0][0]))
y2_l = int((slope_mean_l * x2_l ) + mean_l[0][1] – (slope_mean_l * mean_l[0][0]))
y2_r = int((slope_mean_r * x2_r ) + mean_r[0][1] – (slope_mean_r * mean_r[0][0]))
else:
y1_l = img.shape[0]
y2_l = img.shape[0]
y1_r = img.shape[0]
y2_r = img.shape[0]

present_frame = np.array([x1_l,y1_l,x2_l,y2_l,x1_r,y1_r,x2_r,y2_r],dtype =”float32″)

if first_frame == 1:
next_frame = present_frame
first_frame = 0
else :
prev_frame = cache
next_frame = (1-Î±)*prev_frame+Î±*present_frame

cv2.line(img, (int(next_frame[0]), int(next_frame[1])), (int(next_frame[2]),int(next_frame[3])), color, thickness)
cv2.line(img, (int(next_frame[4]), int(next_frame[5])), (int(next_frame[6]),int(next_frame[7])), color, thickness)

cache = next_frame

def hough_lines(img, rho, theta, threshold, min_line_len, max_line_gap):
lines = cv2.HoughLinesP(img, rho, theta, threshold, np.array([]), minLineLength=min_line_len, maxLineGap=max_line_gap)
line_img = np.zeros((img.shape[0], img.shape[1], 3), dtype=np.uint8)
lines_drawn(line_img,lines)
return line_img

def weighted_img(img, initial_img, Î±=0.8, Î²=1., Î»=0.):
return cv2.addWeighted(initial_img, Î±, img, Î², Î»)

def process_image(image):
global first_frame

gray_image = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)

lower_yellow = np.array([20, 100, 100], dtype = “uint8″)
upper_yellow = np.array([30, 255, 255], dtype=”uint8”)

canny_edges=cv2.Canny(gauss_gray, 50, 150)

imshape = image.shape
lower_left = [imshape[1]/9,imshape[0]]
lower_right = [imshape[1]-imshape[1]/9,imshape[0]]
top_left = [imshape[1]/2-imshape[1]/8,imshape[0]/2+imshape[0]/10]
top_right = [imshape[1]/2+imshape[1]/8,imshape[0]/2+imshape[0]/10]
vertices = [np.array([lower_left,top_left,top_right,lower_right],dtype=np.int32)]
roi_image = interested_region(canny_edges, vertices)

theta = np.pi/180

line_image = hough_lines(roi_image, 4, theta, 30, 100, 180)
result = weighted_img(line_image, image, Î±=0.8, Î²=1., Î»=0.)
return result

gui.py –

import tkinter as tk
from tkinter import *
import cv2
from PIL import Image, ImageTk
import numpy as np

global last_frame1
last_frame1 = np.zeros((480, 640, 3), dtype=np.uint8)
global last_frame2
last_frame2 = np.zeros((480, 640, 3), dtype=np.uint8)
cap1 = cv2.VideoCapture(“./input2.mp4”)
cap2 = cv2.VideoCapture(“./output2.mp4”)

def show_vid():
if not cap1.isOpened():
print(“Can’t open the camera1”)
return
frame1 = cv2.resize(frame1, (600, 500))
if flag1:
global last_frame1
last_frame1 = frame1.copy()
pic = cv2.cvtColor(last_frame1, cv2.COLOR_BGR2RGB)
img = Image.fromarray(pic)
imgtk = ImageTk.PhotoImage(image=img)
lmain.imgtk = imgtk
lmain.configure(image=imgtk)
lmain.after(10, show_vid)

def show_vid2():
if not cap2.isOpened():
print(“Can’t open the camera2″)
return
frame2 = cv2.resize(frame2, (600, 500))
if flag2:
global last_frame2
last_frame2 = frame2.copy()
pic2 = cv2.cvtColor(last_frame2, cv2.COLOR_BGR2RGB)
img2 = Image.fromarray(pic2)
img2tk = ImageTk.PhotoImage(image=img2)
lmain2.img2tk = img2tk
lmain2.configure(image=img2tk)
lmain2.after(10, show_vid2)

if __name__ == ‘__main__’:
root = tk.Tk()
heading = Label(root, image=img, text=”Lane-Line Detection”)
lmain = tk.Label(master=root)
lmain2 = tk.Label(master=root)

lmain.pack(side=LEFT)
lmain2.pack(side=RIGHT)
root.title(“Lane-line detection”)
root.geometry(“1250×900+100+10″)

exitbutton = Button(root, text=’Quit’, fg=”red”, command=root.destroy)
exitbutton.pack(side=BOTTOM)
show_vid()
show_vid2()
root.mainloop()
cap1.release()
cap2.release()

Note : Change the files path location as per your configuration.

To run the files ->

1. Go to the File location
2. Open it in command prompt or anaconda prompt
3. Install the Required libraries (pip install library name)
4. To run the file (python main.py) or (python gui.py)
This should display 2 images without lane and with lane detection in parallel.

Hope this will work as per your configuration.

Happy Learning!